Orbital projection technique to explore the materials genomes of optical susceptibilities & nbsp;& nbsp;
}, volume={12}, ISSN={["2158-3226"]}, DOI={10.1063/5.0067891}, abstractNote={The development in materials science and pharmaceutics shows that there exist some key materials genomes, i.e., certain groups of atoms with specific constituents and structures, which govern the property of a series of materials based on them. To pinpoint such materials, genomes are helpful to assemble functional units and synthesize new materials and, thus, have a profound meaning. In this work, we develop an innovative method based on the idea of projecting atomic orbitals’ wavefunction, which enables us to project every physical quantity into their orbital contribution and, thus, can be widely used to identify the materials genomes of various properties. Within this framework, we derive the expressions of the projected optical susceptibilities and exhibit a paradigm of studying the corresponding materials genomes of optical properties, especially the desired nonlinear optical materials.}, number={5}, journal={AIP ADVANCES}, author={Li, ZhenHua and Deng, Shuiquan and Whangbo, Myung-Hwan and Luo, Hong-Gang}, year={2022}, month={May} } @article{whangbo_koo_bruecher_puphal_kremer_2022, title={Absence of Spin Frustration in the Kagome Layers of Cu2+ Ions in Volborthite Cu3V2O7(OH)(2)center dot 2H(2)O and Observation of the Suppression and Re-Entrance of Specific Heat Anomalies in Volborthite under an External Magnetic Field}, volume={7}, ISSN={["2410-3896"]}, DOI={10.3390/condmat7010024}, abstractNote={We determined the spin exchanges between the Cu2+ ions in the kagome layers of volborthite, Cu3V2O7(OH)2x2H2O, by performing the energy-mapping analysis based on DFT+U calculations, to find that the kagom\'e layers of Cu2+ ions are hardly spin-frustrated, and the magnetic properties of volborthite below ~75 K should be described by very weakly interacting antiferromagnetic uniform chains made up of effective S=1/2 pseudospin units. This conclusion was verified by synthesizing single crystals of not only Cu3V2O7(OH)2x2H2O but also its deuterated analogue Cu3V2O7(OD)2x2D2O and then by investigating their magnetic susceptibilities and specific heats. Each kagome layer consists of intertwined two-leg spin ladders with rungs of linear spin trimers. With the latter acting as S=1/2 pseudospin units, each two-leg spin ladder behaves as a chain of S=1/2 pseudospins. Adjacent two-leg spin ladders in each kagome layer interact very weakly, so it is required that all nearest-neighbor spin exchange paths of every two-leg spin ladder remain antiferromagnetically coupled in all spin ladder arrangements of a kagome layer. This constraint imposes three sets of entropy spectra with which each kagome layer can exchange energy with the surrounding on lowering the temperature below ~1.5 K and on raising the external magnetic field B. We discovered that the specific heat anomalies of volborthite observed below ~1.5 K at B = 0 are suppressed by raising the magnetic field B to ~4.2 T, that a new specific heat anomaly occurs when B is increased above ~5.5 T, and that the imposed three sets of entropy spectra are responsible for the field-dependence of the specific heat anomalies.}, number={1}, journal={CONDENSED MATTER}, author={Whangbo, Myung-Hwan and Koo, Hyun-Joo and Bruecher, Eva and Puphal, Pascal and Kremer, Reinhard K.}, year={2022}, month={Mar} } @article{koo_kremer_whangbo_2022, title={High-Spin Orbital Interactions Across van der Waals Gaps Controlling the Interlayer Ferromagnetism in van der Waals Ferromagnets}, ISSN={["1520-5126"]}, DOI={10.1021/jacs.2c06741}, abstractNote={We examined what interactions control the sign and strength of the interlayer coupling in van der Waals ferromagnets such as Fe3-xGeTe2, Cr2Ge2Te6, CrI3, and VI3 to find that high-spin orbital interactions across the van der Waals gaps are a key to understanding their ferromagnetism. Interlayer ferromagnetic coupling in Fe3-xGeTe2, Cr2Ge2Te6, and CrI3 is governed by the high-spin two-orbital two-electron destabilization, but that in VI3 by the high-spin four-orbital two-electron stabilization. These interactions explain a number of seemingly puzzling observations in van der Waals ferromagnets.}, journal={JOURNAL OF THE AMERICAN CHEMICAL SOCIETY}, author={Koo, Hyun-Joo and Kremer, Reinhard K. and Whangbo, Myung-Hwan}, year={2022}, month={Aug} } @article{moskin_kozlyakova_shvanskaya_chareev_koo_whangbo_vasiliev_2022, title={Highly anisotropic 1/3-magnetization plateau in a ferrimagnet Cs2Cu3(SeO3)(4)center dot 2H(2)O: topology of magnetic bonding necessary for magnetization plateau}, volume={52}, ISSN={["1477-9234"]}, DOI={10.1039/d2dt03517k}, abstractNote={We prepared Cs2Cu3(SeO3)4·2H2O composed of Cu2+ ions at square-planar coordination sites and characterized its structural and magnetic properties, to show that Cs2Cu3(SeO3)4·2H2O is a ferrimagnet exhibiting a highly anisotropic 1/3-magnetization plateau. This unprecedented anisotropy in a magnetization plateau is the consequence of three effects, namely, the orthogonal arrangements of the corner-sharing CuO4 square planes, the nearest-neighbour antiferromagnetic exchange, and the anisotropic g-factor of the Cu2+ ions at square-planar coordination sites. By analyzing the topology of magnetic bonding, we found why magnetic plateaus are observed only for certain ferrimagnets and antiferromagnets.}, number={1}, journal={DALTON TRANSACTIONS}, author={Moskin, A. V. and Kozlyakova, E. S. and Shvanskaya, L. V. and Chareev, D. A. and Koo, Hyun-Joo and Whangbo, Myung-Hwan and Vasiliev, A. N.}, year={2022}, month={Dec}, pages={118–127} } @article{vasilchikova_vasiliev_evstigneeva_nalbandyan_lee_koo_whangbo_2022, title={Magnetic Properties of A(2)Ni(2)TeO(6) (A = K, Li): Zigzag Order in the Honeycomb Layers of Ni2+ Ions Induced by First and Third Nearest-Neighbor Spin Exchanges}, volume={15}, ISSN={["1996-1944"]}, DOI={10.3390/ma15072563}, abstractNote={The static and dynamic magnetic properties and the specific heat of K2Ni2TeO6 and Li2Ni2TeO6 were examined and it was found that they undergo a long-range ordering at TN = 22.8 and 24.4 K, respectively, but exhibit a strong short-range order. At high temperature, the magnetic susceptibilities of K2Ni2TeO6 and Li2Ni2TeO6 are described by a Curie-Weiss law, with Curie-Weiss temperatures Θ of approximately -13 and -20 K, respectively, leading to the effective magnetic moment of about 4.46 ± 0.01 μB per formula unit, as expected for Ni2+ (S = 1) ions. In the paramagnetic region, the ESR spectra of K2Ni2TeO6 and Li2Ni2TeO6 show a single Lorentzian-shaped line characterized by the isotropic effective g-factor, g = 2.19 ± 0.01. The energy-mapping analysis shows that the honeycomb layers of A2Ni2TeO6 (A = K, Li) and Li3Ni2SbO6 adopt a zigzag order, in which zigzag ferromagnetic chains are antiferromagnetically coupled, because the third nearest-neighbor spin exchanges are strongly antiferromagnetic while the first nearest-neighbor spin exchanges are strongly ferromagnetic, and that adjacent zigzag-ordered honeycomb layers prefer to be ferromagnetically coupled. The short-range order of the zigzag-ordered honeycomb lattices of K2Ni2TeO6 and Li2Ni2TeO6 is equivalent to that of an antiferromagnetic uniform chain, and is related to the short-range order of the ferromagnetic chains along the direction perpendicular to the chains.}, number={7}, journal={MATERIALS}, author={Vasilchikova, Tatyana and Vasiliev, Alexander and Evstigneeva, Maria and Nalbandyan, Vladimir and Lee, Ji-Sun and Koo, Hyun-Joo and Whangbo, Myung-Hwan}, year={2022}, month={Apr} } @misc{jiang_deng_whangbo_guo_2022, title={Material research from the viewpoint of functional motifs}, volume={9}, ISSN={["2053-714X"]}, DOI={10.1093/nsr/nwac017}, abstractNote={As early as 2001, the need for the 'functional motif theory' was pointed out, to assist the rational design of functional materials. The properties of materials are determined by their functional motifs and how they are arranged in the materials. Uncovering functional motifs and their arrangements is crucial in understanding the properties of materials and rationally designing new materials of desired properties. The functional motifs of materials are the critical microstructural units (e.g. constituent components and building blocks) that play a decisive role in generating certain material functions, and can not be replaced with other structural units without the loss, or significant suppression, of relevant functions. The role of functional motifs and their arrangement in materials, with representative examples, is presented. The microscopic structures of these examples can be classified into six types on a length scale smaller than ∼10 nm with maximum subatomic resolution, i.e. crystal, magnetic, aperiodic, defect, local and electronic structures. Functional motif analysis can be employed in the function-oriented design of materials, as elucidated by taking infrared non-linear optical materials as an example. Machine learning is more efficient in predicting material properties and screening materials with high efficiency than high-throughput experimentation and high-throughput calculations. In order to extract functional motifs and find their quantitative relationships, the development of sufficiently reliable databases for material structures and properties is imperative.}, number={7}, journal={NATIONAL SCIENCE REVIEW}, author={Jiang, Xiao-Ming and Deng, Shuiquan and Whangbo, Myung-Hwan and Guo, Guo-Cong}, year={2022}, month={Aug} } @article{xu_huang_cheng_whangbo_deng_2022, title={Microscopic Mechanism of the Heat-Induced Blueshift in Phosphors and a Logarithmic Energy Dependence on the Nearest Dopant-Vacancy Distance}, ISSN={["1521-3773"]}, DOI={10.1002/anie.202116404}, abstractNote={Heat-induced blueshift (HIB) observed in many luminescent materials is a puzzling phenomenon that has remained unexplained for decades. By using the high-throughput first-principles calculations and energy-screening techniques, we generated a number of model structures for five phosphors, RbLi[Li3 SiO4 ]2 :Eu2+ , Na[Li3 SiO4 ]:Eu2+ , K[Li3 SiO4 ]:Eu2+ , Sr[LiAl3 N4 ]:Eu2+ , and Ca[LiAl3 N4 ]:Eu2+ . Our analyses suggest, to a first approximation, a logarithmic energy dependence on the nearest distance between the dopant and the metal-cation vacancy. By identifying the 5d→4f transition energies from the electronic structures calculated for the screened model structures, we show that the vibration of the Eu2+ ion lying in an asymmetric and anharmonic potential well couples with the electronic states, leading to their HIB phenomena.}, journal={ANGEWANDTE CHEMIE-INTERNATIONAL EDITION}, author={Xu, Jing and Huang, Xueli and Cheng, Xiyue and Whangbo, Myung-Hwan and Deng, Shuiquan}, year={2022}, month={Feb} } @article{kremer_bette_bruecher_nuss_schulz_whangbo_koo_2022, title={Multiple strongly coupled antiferromagnetic spin S=1/2 dimers in liroconite Cu2Al(As,P)O-4(OH)(4)center dot 4H(2)O}, ISSN={["2196-7105"]}, DOI={10.1515/zkri-2022-0040}, abstractNote={Abstract We report on the magneto-structural properties of the rare copper aluminum hydroxo-arsenate mineral liroconite with chemical composition Cu 2 AlAs 1− x P x O 4 (OH) 4 ·4H 2 O ( x ≈ 0.2). In order to characterize the natural mineral sample chemical analyses, X-ray single crystal and powder diffraction, heat capacity and crystal water desorption, anisotropic thermal expansion and Raman scattering and magnetic susceptibility investigations have been carried out. The magnetic properties are well described by two discrete oxygen bridged Cu 2+ spin S = 1/2 dimers with antiferromagnetic spin exchange ranging between −320 K and −136 K, depending on to which group-15 five-valent cation, As 5+ or P 5+ , the dimer bridging oxygen atoms coordinate to. Accordingly the temperature dependence of the magnetic susceptibilities can be well fitted to a sum of two Bleaney–Bowers type spin S = 1/2 dimer susceptibilities suggesting that the dimers show negligible mixed coordination to (AsO 4 ) 3− /(PO 4 ) 3− tetrahedra. DFT + U calculation confirm the ratio of the spin exchange parameters of the (AsO 4 ) 3− or (PO 4 ) 3− coordinated Cu 2+ – Cu 2+ dimers. Inter dimer spin exchange is about two orders of magnitude smaller than intra dimer exchange.}, journal={ZEITSCHRIFT FUR KRISTALLOGRAPHIE-CRYSTALLINE MATERIALS}, author={Kremer, Reinhard K. and Bette, Sebastian and Bruecher, Eva and Nuss, Juergen and Schulz, Armin and Whangbo, Myung-Hwan and Koo, Hyun-Joo}, year={2022}, month={Sep} } @article{almoussawi_yao_guo_whangbo_dupray_clevers_deng_kabbour_2022, title={Negative Second Harmonic Response of Sn(4+)in the Fresnoite Oxysulfide Ba2SnSSi2O7}, volume={34}, ISSN={["1520-5002"]}, DOI={10.1021/acs.chemmater.1c04296}, abstractNote={Oxychalcogenides are promising candidates for the design of IR nonlinear optical materials. Here, we prepared the first oxysulfide in the polar Fresnoite mineral type, Ba2SnSSi2O7, and show that it has rare tin square pyramids, SnO4S, with apical Sn–S bond. These units and the Si2O7 groups are corner-shared to form the SnSSi2O7 layer with their Sn–S and apical Si–O bonds pointed along the polar c axis. Second harmonic generation measurements reveal that Ba2SnSSi2O7 is an IR nonlinear optical (NLO) compound. Formally, Ba2SnSSi2O7 results from the mineral Fresnoite, Ba2TiOSi2O7, by replacing the TiO5 square pyramid with the SnO4S square pyramid. This substitution increases the apical/the equatorial bond ratio of the square pyramid, namely, Ti–Oap/Ti–Oeq = 1.66/2.00 = 0.83 in TiO5, and Sn–S/Sn–O = 2.03/2.31 = 0.88 in SnO4S. This change has a major impact on the cleavage along the stacking polar c axis and on the second harmonic generation response, which decreases from Ba2TiOSi2O7 to Ba2SnSSi2O7 by a factor greater than 2. The atom response theory analyses based on the density functional theory calculations reveal a remarkable difference between Ba2TiOSi2O7 and Ba2SnSSi2O7; the second harmonic generation is positive for the Ti4+ ion of Ba2TiOSi2O7 but negative for the Sn4+ ion of Ba2SnSSi2O7. A Tauc plot analysis for Ba2SnSSi2O7 assuming indirect and direct transitions led to the optical band gaps of 2.4 and 2.7 eV, respectively.}, number={10}, journal={CHEMISTRY OF MATERIALS}, author={Almoussawi, Batoul and Yao, Wen-Dong and Guo, Sheng-Ping and Whangbo, Myung-Hwan and Dupray, Valerie and Clevers, Simon and Deng, Shuiquan and Kabbour, Houria}, year={2022}, month={May}, pages={4375–4383} } @article{vasiliev_berdonosov_kozlyakova_maximova_murtazoev_dolgikh_lyssenko_pchelkina_gorbunov_chung_et al._2022, title={Observation of a 1/3 magnetization plateau in Pb2Cu10O4(SeO3)(4)Cl-7 arising from (Cu2+)(7) clusters of corner-sharing (Cu2+)(4) tetrahedra}, ISSN={["1477-9234"]}, DOI={10.1039/d2dt02316d}, abstractNote={A mixed-valence compound Pb2Cu10O4(SeO3)4Cl7 has a complex structure consisting of one nonmagnetic Cu+ (S = 0) ion and four nonequivalent magnetic Cu2+ (S = 1/2) ions. It exhibits antiferromagnetic ordering at TN = 10.2 K. At a temperature below TN, a sequence of spin-flop transition at Bspin-flop = 1.3 T and 1/3 plateau formation at Bspin-flip = 4.4 K is observed in the magnetization curve M(B). The 1/3 magnetization plateau persists at least up to 53.5 T. The spin exchanges of Pb2Cu10O4(SeO3)4Cl7 evaluated by performing energy-mapping analysis based on DFT+U calculations show that the magnetic properties of Pb2Cu10O4(SeO3)4Cl7 are described by the (Cu2+)7 cluster of corner-sharing (Cu2+)4 tetrahedra, and that each (Cu2+)7 cluster has a S = 3/2 spin arrangement in the ground state. The 1/3 magnetization plateau observed for Pb2Cu10O4(SeO3)4Cl7 is explained by the field-induced flip of every second (Cu2+)7 cluster within a unit cell.}, journal={DALTON TRANSACTIONS}, author={Vasiliev, A. N. and Berdonosov, P. S. and Kozlyakova, E. S. and Maximova, O. and Murtazoev, A. F. and Dolgikh, V. A. and Lyssenko, K. A. and Pchelkina, Z. and Gorbunov, D. and Chung, S. H. and et al.}, year={2022}, month={Sep} } @article{amano patino_denis romero_koo_avdeev_injac_goto_whangbo_shimakawa_2022, title={Orthogonal antiferromagnetism to canted ferromagnetism in CaCo3Ti4O12 quadruple perovskite driven by underlying kagome lattices}, volume={3}, ISSN={["2662-4443"]}, DOI={10.1038/s43246-022-00274-y}, abstractNote={Abstract AA ′ 3 B 4 O 12 quadruple perovskites, with magnetic A ′ and non-magnetic B cations, are characterized by a wide range of complex magnetic structures. These are due to a variety of competing spin-exchange interactions up to the fourth nearest neighbours. Here, we synthesize and characterize the magnetic behaviour of the CaCo 3 Ti 4 O 12 quadruple perovskite. We find that in the absence of an external magnetic field, the system undergoes antiferromagnetic ordering at 9.3 K. This magnetic structure consists of three interpenetrating mutually orthogonal magnetic sublattices. Under an applied magnetic field, this antiferromagnetic structure evolves into a canted ferromagnetic structure. In explaining these magnetic structures, as well as the seemingly unrelated magnetic structures found in other quadruple perovskites, we suggest a crucial role played by the underlying kagome lattices in these systems. All observed magnetic structures of these materials represent indeed one of the three possible ways to reduce spin frustration in the A ′ site kagome layers. More specifically, our survey of the magnetic structures observed for quadruple perovskites AA ′ 3 B 4 O 12 reveals the following three ways to reduce spin frustration, namely to make each layer ferromagnetic, to adopt a compromise 120° spin arrangement in each layer, or to have a magnetic structure with a vanishing sum of all second nearest-neighbour spin exchanges.}, number={1}, journal={COMMUNICATIONS MATERIALS}, author={Amano Patino, Midori and Denis Romero, Fabio and Koo, Hyun-Joo and Avdeev, Maxim and Injac, Sean D. A. and Goto, Masato and Whangbo, Myung-Hwan and Shimakawa, Yuichi}, year={2022}, month={Aug} } @article{yang_huang_cheng_maggard_whangbo_luan_deng_2022, title={Prediction of Large Second Harmonic Generation in the Metal-Oxide/Organic Hybrid Compound CuMoO3(p2c)}, volume={14}, ISSN={["2073-8994"]}, url={https://www.mdpi.com/2073-8994/14/4/824}, DOI={10.3390/sym14040824}, abstractNote={Noncentrosymmetric hybrid framework (HF) materials are an important system in discovering new practical second-order nonlinear optical materials. We calculated the second harmonic generation (SHG) response of a noncentrosymmetric (NCS) organic–inorganic HF compound, CuMoO3(p2c) (p2c = pyrazine-2-carboxylate) to find that it exhibits the largest SHG response among all known NCS HF materials with one-dimensional helical chains. Further atom response theory analysis revealed that the metal atoms Cu and Mo contribute much more strongly than do nonmetal atoms in determining the strength of the SHG response, which is a novel example in nonlinear optical materials known to date.}, number={4}, journal={SYMMETRY-BASEL}, author={Yang, Tingting and Huang, Xueli and Cheng, Xiyue and Maggard, Paul A. and Whangbo, Myung-Hwan and Luan, Chengkai and Deng, Shuiquan}, year={2022}, month={Apr} } @article{markina_vasilchikova_kuznetsova_berdonosov_olenev_chung_koo_whangbo_vasiliev_2022, title={Preparation and Characterization of Francisite Solid Solutions Cu3Bi(S(e1-x)TexO(3))(2)O2Br (x=0-1): Possibility for Francisites as Starting Materials for Oxide van der Waals Ferromagnets}, ISSN={["1520-5002"]}, DOI={10.1021/acs.chemmater.2c02865}, abstractNote={We synthesized the solid solutions Cu3Bi(Se1–xTexO3)2O2Br (x = 0, 0.25, 0.5, 0.75, 1) for the first time and characterized their structures by X-ray diffraction (XRD) measurements and their magnetic properties by electron spin resonance (ESR), magnetic susceptibility, magnetization, and specific heat measurements as well as by density functional theory (DFT) calculations. The Néel temperature TN and the critical field μ0HC needed for the metamagnetic transition increase with x, while the magnetization at a given magnetic field and the Curie–Weiss temperature Θ decrease with x. We show that the tendency for the interlayer antiferromagnetic (AFM) coupling in francisites is not explained by interlayer spin exchange but by the interlayer high-spin orbital interaction that occur across the van der Waals (vdW) gaps, hence indicating that francisites are vdW ferromagnets. This is surprising because, so far, well-established vdW ferromagnets are either layered tellurides or layered iodides. The trends in TN, μ0HC, and the magnetization of Cu3Bi(Se1–xTexO3)2O2Br as a function of x are well explained by the interlayer AFM interactions, and that in the Θ is explained by the intralayer spin exchanges. We proposed how one might modify francisites to make their interlayer interactions ferromagnetic (FM), hence leading to oxide vdW ferromagnets.}, journal={CHEMISTRY OF MATERIALS}, author={Markina, Maria and Vasilchikova, Tatyana and Kuznetsova, Elena and Berdonosov, Peter and Olenev, Andrey and Chung, Seung Hwan and Koo, Hyun-Joo and Whangbo, Myung-Hwan and Vasiliev, Alexander}, year={2022}, month={Dec} } @article{lee_park_shim_whangbo_2022, title={Skin-Deep Aspect of Thermopower in Bi(2)Q(3), PbQ, and BiCuQO (Q = Se, Te): Hidden One-Dimensional Character of Their Band Edges Leading to High Thermopower}, ISSN={["1520-4898"]}, DOI={10.1021/acs.accounts.2c00255}, abstractNote={ConspectusThermoelectric (TE) materials have received much attention because of their ability to convert heat energy to electrical energy. At a given temperature T, the efficiency of a TE material for this energy conversion is measured by the figure of merit zT, which is related to the thermopower (or Seebeck coefficient) S, the thermal conductivity κ, and the electrical conductivity σ of the TE material as zT = (S2σT)/κ. Bi2Q3 and PbQ (Q = Se, Te) are efficient TE materials with high zT, although they are not ecofriendly and their stability is poor at high temperature. In principle, a TE material can have a high zT if it has a low thermal conductivity and a high electrical conductivity, but the latter condition is hardly met in a real material because the parameters S, σ and κ have a conflicting dependence on material properties. The difficulty in searching for TE materials of high zT is even more exasperated because the relationship between the thermopower S and the carrier density n (hereafter, the S-vs-n relationship) for the well-known hole-doped samples of BiCuSeO showed that the hole carriers responsible for their thermopower are associated largely with the electronic states lying within ∼0.5 eV of its valence band maximum (VBM). Thus, the states governing the TE properties lie in the "skin-deep" region from the VBM. For electron-doped TE systems, the electron carriers responsible for their thermopower should also be associated with the electronic states lying within ∼0.5 eV of the conduction band minimum (CBM). This makes it difficult to predict TE materials of high zT. One faces a similar skin-deep phenomenon in searching for superconductors of high transition temperature because the transition from a normal metallic to a superconducting state involves the normal metallic states in the vicinity of the Fermi level EF. Other skin-deep phenomena in metallic compounds include the formation of charge density wave (CDW), which involves the electronic states in the vicinity of their Fermi levels. For magnetic materials of transition-metal ions, the preferred orientation of their spin moments is a skin-deep phenomenon because it is governed by the interaction between the highest-occupied and the lowest unoccupied d-states of these ions. In the present work we probe the issues concerning how to find the possible range of thermopower expected for a given TE material and hence how to recognize what experimental values of thermopower are expected or unusual. For these purposes, we analyze the accumulated S and n data on the three well-studied TE materials, Bi2Q3, PbQ, and BiCuQO (Q = Se, Te), as representative examples, in terms of the ideal theoretical S-vs-n relationships, which we determine for their defect-free Bi2Q3, PbQ, and BiCuQO structures using density functional theory (DFT) calculations under the rigid band approximation. We find that the general trends in the experimental S-vs-n relationships are reasonably well explained by the calculated S-vs-n relationships, and the carrier densities covering these relationships are associated with the states lying within ∼0.5 eV from their band edges confirming the skin-deep nature of their thermoelectric properties. Despite the fact that these TE materials are not one-dimensional (1D) in structure, they mostly possess sharp density-of-state peaks around their band edges because their band dispersions have a hidden 1D character so their thermopower is generally high in magnitude.}, journal={ACCOUNTS OF CHEMICAL RESEARCH}, author={Lee, Changhoon and Park, Taesu and Shim, Ji Hoon and Whangbo, Myung-Hwan}, year={2022}, month={Sep} } @article{whangbo_kremer_koo_2022, title={Unusually High Magnetic Moments Reported for the High-Spin Co2+ Ions at Axially Elongated CoO4X2 (X = Cl, Br, S, Se) Octahedral Sites: Overestimated Magnetic Moments Caused by Underestimated Magnetic Form Factors}, ISSN={["1932-7455"]}, DOI={10.1021/acs.jpcc.2c05586}, abstractNote={An irreconcilable discrepancy between theory and experiment concerning the magnetic moments of the high-spin Co2+ (d7, S = 3/2) ions at the axially elongated CoO4X2 (X = Cl, Br, S, Se) octahedral sites was pointed out in our recent study [ Inorg. Chem. 2020, 59, 18319−18324]. The magnetic moments μobs of the Co2+ ions in materials containing the CoO4X2 units, determined from refinements of powder neutron diffraction patterns collected in their magnetically ordered states, were found to be notably larger than the spin-only moment of 3 μB (namely, 3.22–4.45 μB). Characteristically, the moments increase almost linearly with the bond-length ratio R = rCo–X/rCo–O, despite the fact that the orbital moments of the Co2+ ions are essentially quenched according to theoretical analyses and DFT + U + SOC computations. In this work, we probe the probable cause for the overestimation of magnetic moments in the ordered magnetic structures. We argue that the overestimated magnetic moments of the Co2+ ions and their increase with the bond-length ratio R originate from the underestimated magnetic form factors of the Co2+ ions at the CoO4X2 octahedral sites. The magnetic form factor F(q) of the Co2+ ion in each CoO4X2 octahedron is the Fourier transform of the magnetic moment distribution ρ(r) around the Co2+ ion, which is the electron density distribution associated with the magnetic orbitals (i.e., the singly occupied d-states) of the CoO4X2 octahedron. The conventional implementation of the magnetic form factor in refinement codes employed an approximation with a q-dependence calculated from the atomic wave function of the isolated ion. Since the spin moment distribution of ρ(r) at the axially elongated CoO4X2 (X = Cl, Br, S, Se) octahedral sites is delocalized from the Co2+ sites to its surrounding ligands, the moment distribution becomes anisotropic in shape. Use of the truncated and spherical approximation underestimates the form factor of the Co2+ ion, and its use in neutron diffraction refinements overestimates the magnetic moments. This effect becomes more pronounced as the moment density distribution is more delocalized along the Co–X direction.}, journal={JOURNAL OF PHYSICAL CHEMISTRY C}, author={Whangbo, Myung-Hwan and Kremer, Reinhard K. and Koo, Hyun-Joo}, year={2022}, month={Sep} } @article{luo_xu_xia_pang_xu_whangbo_sun_chen_2021, title={Anomaly Negative Resistance Phenomena in Highly Epitaxial PrBa0.7Ca0.3Co2O5+delta Thin Films Induced from Superfast Redox Reactions}, volume={11}, ISSN={["2073-4344"]}, DOI={10.3390/catal11121441}, abstractNote={Thin films of Ca-doped double perovskite, PrBa0.7Ca0.3Co2O5+δ (PBCC), were epitaxially grown on (001) SrTiO3, and their redox reactions under a switching flow of H2 and O2 gases were examined at various temperatures by measuring the resistance R(t) of the films as a function of the gas flow time t. In the temperature range between 350 and 725 °C, these thin films are reduced and oxidized in an ultrafast manner under the flow of H2 and O2 gases, respectively, suggesting that PBCC thin films are promising candidates for developing ultra-sensitive oxygen sensors or SOFC cathodes at intermediate or high temperatures. When the gas flow is switched to O2, the reduced PBCC thin films exhibit a negative resistance at temperatures above 600 °C but a positive resistance at temperatures below 600 °C. The probable cause for these anomalous transport properties is the diffusion of the H atoms from the cathode to the anode in the PBCC film, which provides a current opposite to that resulting from the external voltage.}, number={12}, journal={CATALYSTS}, author={Luo, Yumei and Xu, Xing and Xia, Yudong and Pang, Shengli and Xu, Fen and Whangbo, Myung-Hwan and Sun, Lixian and Chen, Chonglin}, year={2021}, month={Dec} } @article{xing_zhou_liu_wang_wang_zheng_dai_whangbo_huang_2021, title={Atomically dispersed cobalt-based species anchored on polythiophene as an efficient electrocatalyst for oxygen evolution reaction}, volume={545}, ISSN={["1873-5584"]}, DOI={10.1016/j.apsusc.2021.148943}, abstractNote={For clean and renewable energy conversion systems, it is important to develop efficient, earth-abundant, low-cost and stable electrocatalysts for oxygen evolution reaction (OER). Herein, we prepared an atomically dispersed cobalt coordinated with oxygen and sulfur species on the conductive polymer polythiophene (PTh) via CoS bond as a stable noble-metal-free electrocatalyst for the OER. A novel cobalt-based catalytic site structure, CoxOyS4, is successfully fabricated. The resulting electrocatalyst, [email protected], exhibits an excellent OER performance with overpotential of 338 mV versus reversible hydrogen electrode (RHE) at a current density of 10 mA cm−2 and the Tafel slope of 52 mV dec−1 in alkaline electrolyte. This performance is better than that of the commercial RuO2 and even comparable with the state-of-the-art catalyst IrO2. Our work suggests that the atomically dispersed cobalt-based species decorated PTh may be a good alternative for precious-metal-based catalysts.}, journal={APPLIED SURFACE SCIENCE}, author={Xing, Danning and Zhou, Peng and Liu, Yuanyuan and Wang, Zeyan and Wang, Peng and Zheng, Zhaoke and Dai, Ying and Whangbo, Myung-Hwan and Huang, Baibiao}, year={2021}, month={Apr} } @article{zhao_liu_hu_jia_cui_wu_whangbo_ren_2021, title={Difference in magnetic anisotropy of the ferromagnetic monolayers VI3 and CrI3}, volume={103}, ISSN={["2469-9969"]}, DOI={10.1103/PhysRevB.103.014438}, abstractNote={Concerning the magnetic anisotropy and magnetic moments of the ${M}^{3+}$ $(M=\mathrm{V}, \mathrm{Cr})$ ions in ferromagnetic $(\mathrm{FM}){M\mathrm{I}}_{3}$ monolayers, which have a honeycomb pattern of edge-sharing ${M\mathrm{I}}_{6}$ octahedra, conflicting observations have been reported in experimental and theoretical studies. We resolve these conflicts by determining the magnetic anisotropy energies for the ${M}^{3+}$ ions of ${M\mathrm{I}}_{3}$ monolayers, by analyzing their preferred spin orientations in terms of the selection rules based on the highest occupied molecular orbital--lowest unoccupied molecular orbital interactions of the ${M\mathrm{I}}_{6}$ octahedra, and by discussing whether or not the ${M}^{3+}$ ions are uniaxial. Here we show that the FM monolayer ${\mathrm{VI}}_{3}$ is uniaxial, but that of ${\mathrm{CrI}}_{3}$ is not. The magnetic anisotropy energy for the ${\mathrm{V}}^{3+}({d}^{2},S=1)$ ion of ${\mathrm{VI}}_{3}$ is greater than that for the ${\mathrm{Cr}}^{3+}$ $({d}^{3},$ $S=3/2)$ ion of ${\mathrm{CrI}}_{3}$ by more than an order of magnitude (i.e., \ensuremath{\sim}8 vs \ensuremath{\sim}0.6 meV). The ${\mathrm{V}}^{3+}$ ion exhibits uniaxial magnetism because its orbital quantum number L is not zero $(L=\phantom{\rule{0.16em}{0ex}}1)$, in contrast to the ${\mathrm{Cr}}^{3+}$ ion $(L=0)$.}, number={1}, journal={PHYSICAL REVIEW B}, author={Zhao, Guo-Dong and Liu, Xingen and Hu, Tao and Jia, Fanhao and Cui, Yaning and Wu, Wei and Whangbo, Myung-Hwan and Ren, Wei}, year={2021}, month={Jan} } @article{luo_xu_cheng_li_huang_whangbo_deng_hong_2021, title={High partial thermal conductivity of luminescence sites: a crucial factor for reducing the heat-induced lowering of the luminescence efficiency}, ISSN={["2050-7534"]}, DOI={10.1039/d1tc02287c}, abstractNote={The high partial thermal conductivity of luminescence sites is associated with the reduction of the heat-induced lowering of the luminescence efficiency of phosphors. This finding may be helpful for screening efficient phosphors.}, journal={JOURNAL OF MATERIALS CHEMISTRY C}, author={Luo, Ni and Xu, Jing and Cheng, Xiyue and Li, ZhenHua and Huang, Yidong and Whangbo, Myung-Hwan and Deng, Shuiquan and Hong, Maochun}, year={2021}, month={Sep} } @article{etourneau_delmas_jobic_whangbo_2021, title={In Honor of John Bannister Goodenough, an Outstanding Visionary}, volume={26}, ISSN={["1420-3049"]}, DOI={10.3390/molecules26216624}, abstractNote={John B [...].}, number={21}, journal={MOLECULES}, author={Etourneau, Jean and Delmas, Claude and Jobic, Stephane and Whangbo, Myung-Hwan}, year={2021}, month={Nov} } @misc{whangbo_koo_kremer_2021, title={Spin Exchanges between Transition Metal Ions Governed by the Ligand p-Orbitals in Their Magnetic Orbitals}, volume={26}, ISSN={["1420-3049"]}, DOI={10.3390/molecules26030531}, abstractNote={In this review on spin exchanges, written to provide guidelines useful for finding the spin lattice relevant for any given magnetic solid, we discuss how the values of spin exchanges in transition metal magnetic compounds are quantitatively determined from electronic structure calculations, which electronic factors control whether a spin exchange is antiferromagnetic or ferromagnetic, and how these factors are related to the geometrical parameters of the spin exchange path. In an extended solid containing transition metal magnetic ions, each metal ion M is surrounded with main-group ligands L to form an MLn polyhedron (typically, n = 3–6), and the unpaired spins of M are represented by the singly-occupied d-states (i.e., the magnetic orbitals) of MLn. Each magnetic orbital has the metal d-orbital combined out-of-phase with the ligand p-orbitals; therefore, the spin exchanges between adjacent metal ions M lead not only to the M–L–M-type exchanges, but also to the M–L…L–M-type exchanges in which the two metal ions do not share a common ligand. The latter can be further modified by d0 cations A such as V5+ and W6+ to bridge the L…L contact generating M–L…A…L–M-type exchanges. We describe several qualitative rules for predicting whether the M–L…L–M and M–L…A…L–M-type exchanges are antiferromagnetic or ferromagnetic by analyzing how the ligand p-orbitals in their magnetic orbitals (the ligand p-orbital tails, for short) are arranged in the exchange paths. Finally, we illustrate how these rules work by analyzing the crystal structures and magnetic properties of four cuprates of current interest: α-CuV2O6, LiCuVO4, (CuCl)LaNb2O7, and Cu3(CO3)2(OH)2.}, number={3}, journal={MOLECULES}, author={Whangbo, Myung-Hwan and Koo, Hyun-Joo and Kremer, Reinhard K.}, year={2021}, month={Feb} } @misc{li_yu_lou_feng_whangbo_xiang_2021, title={Spin Hamiltonians in Magnets: Theories and Computations}, volume={26}, ISSN={["1420-3049"]}, DOI={10.3390/molecules26040803}, abstractNote={The effective spin Hamiltonian method has drawn considerable attention for its power to explain and predict magnetic properties in various intriguing materials. In this review, we summarize different types of interactions between spins (hereafter, spin interactions, for short) that may be used in effective spin Hamiltonians as well as the various methods of computing the interaction parameters. A detailed discussion about the merits and possible pitfalls of each technique of computing interaction parameters is provided.}, number={4}, journal={MOLECULES}, author={Li, Xueyang and Yu, Hongyu and Lou, Feng and Feng, Junsheng and Whangbo, Myung-Hwan and Xiang, Hongjun}, year={2021}, month={Feb} } @article{koo_kremer_whangbo_2021, title={Unusual Spin Exchanges Mediated by the Molecular Anion P2S64-: Theoretical Analyses of the Magnetic Ground States, Magnetic Anisotropy and Spin Exchanges of MPS3 (M = Mn, Fe, Co, Ni)}, volume={26}, ISSN={["1420-3049"]}, DOI={10.3390/molecules26051410}, abstractNote={We examined the magnetic ground states, the preferred spin orientations and the spin exchanges of four layered phases MPS3 (M = Mn, Fe, Co, Ni) by first principles density functional theory plus onsite repulsion (DFT + U) calculations. The magnetic ground states predicted for MPS3 by DFT + U calculations using their optimized crystal structures are in agreement with experiment for M = Mn, Co and Ni, but not for FePS3. DFT + U calculations including spin-orbit coupling correctly predict the observed spin orientations for FePS3, CoPS3 and NiPS3, but not for MnPS3. Further analyses suggest that the ||z spin direction observed for the Mn2+ ions of MnPS3 is caused by the magnetic dipole–dipole interaction in its magnetic ground state. Noting that the spin exchanges are determined by the ligand p-orbital tails of magnetic orbitals, we formulated qualitative rules governing spin exchanges as the guidelines for discussing and estimating the spin exchanges of magnetic solids. Use of these rules allowed us to recognize several unusual exchanges of MPS3, which are mediated by the symmetry-adapted group orbitals of P2S64− and exhibit unusual features unknown from other types of spin exchanges.}, number={5}, journal={MOLECULES}, author={Koo, Hyun-Joo and Kremer, Reinhard and Whangbo, Myung-Hwan}, year={2021}, month={Mar} } @article{myung-hwan_mao-chun_shui-quan_2020, title={Atom Response Theory of Nonlinear Optical Responses and Its Applications}, volume={39}, ISSN={["0254-5861"]}, DOI={10.14102/j.cnki.0254-5861.2011-3019}, number={12}, journal={CHINESE JOURNAL OF STRUCTURAL CHEMISTRY}, author={Myung-Hwan, Whangbo and Mao-Chun, Hong and Shui-Quan, Deng}, year={2020}, month={Dec}, pages={2172–2181} } @article{gao_wu_liang_wang_zheng_wang_liu_dai_whangbo_huang_2020, title={Cu2O Nanoparticles with Both {100} and {111} Facets for Enhancing the Selectivity and Activity of CO2 Electroreduction to Ethylene}, volume={7}, ISSN={["2198-3844"]}, DOI={10.1002/advs.201902820}, abstractNote={Cu2O nanoparticles (NPs) enclosed with different crystal facets, namely, c-Cu2O NPs with {100} facets, o-Cu2O NPs with {111} facets, and t-Cu2O NPs with both {111} and {100} facets, are prepared and their electrocatalytic properties for the reduction of CO2 to C2H4 are evaluated. It is shown that the selectivity and activity of the C2H4 production depend strongly on the crystal facets exposed in Cu2O NPs. The selectivities for the C2H4 production increases in the order, c-Cu2O < o-Cu2O < t-Cu2O, (with FEC2H4 = 38%, 45%, and 59%, respectively). This study suggests that Cu2O NPs are more likely responsible for the selectivity and activity for the C2H4 production than the metallic Cu NPs produced on the surface of Cu2O NPs. This work provides a new route for enhancing the selectivity of the electrocatalytic CO2 reduction by crystal facet engineering.}, number={6}, journal={ADVANCED SCIENCE}, author={Gao, Yugang and Wu, Qian and Liang, Xizhuang and Wang, Zeyan and Zheng, Zhaoke and Wang, Peng and Liu, Yuanyuan and Dai, Ying and Whangbo, Myung-Hwan and Huang, Baibiao}, year={2020}, month={Mar} } @article{wang_wang_zhang_jiang_bao_cheng_zheng_wang_liu_whangbo_et al._2020, title={Enhancing the Photoelectrochemical Water Oxidation Reaction of BiVO4 Photoanode by Employing Carbon Spheres as Electron Reservoirs}, volume={10}, ISSN={["2155-5435"]}, DOI={10.1021/acscatal.0c03671}, abstractNote={The rate-determining step of the photoelectrochemical (PEC) water splitting is the water oxidation reaction at the photoanode, which is 4 orders of magnitude slower than the water reduction reaction at the photocathode. In a conventional process to accelerate the water oxidation, oxygen evolution cocatalysts (OECs) are usually used on the surface of a photoanode. As an alternative strategy, we considered employing a composite photoanode made up of a semiconductor and carbon spheres, for it is expected that the photogenerated electrons on the semiconductor particles can be captured by the carbon spheres as electron reservoirs and leave the photogenerated holes on the surface of the semiconductor particles, which promotes the effective separation of photogenerated electrons and holes. More importantly, the holes accumulated in the valence band accelerate the water oxidation reaction rate with the rapid release of electrons stored on the carbon sphere. Therefore, the composite photoanode achieves a higher photocurrent at a lower applied bias. We provide a proof of concept for this strategy by preparing a composite photoanode by combining bismuth vanadium oxide BiVO4 with carbon spheres and find that the resulting photoanode displays a remarkable enhancement in the rate of the photoanode water oxidation.}, number={21}, journal={ACS CATALYSIS}, author={Wang, Minrui and Wang, Zeyan and Zhang, Bo and Jiang, Weiyi and Bao, Xiaolei and Cheng, Hefeng and Zheng, Zhaoke and Wang, Peng and Liu, Yuanyuan and Whangbo, Myung-Hwan and et al.}, year={2020}, month={Nov}, pages={13031–13039} } @article{wang_mao_niu_shen_whangbo_huang_dai_2020, title={Ferromagnetic dual topological insulator in a two-dimensional honeycomb lattice}, volume={7}, ISSN={["2051-6355"]}, DOI={10.1039/d0mh00803f}, abstractNote={Magnetic topological insulators (TIs), including the quantum anomalous Hall effect and antiferromagnetic TIs, have attracted significant attention owing to the exotic properties they give rise to, however, ferromagnetic TIs with gapless surface/edge states and a nonzero topological invariant have not been reported so far.}, number={9}, journal={MATERIALS HORIZONS}, author={Wang, Hao and Mao, Ning and Niu, Chengwang and Shen, Shiying and Whangbo, Myung-Hwan and Huang, Baibiao and Dai, Ying}, year={2020}, month={Sep}, pages={2431–2438} } @article{zvereva_raganyan_vasilchikova_nalbandyan_gafurov_vavilova_zakharov_koo_pomjakushin_susloparova_et al._2020, title={Hidden magnetic order in the triangular-lattice magnet Li2MnTeO6}, volume={102}, ISSN={["2469-9969"]}, DOI={10.1103/PhysRevB.102.094433}, abstractNote={The manganese tellurate ${\mathrm{Li}}_{2}{\mathrm{MnTeO}}_{6}$ consists of trigonal spin lattices made up of ${\mathrm{Mn}}^{4+}$ (${d}^{3}$, $S=3/2$) ions. The magnetic properties of this compound were characterized by several experimental techniques, which include magnetic susceptibility, specific-heat, dielectric permittivity, electron-spin-resonance, nuclear magnetic resonance (NMR), and neutron powder-diffraction measurements, and by density functional theory calculations. The magnetic susceptibility $\ensuremath{\chi}(T)$ demonstrates very unusual behavior. It is described by the Curie-Weiss law at high temperature with Curie-Weiss temperature of $\mathrm{\ensuremath{\Theta}}=\ensuremath{-}74\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ and exhibits no obvious anomaly indicative of a long-range magnetic ordering at low magnetic fields. At high magnetic fields, however, the character of $\ensuremath{\chi}(T)$ changes showing a maximum at about 9 K. That this maximum of $\ensuremath{\chi}(T)$ reflects the onset of an antiferromagnetic order was confirmed by specific-heat measurements, which exhibit a clear $\ensuremath{\lambda}$-type anomaly at ${T}_{\mathrm{N}}\ensuremath{\approx}8.5\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ even at zero magnetic field, and by $^{7}\mathrm{Li}$ NMR and dielectric permittivity measurements. The magnetic structure of ${\mathrm{Li}}_{2}{\mathrm{MnTeO}}_{6}$, determined by neutron powder-diffraction measurements at 1.6 K, is described by the ${120}^{\ensuremath{\circ}}$ noncollinear spin structure with the propagation vector $\mathbit{k}=(1/3,\phantom{\rule{0.28em}{0ex}}1/3,\phantom{\rule{0.28em}{0ex}}0)$. Consistent with this finding, the spin-exchange interactions evaluated for ${\mathrm{Li}}_{2}{\mathrm{MnTeO}}_{6}$ by density functional calculations are dominated by the nearest-neighbor antiferromagnetic exchange within each triangular spin lattice. This spin lattice is strongly spin frustrated with $f=|\mathrm{\ensuremath{\Theta}}|/{T}_{\mathrm{N}}\ensuremath{\approx}8$ and exhibits a two-dimensional magnetic character in a broad temperature range above ${T}_{\mathrm{N}}$.}, number={9}, journal={PHYSICAL REVIEW B}, author={Zvereva, E. A. and Raganyan, G. and Vasilchikova, T. M. and Nalbandyan, V. B. and Gafurov, D. A. and Vavilova, E. L. and Zakharov, K. and Koo, H-J and Pomjakushin, V. Yu and Susloparova, A. E. and et al.}, year={2020}, month={Sep} } @article{li_ni_li_koo_whangbo_feng_xiang_2020, title={Intralayer ferromagnetism between S=5/2 ions in MnBi2Te4: Role of empty Bi p states}, volume={101}, ISSN={["2469-9969"]}, DOI={10.1103/PhysRevB.101.201408}, abstractNote={The layered magnetic topological insulator MnBi$_2$Te$_4$ is a promising platform to realize the quantum anomalous Hall effect because its layers possess intrinsic ferromagnetism. However, it is not well understood why the high-spin $d^5$ magnetic ions Mn$^{2+}$ forming the Mn-Te-Mn spin exchange paths prefer ferromagnetic (FM) coupling, contrary to the prediction of the Goodenough-Kanamori rule that a TM-L-TM spin exchange, where TM and L are a transition-metal magnetic cation and a main group ligand, respectively, is antiferromagnetic (AFM) even when the bond angle of the exchange path is 90$^{\circ}$. Using density functional theory (DFT) calculations, we show that the presence of Bi$^{3+}$ ions is essential for the FM coupling in MnBi$_2$Te$_4$. Then, using a tight-binding model Hamiltonian, we find that high-spin $d^5$ ions (S = 5/2) in TM-L-TM spin exchange paths prefer FM coupling if the empty p-orbitals of a nonmagnetic cation M (e.g., Bi$^{3+}$ ion) hybridize strongly with those of the bridging ligand L, but AFM coupling otherwise.}, number={20}, journal={PHYSICAL REVIEW B}, author={Li, Jing and Ni, J. Y. and Li, X. Y. and Koo, H-J and Whangbo, M-H and Feng, J. S. and Xiang, H. J.}, year={2020}, month={May} } @article{cheng_li_wu_hong_whangbo_deng_2020, title={Key Factors Controlling the Large Second Harmonic Generation in Nonlinear Optical Materials}, volume={12}, ISSN={["1944-8252"]}, DOI={10.1021/acsami.9b20023}, abstractNote={The second harmonic generation (SHG) responses of nonisostructural nonlinear optical (NLO) compounds, β-BaB2O4, LiB3O5, CsB3O5, CsLiB6O10, KBe2BO3F2, and LiCs2PO4, were examined by density functional theory (DFT) calculations, and the contributions of their individual cations and anions were determined by performing atomic response theory analyses. In all of these compounds, the contribution of all metal cations lies in the range of ∼9.3 to ∼29.7% of the total SHG responses, and that of all anions lies between ∼57.4 and ∼72.3%. However, in terms of individual atom contribution, a large metal cation can contribute more than does an anion to the total SHG response. Our work shows that the SHG contribution of an individual anion (e.g., O2–) is weakened when it forms covalent bonds with its surrounding cations (e.g., O–B). The contribution of an individual cation is further affected by the homogeneity of its surrounding anion distribution and also by how strongly the polarizabilities of its surrounding anions are weakened by covalent bonding with other cations. The SHG response increases with αsum/(NEg), an important parameter useful in searching for new NLO materials, where αsum is the sum of the polarizabilities of all of the ions in the primitive unit cell, N is the total number of atoms per primitive cell, and Eg is the band gap.}, number={8}, journal={ACS APPLIED MATERIALS & INTERFACES}, author={Cheng, Xiyue and Li, ZhenHua and Wu, Xin-Tao and Hong, Maochun and Whangbo, Myung-Hwan and Deng, Shuiquan}, year={2020}, month={Feb}, pages={9434–9439} } @article{yang_hu_wu_whangbo_radaelli_stroppa_2020, title={Magneto-Optical Kerr Switching Properties of (CrI3)(2) and (CrBr3/CrI3) Bilayers}, volume={2}, ISSN={["2637-6113"]}, DOI={10.1021/acsaelm.0c00154}, abstractNote={We explore the magneto-optical Kerr effect (MOKE) for different spin configurations of the (CrI3)2 bilayer and (CrBr3/CrI3) mixed bilayer using symmetry arguments and first-principles electronic structure calculations. Starting from CrX3 (X = I, Br) monolayers, we considered collinear ferromagnetic (FM) and layered antiferromagnetic (AFM) states for (CrI3)2 and (CrBr3/CrI3) bilayers. The AFM (CrI3)2 bilayer does not show MOKE, consistent with the presence of a symmetry operator combining inversion (I) and time reversal (T) symmetries. The FM state preserves I symmetry but breaks the T symmetry, thus allowing a nonzero Kerr angle, which is reversible by switching the FM spins. The (CrBr3/CrI3) bilayer breaks both the I and T symmetries and thus exhibits MOKE both in the FM state and, remarkably, in the AFM state. In both FM and AFM configurations, the Kerr angle switches by reversing the spins in both layers. Our study demonstrates that the MOKE spectra can help to characterize different magnetic configurations in these emerging two-dimensional (2D) magnetic materials due to a different stacking of the monolayers, even in the AFM case. Note that the present symmetry analyses and MOKE properties apply to more general 2D magnetic van der Waals heterostructures. Furthermore, we propose the (CrBr3/CrI3) bilayer as a promising candidate for AFM spintronics since the two time-reversed AFM states are associated with opposite Kerr rotation, i.e., they could be used as memory elements.}, number={5}, journal={ACS APPLIED ELECTRONIC MATERIALS}, author={Yang, Ke and Hu, Wentao and Wu, Hua and Whangbo, Myung-Hwan and Radaelli, Paolo Giuseppe and Stroppa, Alessandro}, year={2020}, month={May}, pages={1373–1380} } @article{wang_lv_zhou_liang_wang_liu_wang_zheng_dai_li_et al._2020, title={Molybdenum Nitride Electrocatalysts for Hydrogen Evolution More Efficient than Platinum/Carbon: Mo2N/CeO2@Nickel Foam}, volume={12}, ISSN={["1944-8252"]}, DOI={10.1021/acsami.0c02851}, abstractNote={To produce hydrogen economically by electrolysis of water, one needs to develop a non-precious-metal catalyst that is as efficient as platinum metal. Here, we prepare such a catalyst by growing a layer of Mo2N over a layer of CeO2 deposited on nickel foam (NF) [hereafter, Mo2N /CeO2@NF] and show that the activity of this self-supported catalyst for hydrogen evolution in 1.0 M KOH is more efficient than that of the Pt/C electrode, achieving a current density of 10 mA/cm2 at a fairly low overpotential of 26 mV. Furthermore, after a long-time electrochemical stability test for 24 h at a fixed current density, the overpotential needed to attain a current density of 10 mA/cm2 is increased only by 6 mV, implying the huge potential of this method to prepare a super HER activity electrode for water splitting.}, number={26}, journal={ACS APPLIED MATERIALS & INTERFACES}, author={Wang, Cong and Lv, Xingshuai and Zhou, Peng and Liang, Xizhuang and Wang, Zeyan and Liu, Yuanyuan and Wang, Peng and Zheng, Zhaoke and Dai, Ying and Li, Yingjie and et al.}, year={2020}, month={Jul}, pages={29153–29161} } @article{koo_shankar_orlandi_sundaresan_whangbo_2020, title={On Ferro- and Antiferro-Spin-Density Waves Describing the Incommensurate Magnetic Structure of NaYNiWO6}, volume={59}, ISSN={["1520-510X"]}, DOI={10.1021/acs.inorgchem.0c02651}, abstractNote={The incommensurate magnetic structure (0.47, 0, 0.49) of NaYNiWO6 exhibits unconventional spin-density waves (SDWs) along the [100] direction, in which up and down spins alternate in each half-wave. This is in contrast to conventional SDWs, in which only one type of spin is present in each half-wave. We probed the formation of these unconventional SDWs by evaluating the spin exchanges of NaYNiWO6 based on density functional theory calculations and analyzing the nature of the spin frustration in NaYNiWO6 and by noting that a SDW is a superposition of two cycloids of opposite chirality. The unconventional SDWs along the [100] direction originate from the spin-frustrated antiferromagnetic chains of Ni2+ ions along that direction, leading to conventional SDWs along the [101] direction and unconventional SDWs along the [001] direction.}, number={24}, journal={INORGANIC CHEMISTRY}, author={Koo, Hyun-Joo and Shankar, Ravi P. N. and Orlandi, Fabio and Sundaresan, Athinarayanan and Whangbo, Myung-Hwan}, year={2020}, month={Dec}, pages={17856–17859} } @article{koo_kremer_whangbo_2020, title={Orbital Magnetic Moments of the High-Spin Co2+ Ions at Axially-Elongated Octahedral Sites: Unquenched as Reported from Experiment or Quenched as Predicted by Theory?}, volume={59}, ISSN={["1520-510X"]}, DOI={10.1021/acs.inorgchem.0c02929}, abstractNote={Neutron diffraction studies on magnetic solids composed of axially elongated CoO4X2 (X = Cl, Br, S, Se) octahedra show that the ordered magnetic moments of their high-spin Co2+ (d7, S = 3/2) ions are greater than 3 μB, i.e., the spin moment expected for S = 3/2 ions, and increase almost linearly from 3.22 to 4.45 μB as the bond-length ratio rCo–X/rCo–O increases from 1.347 to 1.659 where rCo–X and rCo–O are the Co–X and Co–O bond lengths, respectively. These observations imply that the orbital moments of the Co2+ ions increase linearly from 0.22 to 1.45 μB with increasing the rCo–X/rCo–O ratio from 1.347 to 1.659. We probed this implication by examining the condition for unquenched orbital moment and also by evaluating the magnetic moments of the Co2+ ions based on DFT+U+SOC calculations for those systems of the CoO4X2 octahedra. Our work shows that the orbital moments of the Co2+ ions are essentially quenched and, hence, that the observations of the neutron diffraction studies are not explained by the current theory of magnetic moments. This discrepancy between experiment and theory urges one to check the foundations of the current theory of magnetic moments as well as the current method of neutron diffraction refinements for ordered magnetic structures.}, number={24}, journal={INORGANIC CHEMISTRY}, author={Koo, Hyun-Joo and Kremer, Reinhard K. and Whangbo, Myung-Hwan}, year={2020}, month={Dec}, pages={18319–18324} } @article{vasilchikova_nalbandyan_shukaev_koo_whangbo_lozitskiy_bogaychuk_kuzmin_tagirov_vavilova_et al._2020, title={Peculiarities of magnetic ordering in the S=5/2 two-dimensional square-lattice antimonate NaMnSbO4}, volume={101}, ISSN={["2469-9969"]}, DOI={10.1103/PhysRevB.101.054435}, abstractNote={An orthorhombic compound, $\mathrm{NaMnSb}{\mathrm{O}}_{4}$, represents a square net of magnetic $\mathrm{M}{\mathrm{n}}^{2+}$ ions residing in vertex-shared oxygen octahedra. Its static and dynamic magnetic properties were studied using magnetic susceptibility, specific heat, magnetization, electron spin resonance (ESR), nuclear magnetic resonance (NMR), and density-functional calculations. Thermodynamic data indicate an establishment of the long-range magnetic order with ${T}_{\mathrm{N}}\ensuremath{\sim}44\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, which is preceded by a short-range one at about 55 K. In addition, a nontrivial wasp-waisted hysteresis loop of the magnetization was observed, indicating that the ground state is most probably canted antiferromagnetic. Temperature dependence of the magnetic susceptibility is described reasonably well in the framework of two-dimensional square-lattice model with the main exchange parameter $J=\ensuremath{-}5.3\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, which is in good agreement with density-functional analysis, NMR, and ESR data.}, number={5}, journal={PHYSICAL REVIEW B}, author={Vasilchikova, Tatyana and Nalbandyan, Vladimir and Shukaev, Igor and Koo, Hyun-Joo and Whangbo, Myung-Hwan and Lozitskiy, Andrey and Bogaychuk, Alexander and Kuzmin, Vyacheslav and Tagirov, Murat and Vavilova, Evgeniya and et al.}, year={2020}, month={Feb} } @article{maggard_chen_deng_whangbo_2020, title={Physical Properties of Molecules and Condensed Materials Governed by Onsite Repulsion, Spin-Orbit Coupling and Polarizability of their Constituent Atoms}, volume={25}, ISSN={["1420-3049"]}, url={https://www.mdpi.com/1420-3049/25/4/867}, DOI={10.3390/molecules25040867}, abstractNote={The onsite repulsion, spin–orbit coupling and polarizability of elements and their ions play important roles in controlling the physical properties of molecules and condensed materials. In celebration of the 150th birthday of the periodic table this year, we briefly review how these parameters affect the physical properties and are interrelated.}, number={4}, journal={Molecules}, author={Maggard, P.A. and Chen, X. and Deng, S. and Whangbo, M}, year={2020}, pages={867} } @article{jia_cheng_whangbo_hong_deng_2020, title={Second harmonic generation responses of KH2PO4: importance of K and breaking down of Kleinman symmetry}, volume={10}, ISSN={["2046-2069"]}, DOI={10.1039/d0ra03136d}, abstractNote={The second harmonic generation (SHG) responses of the paraelectric and ferroelectric phases of KH2PO4 (KDP) were calculated by first-principles density functional theory (DFT) calculations, and the individual atom contributions to the SHG responses were analyzed by the atom response theory (ART). We show that the occurrence of static polarization does not enhance the SHG responses of the ferroelectric KDP, and that the Kleinman symmetry is reasonably well obeyed for the paraelectric phase, but not for the ferroelectric phase despite that the latter has a larger bandgap. This is caused most likely by the fact that the ferroelectric phase has lower-symmetry local structures than does the paraelectric phase. The contribution to the SHG response of an individual K+ ion is comparable to that of an individual O2- ion. The contributions of the O2- and K+ ions arise overwhelmingly from the polarizable parts of the electronic structure, namely, from the valence bands of the O-2p nonbonding states and from the conduction bands of the K-3d states.}, number={44}, journal={RSC ADVANCES}, author={Jia, Minghao and Cheng, Xiyue and Whangbo, Myung-Hwan and Hong, Maochun and Deng, Shuiquan}, year={2020}, month={Jul}, pages={26479–26485} } @article{sorolla_wang_koo_whangbo_jacobson_2020, title={Synthesis of the Elusive S=1/2 Star Structure: A Possible Quantum Spin Liquid Candidate}, volume={142}, ISSN={["1520-5126"]}, DOI={10.1021/jacs.0c00901}, abstractNote={Materials with two-dimensional, geometrically frustrated, spin-1/2 lattices provide a fertile playground for the study of intriguing magnetic phenomena such as quantum spin liquid (QSL) behavior, but their preparation has been a challenge. In particular, the long-sought, exotic spin-1/2 star structure has not been experimentally realized to date. Here we report the synthesis of [(CH3)2(NH2)]3[CuII3(μ3-OH)(μ3-SO4)(μ3-SO4)3]·0.24H2O with an S = 1/2 star lattice. On the basis of the magnetic susceptibility and heat capacity measurements, the layered Cu-based compound exhibits antiferromagnetic interactions but no magnetic ordering or spin freezing down to 2 K. The spin-frustrated material appears to be a promising QSL candidate.}, number={11}, journal={JOURNAL OF THE AMERICAN CHEMICAL SOCIETY}, author={Sorolla, Maurice, II and Wang, Xiqu and Koo, Hyun-Joo and Whangbo, Myung-Hwan and Jacobson, Allan J.}, year={2020}, month={Mar}, pages={5013–5016} } @article{lee_kim_son_shim_whangbo_2020, title={Ternary selenides A(2)Sb(4)Se(8) (A = K, Rb and Cs) as an n-type thermoelectric material with high power factor and low lattice thermal conductivity: importance of the conformationally flexible Sb-Se-Se-Sb bridges}, volume={10}, ISSN={["2046-2069"]}, DOI={10.1039/d0ra01751e}, abstractNote={We investigated the thermoelectric properties of the layered ternary selenides A2Sb4Se8 (A = K, Rb and Cs) and the lattice thermal conductivity of K2Sb4Se8 on the basis of DFT calculations, to find that these selenides are a high-performance n-type thermoelectric material. The Seebeck coefficients and power factors calculated for the electron carriers of A2Sb4Se8 (A = K, Rb and Cs) are greater than those of the well-known thermoelectric materials Bi2Te3 and PbTe. The lattice thermal conductivity κlatt of K2Sb4Se8 is comparable to that of PbTe, well-known for its low lattice thermal conductivity. In terms of both electronic and phonon structures, the structural parts of the A2Sb4Se8 (A = K, Rb and Cs) phases crucial for their thermoelectric properties are the conformationally-flexible Sb-Se-Se-Sb bridges that interlink between their structurally rigid units.}, number={24}, journal={RSC ADVANCES}, author={Lee, Changhoon and Kim, Sujee and Son, Won-Joon and Shim, Ji-Hoon and Whangbo, Myung-Hwan}, year={2020}, month={Apr}, pages={14415–14421} } @article{cai_cheng_whangbo_hong_deng_2020, title={The partition principles for atomic-scale structures and their physical properties: application to the nonlinear optical crystal material KBe2BO3F2}, volume={22}, ISSN={["1463-9084"]}, DOI={10.1039/d0cp02755c}, abstractNote={In implementing the materials genome approach to search for new materials with interesting properties or functions, it is necessary to find the correct functional motif. To this end, it is common to partition an extended structure into various building units and then partition its properties to find the appropriate functional motif. We have developed the general principles for partitioning a structure and its properties in terms of a set of atoms and bonds by analyzing the differential cross-sections of neutron and X-ray scattering phenomena and proposed the procedures with which to partition an extended structure and its properties. We demonstrate how these procedures work by analyzing the nonlinear optical crystal KBe2BO3F2. Our partitioning analysis of KBe2BO3F2 leads to the conclusion that the second harmonic generation response of KBe2BO3F2 is dominated by the ionically bonded metal-centered groups.}, number={34}, journal={PHYSICAL CHEMISTRY CHEMICAL PHYSICS}, author={Cai, Zewen and Cheng, Xiyue and Whangbo, Myung-Hwan and Hong, Maochun and Deng, Shuiquan}, year={2020}, month={Sep}, pages={19299–19306} } @article{golubev_nuss_kremer_gordon_whangbo_ritter_weber_wessel_2020, title={Two-dimensional magnetism in alpha-CuV2O6}, volume={102}, ISSN={["2469-9969"]}, DOI={10.1103/PhysRevB.102.014436}, abstractNote={Several previous studies reported that a one-dimensional Heisenberg chain model is inadequate in describing the magnetic properties of the low-dimensional quantum antiferromagnet $\ensuremath{\alpha}\text{\ensuremath{-}}{\mathrm{CuV}}_{2}{\mathrm{O}}_{6}$, but the origin for this observation has remained unclear. We have reinvestigated the magnetic properties of $\ensuremath{\alpha}\text{\ensuremath{-}}{\mathrm{CuV}}_{2}{\mathrm{O}}_{6}$ and found that our anisotropic magnetic susceptibility, neutron-powder diffraction, and electron paramagnetic spin-resonance measurements are in good agreement with extensive density-functional theory ($\mathrm{DFT}+U$) total energy calculations which indicate that the correct spin lattice model for $\ensuremath{\alpha}\text{\ensuremath{-}}{\mathrm{CuV}}_{2}{\mathrm{O}}_{6}$ is rather a $S=1/2$ 2D-Heisenberg antiferromagnetic lattice. The magnetic susceptibility data are well described by a rectangular Heisenberg antiferromagnet with anisotropy ratio $\ensuremath{\alpha}\ensuremath{\sim}$ 0.7 consistent with the DFT results. Quantum Monte Carlo simulations of the magnetic susceptibilities for a rectangular lattice Heisenberg antiferromagnet were performed in the anisotropy range 0.5 $\ensuremath{\le}\ensuremath{\alpha}\ensuremath{\le}$ 1.0. The results of the Quantum Monte Carlo calculations were cast into a Pad\'e approximant which was used to fit the temperature-dependent magnetic susceptibility data. Neutron-powder-diffraction measurements were used to conclusively solve the collinear antiferromagnetic structure of $\ensuremath{\alpha}\text{\ensuremath{-}}{\mathrm{CuV}}_{2}{\mathrm{O}}_{6}$ below the N\'eel temperature of $\ensuremath{\sim}22.4$ K.}, number={1}, journal={PHYSICAL REVIEW B}, author={Golubev, A. M. and Nuss, J. and Kremer, R. K. and Gordon, E. E. and Whangbo, M-H and Ritter, C. and Weber, L. and Wessel, S.}, year={2020}, month={Jul} } @article{cheng_whangbo_hong_deng_2019, title={Dependence of the Second-Harmonic Generation Response on the Cell Volume to Band-Gap Ratio}, volume={58}, ISSN={["1520-510X"]}, DOI={10.1021/acs.inorgchem.9b01368}, abstractNote={The second-harmonic generation (SHG) coefficients of 12 nonlinear optical chalcopyrites, ABC2 (A = Zn, Cd; B = Si, Ge, Sn; C = P, As) were calculated by first-principles methods to find that given the primitive cell volume V and the band gap Eg of ABC2, the SHG coefficients dav of ABC2 increase almost linearly with increasing value of V/Eg. This suggests that a noncentrosymmetric crystal has a large SHG response when it consists of large atoms, leading to a small band gap.}, number={15}, journal={INORGANIC CHEMISTRY}, author={Cheng, Xiyue and Whangbo, Myung-Hwan and Hong, Maochun and Deng, Shuiquan}, year={2019}, month={Aug}, pages={9572–9575} } @article{koo_whangbo_2019, title={Effect of Nonmagnetic Ion Deficiency on Magnetic Structure: Density Functional Study of Sr2MnO2Cu2-xTe2, Sr2MO2Cu2Te2 (M = Co, Mn), and the Oxide-Hydrides Sr2VO3H, Sr3V2O5H2, and SrVO2H}, volume={58}, ISSN={["1520-510X"]}, DOI={10.1021/acs.inorgchem.9b02456}, abstractNote={Two seemingly puzzling observations on two magnetic systems were analyzed. For the oxide-hydrides Sr2VO3H, Sr3V2O5H2, and SrVO2H, made up of VO4H2 octahedra, the spin orientations of the V3+ (d2, S = 1) ions were reported to be different, namely, perpendicular to the H-V-H bond in Sr2VO3H but parallel to the H-V-H bond in Sr3V2O5H2 and SrVO2H, despite that the d-state split patterns of the VO4H2 octahedra are similar in the three oxide-hydrides. Another puzzling observation is the contrasting magnetic structures of Sr2CoO2Cu2Te2 and Sr2MnO2Cu1.58Te2, consisting of the layers made up of corner-sharing MO4Te2 (M = Co, Mn) octahedra. The Co2+ spins in each CoO2Te2 layer are antiferromagnetically coupled with spins perpendicular to the Te–Co–Te bond, whereas the Mn3+/Mn2+ ions of each MnO2Te2 layer are ferromagnetically coupled with spins parallel to the Te-Mn-Te bonds. We investigated the cause for these observations by performing first-principles density functional theory (DFT) calculations for stoichiometric phases Sr2VO3H, Sr3V2O5H2, SrVO2H, Sr2CoO2Cu2Te2, and Sr2MnO2Cu2Te2, as well as nonstoichiometric phase Sr2MnO2Cu1.5Te2. Our study reveals that the V3+ ions in all three oxide-hydrides should have the spin orientation parallel to the H–V–H bond. The unusual magnetic structure of the MnO2Te2 layers of Sr2MnO2Cu1.52Te2 arises from the preference of a Mn3+ spin to be parallel to the Te-Mn-Te bond, the ferromagnetic spin exchange between adjacent Mn3+ and Mn2+ ions, and the nearly equal numbers of Mn3+ and Mn2+ ions in each MnO2Te2 layer. We show that the spin orientation of the magnetic ions in an antiferromagnetically coupled perovskite layer, expected in the absence of nonmagnetic ion vacancies, cannot be altered by the magnetic ions of higher oxidation that result from trace vacancies at the nonmagnetic ion sites.}, number={21}, journal={INORGANIC CHEMISTRY}, author={Koo, Hyun-Joo and Whangbo, Myung-Hwan}, year={2019}, month={Nov}, pages={14769–14776} } @article{li_jin_wang_liu_wang_zheng_whangbo_kou_li_dai_et al._2019, title={Effect of the intra- and inter-triazine N-vacancies on the photocatalytic hydrogen evolution of graphitic carbon nitride}, volume={369}, ISBN={1873-3212}, DOI={10.1016/j.cej.2019.03.095}, abstractNote={We developed a new method to introduce N-vacancies of graphitic carbon nitride (GCN, typically in the Melon structure) at the inter-triazine sites and investigated how the visible-light photocatalytic H2 evolution of GCN is affected by the N-vacancies at the intra- and inter-triazine sites of GCN. Theoretical and experimental results show that these N-vacancies of GCN create singly-occupied defect states within the band gap acting as a trap for photogenerated electrons and act as the reaction sites for H+ reduction. Compared with the intra-triazine N-vacancy, the inter-triazine N-vacancy exhibits stronger electron localization leading to a more efficient H2 evolution. The photocatalytic reaction rate of GCN with inter-triazine N-vacancies is 9 times higher than that of “defect free” GCN, and 2.2 times higher normalized reaction rates than GCN with intra-triazine N-vacancies. The catalysis mechanism and the method to prepare melon with inter-triazine N-vacancies can be extended to explore new photocatalysts with high activities.}, journal={CHEMICAL ENGINEERING JOURNAL}, author={Li, Huiliang and Jin, Cui and Wang, Zeyan and Liu, Yuanyuan and Wang, Peng and Zheng, Zhaoke and Whangbo, Myung-Hwan and Kou, Liangzhi and Li, Yingjie and Dai, Ying and et al.}, year={2019}, pages={263–271} } @article{whangbo_xiang_koo_gordon_whitten_2019, title={Electronic and Structural Factors Controlling the Spin Orientations of Magnetic Ions}, volume={58}, ISSN={0020-1669 1520-510X}, url={http://dx.doi.org/10.1021/acs.inorgchem.9b00687}, DOI={10.1021/acs.inorgchem.9b00687}, abstractNote={Magnetic ions M in discrete molecules and extended solids form MLn complexes with their first-coordinate ligand atoms L. The spin moment of M in a complex MLn prefers a certain direction in coordinate space because of spin-orbit coupling (SOC). In this minireview, we examine the structural and electronic factors governing the preferred spin orientations. Elaborate experimental measurements and/or sophisticated computational efforts are required to find the preferred spin orientations of magnetic ions, largely because the energy scale of SOC is very small. The latter is also the very reason why one can readily predict the preferred spin orientation of M by analyzing the SOC-induced highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) interactions of the MLn complexes in terms of qualitative perturbation theory. The strength of this HOMO-LUMO interaction depends on the spin orientation, which is governed by the selection rules based on the minimum |ΔLz| value (i.e., the minimum difference in the magnetic quantum numbers) between the HOMO and LUMO. With the local z axis of MLn chosen as its n-fold rotational axis, the preferred spin orientation is parallel to the z axis (∥z) when |ΔLz| = 0 but perpendicular to the z axis (⊥z) when |ΔLz| = 1.}, number={18}, journal={Inorganic Chemistry}, publisher={American Chemical Society (ACS)}, author={Whangbo, Myung-Hwan and Xiang, Hongjun and Koo, Hyun-Joo and Gordon, Elijah E. and Whitten, Jerry L.}, year={2019}, month={Jun}, pages={11854–11874} } @article{gao_li_zhou_wang_zheng_wang_liu_dai_whangbo_huang_2019, title={Enhanced selectivity and activity for electrocatalytic reduction of CO2 to CO on an anodized Zn/carbon/Ag electrode}, volume={7}, ISSN={["2050-7496"]}, DOI={10.1039/c9ta04529e}, abstractNote={The selectivity and activity of the anodized Zn/C/Ag composite electrode containing a tiny amount of Ag (∼0.5 wt%) are enhanced by the synergistic effect of Zn, C and Ag.}, number={28}, journal={JOURNAL OF MATERIALS CHEMISTRY A}, author={Gao, Yugang and Li, Fengping and Zhou, Peng and Wang, Zeyan and Zheng, Zhaoke and Wang, Peng and Liu, Yuanyuan and Dai, Ying and Whangbo, Myung-Hwan and Huang, Baibiao}, year={2019}, month={Jul}, pages={16685–16689} } @article{an_liu_bian_wang_wang_zheng_dai_whangbo_huang_2019, title={Improving the photocatalytic hydrogen evolution of UiO-67 by incorporating Ce4+-coordinated bipyridinedicarboxylate ligands}, volume={64}, ISSN={["2095-9281"]}, DOI={10.1016/j.scib.2019.07.030}, abstractNote={UiO-67 is a Zr-based metal-organic framework (MOF) containing an organic linker namely, the dianion of biphenyl-4,4'-dicarboxylic acid (bpdc). Ce4+ metal ions (0.02 Ce to Zr atom ratio) were incorporated into UiO-67 via partially replacing bpdc with the dianion of 2,2'-bipyridine-5,5'-dicarboxylic acid (bpydc); thus, the latter forms a bpydc-Ce complex. The resulting product (i.e., UiO-67-Ce) demonstrated a photocatalytic hydrogen evolution rate that was over 10 times higher than that of UiO-67. Through this modification, a new energy transfer channel is opened up. The energy transfer between the bpdc and bpydc-Ce ligands (i.e., from excited bpdc to bpydc-Ce) weakened the recombination of the charge carriers, which was confirmed by photoluminescence, emission lifetime, and transient absorption measurements. This study presents a new way to construct highly efficient MOF photocatalysts.}, number={20}, journal={SCIENCE BULLETIN}, author={An, Yang and Liu, Yuanyuan and Bian, Hongtao and Wang, Zeyan and Wang, Peng and Zheng, Zhaoke and Dai, Ying and Whangbo, Myung-Hwan and Huang, Baibiao}, year={2019}, month={Oct}, pages={1502–1509} } @article{guan_wu_wang_zhang_wang_zheng_liu_dai_whangbo_huang_2019, title={Perovskite photocatalyst CsPbBr3-xIx with a bandgap funnel structure for H-2 evolution under visible light}, volume={245}, ISSN={["1873-3883"]}, DOI={10.1016/j.apcatb.2019.01.019}, abstractNote={A simple and efficient light-assisted method is employed to prepare powder samples of all-inorganic mixed-perovskite CsPbBr3-xIx from CsPbBr3 by ion exchange in aqueous HBr/KI solution such that the concentration of I in a sample particle decreases on going from the surface to the interior. CsPbBr3-xIx/Pt, namely, CsPbBr3-xIx samples loaded with Pt nanoparticles, shows a high performance for the hydrogen evolution under visible-light irradiation in aqueous HBr solution saturated with CsPbBr3. The H2 evolution rate of the CsPbBr3-xIx/Pt powders (200 mg) is determined to be 224 μmol h−1, under 120 mW cm-2 visible-light (λ ≥ 420 nm) illumination. The CsPbBr3-xIx samples have a high stability, with no apparent decrease in the catalytic activity after 50 h of repeated H2 evolution experiments. The apparent quantum efficiency of CsPbBr3-xIx/Pt is determined to be 2.15% under the irradiation of 450 nm light.}, journal={APPLIED CATALYSIS B-ENVIRONMENTAL}, author={Guan, Zihan and Wu, Yaqiang and Wang, Peng and Zhang, Qianqian and Wang, Zeyan and Zheng, Zhaoke and Liu, Yuanyuan and Dai, Ying and Whangbo, Myung-Hwan and Huang, Baibiao}, year={2019}, month={May}, pages={522–527} } @article{zhang_liu_wang_wang_zheng_qin_zhang_dai_whangbo_huang_2019, title={Selective photocatalytic conversion of alcohol to aldehydes by singlet oxygen over Bi-based metal-organic frameworks under UV-vis light irradiation}, volume={254}, ISSN={["1873-3883"]}, DOI={10.1016/j.apcatb.2019.05.024}, abstractNote={So far, most efforts in photocatalysis have been devoted to the separation of photogenerated electron-hole pairs, and possible use of excitons (i.e., electron-hole pairs) for photocatalytic processes has not received much attention. In this work, we studied the effect of metal dots on the excitonic behaviors of two bismuth-based MOFs, Bi-TATB and Bi-BTC (here the tridentate ligands TATB3− and BTC3− represent the carboxylates of 4,4′,4′'-s-triazine-2,4,6-triyl-tribenzoic and 1,3,5-benzenetricarboxylic acids, respectively). The organic ligands (TATB and BTC) display different emission properties from the corresponding Bi based MOFs. Specifically, TATB and BTC display strong fluorescence emission while Bi-TATB and Bi-BTC display strong phosphorescence emission, suggesting the higher efficiency of intersystem crossing for Bi-TATB and Bi-BTC. The reason is attributed to the coordination with Bi, which promotes the singlet→ triplet intersystem crossing of the organic ligand due to the heavy metal effect. The enhanced triplet excited emission of Bi-TATB and Bi-BTC was further confirmed by the detection of 1O2, as 1O2 is well known to be formed due to energy transfer from the triplet state of photosensitizers to the ground-state oxygen (3O2). With above understanding, Bi-TATB and Bi-BTC were finally used to high selective photooxidation of benzyl alcohol to benzaldehyde. This work presents new understanding of the photophysical properties of Bi based MOFs, which provides alternative ideas on designing materials for selective photo-oxidation.}, journal={APPLIED CATALYSIS B-ENVIRONMENTAL}, author={Zhang, Ruoqian and Liu, Yuanyuan and Wang, Zeyan and Wang, Peng and Zheng, Zhaoke and Qin, Xiaoyan and Zhang, Xiaoyang and Dai, Ying and Whangbo, Myung-Hwan and Huang, Baibiao}, year={2019}, month={Oct}, pages={463–470} } @article{an_liu_wang_wang_zheng_dai_qin_zhang_whangbo_huang_2019, title={Stabilizing the titanium-based metal organic frameworks in water by metal cations with empty or partially-filled d orbitals}, volume={533}, ISSN={["1095-7103"]}, DOI={10.1016/j.jcis.2018.08.049}, abstractNote={Though titanium-based metal-organic frameworks (MOFs) are declared to be relatively water stable, their framework gradually collapses in water within days due to the attack of OH− to OTiO bond. For practical applications of titanium-based MOFs, it is crucial to solve their instability problem in water. We searched for a simple and efficient method to enhance the stability of titanium-based MOFs in water by using Ti-ATA (ATA = 2-aminoterephthallate ion) as a representative titanium-based MOF. Here, we show that the stability of Ti-ATA in water is greatly improved nearly without affecting its porosity and photocatalytic activity by treating it with aqueous solutions containing metal ions of empty d orbitals (Y3+, La3+, Ce3+, Nd3+ and Tm3+) or partially-filled d orbitals (Cr3+).}, journal={JOURNAL OF COLLOID AND INTERFACE SCIENCE}, author={An, Yang and Liu, Yuanyuan and Wang, Zeyan and Wang, Peng and Zheng, Zhaoke and Dai, Ying and Qin, Xiaoyan and Zhang, Xiaoyang and Whangbo, Myung-Hwan and Huang, Baibiao}, year={2019}, month={Jan}, pages={9–12} } @article{uma_vasilchikova_sobolev_raganyan_sethi_koo_whangbo_presniakov_glazkova_vasiliev_et al._2019, title={Synthesis and Characterization of Sodium-Iron Antimonate Na2FeSbO5: One-Dimensional Antiferromagnetic Chain Compound with a Spin-Glass Ground State}, volume={58}, ISSN={["1520-510X"]}, DOI={10.1021/acs.inorgchem.9b00212}, abstractNote={A new oxide, sodium–iron antimonate, Na2FeSbO5, was synthesized and structurally characterized, and its static and dynamic magnetic properties were comprehensively studied both experimentally by dc and ac magnetic susceptibility, magnetization, specific heat, electron spin resonance (ESR) and Mössbauer measurements, and theoretically by density functional calculations. The resulting single-crystal structure (a = 15.6991(9) Å; b = 5.3323 (4) Å; c = 10.8875(6) Å; S.G. Pbna) consists of edge-shared SbO6 octahedral chains, which alternate with vertex-linked, magnetically active FeO4 tetrahedral chains. The 57Fe Mössbauer spectra confirmed the presence of high-spin Fe3+ (3d5) ions in a distorted tetrahedral oxygen coordination. The magnetic susceptibility and specific heat data show the absence of a long-range magnetic ordering in Na2FeSbO5 down to 2 K, but ac magnetic susceptibility unambigously demonstrates spin-glass-type behavior with a unique two-step freezing at Tf1 ≈ 80 K and Tf2 ≈ 35 K. Magnetic hyperfine splitting of 57Fe Mössbauer spectra was observed below T* ≈ 104 K (Tf1 < T*). The spectra just below T* (Tf1 < T < T*) exhibit a relaxation behavior caused by critical spin fluctuations, indicating the existence of short-range correlations. The stochastic model of ionic spin relaxation was used to account for the shape of the Mössbauer spectra below the freezing temperature. A complex slow dynamics is further supported by ESR data revealing two different absorption modes presumably related to ordered and disordered segments of spin chains. The data imply a spin-cluster ground state for Na2FeSbO5.}, number={17}, journal={INORGANIC CHEMISTRY}, author={Uma, Sitharaman and Vasilchikova, Tatyana and Sobolev, Alexey and Raganyan, Grigory and Sethi, Aanchal and Koo, Hyun-Joo and Whangbo, Myun-Hwan and Presniakov, Igor and Glazkova, Iana and Vasiliev, Alexander and et al.}, year={2019}, month={Sep}, pages={11333–11350} } @article{koo_kasapbasi_whitten_whangbo_2019, title={The Conceptual Dilemma of the One-Electron Picture in Describing the Uniaxial Magnetism at Linear Coordination Sites}, volume={2019}, ISSN={1434-1948}, url={http://dx.doi.org/10.1002/ejic.201900370}, DOI={10.1002/ejic.201900370}, abstractNote={High‐spin Fe 2+ , Fe + and Co 2+ ions at linear two‐coordination sites exhibit uniaxial magnetism. In the one‐electron picture, the uniaxial magnetism of the Fe 2+ ion is explained, while those of the Fe + and Co 2+ ions are not, if the d‐state split pattern is 1e < 2e < 1a. The opposite is true if the d‐state split pattern is 1a < 1e < 2e. We resolved this conceptual dilemma by evaluating the relative stabilities for the various L states of linear molecules (Fe L 2 ) 0 , (Fe L 2 ) – , and (Co L 2 ) 0 with L = C(SiH 3 ) 3 on the basis of first‐principles broken‐symmetry and configuration interaction calculations. In the first‐principles picture, the total energy of an electron configuration depends not only on the energy sequence of the occupied d‐states, as do the one‐electron picture, but also on the electron repulsion between occupied d‐states, which is neglected by the one‐electron picture.}, number={21}, journal={European Journal of Inorganic Chemistry}, publisher={Wiley}, author={Koo, Hyun-Joo and Kasapbasi, Esra E. and Whitten, Jerry L. and Whangbo, Myung-Hwan}, year={2019}, month={May}, pages={2630–2634} } @article{chi_xu_xue_zhang_chen_whangbo_guo_deng_2019, title={Triple-Kagome-Layer Slabs of Mixed-Valence Rare-Earth Ions Exhibiting Quantum Spin Liquid Behaviors: Synthesis and Characterization of Eu9MgS2B20O41}, volume={141}, ISSN={["0002-7863"]}, DOI={10.1021/jacs.9b04627}, abstractNote={We prepared a new rare-earth compound, Eu9MgS2B20O41 (EMSBO), and characterized its structural and physical properties. EMSBO consists of triple-Kagomé-layer slabs separated by nonmagnetic ions and groups. Within each slab, intervalence charge transfer has been found to occur between the Eu2+ and Eu3+ Kagomé layers, a new channel for quantum fluctuation of magnetic moments. The measured magnetic susceptibilities and the specific heat capacity exhibit very similar features characteristic of quantum spin liquid behaviors observed in other materials.}, number={24}, journal={JOURNAL OF THE AMERICAN CHEMICAL SOCIETY}, author={Chi, Yang and Xu, Jing and Xue, Huai-Guo and Zhang, Yueping and Chen, Xiaolong and Whangbo, Myung-Hwan and Guo, Sheng-Ping and Deng, Shuiquan}, year={2019}, month={Jun}, pages={9533–9536} } @article{liang_wang_li_zhang_wang_dai_zhang_liu_whangbo_huang_2018, title={Adsorption of gaseous ethylene via induced polarization on plasmonic photocatalyst Ag/AgCl/TiO2 and subsequent photodegradation}, volume={220}, ISSN={["1873-3883"]}, DOI={10.1016/j.apcatb.2017.07.075}, abstractNote={The removal of nonpolar gaseous ethylene molecules on the plasmonic photocatalyst Ag/AgCl/TiO2 was examined under simulated sunlight irradiation, to find that it has a markedly high activity for the oxidation of ethylene molecules. Systematic experiments, carried out to probe the cause for this observation, indicate that the strong electric field mainly on the Ag nanoparticles (NPs) generated by their surface plasmon resonance (SPR) induces polarization in gaseous ethylene molecules hence enhancing their adsorption on the catalysts and their subsequent photodegradation, and that TiO2 acts as a substrate for dispersing Ag/AgCl nanoparticles to have a larger active surface area. This study provides new ideas towards designing advanced photocatalysts for the degradation of nonpolar gaseous molecules.}, journal={APPLIED CATALYSIS B-ENVIRONMENTAL}, author={Liang, Xizhuang and Wang, Peng and Li, Mengmeng and Zhang, Qianqian and Wang, Zeyan and Dai, Ying and Zhang, Xiaoyang and Liu, Yuanyuan and Whangbo, Myung-Hwan and Huang, Baibiao}, year={2018}, month={Jan}, pages={356–361} } @article{zhu_wang_wang_liu_zheng_zhang_zhang_dai_whangbo_huang_2018, title={Co3O4 nanobelt arrays assembled with ultrathin nanosheets as highly efficient and stable electrocatalysts for the chlorine evolution reaction}, volume={6}, ISSN={["2050-7496"]}, DOI={10.1039/c8ta03689f}, abstractNote={We report Co3O4 nanobelt arrays (NBAs) assembled with ultrathin nanosheets prepared on fluorine doped tin oxide (FTO) substrates as electrocatalysts for the CER.}, number={26}, journal={JOURNAL OF MATERIALS CHEMISTRY A}, author={Zhu, Xianglin and Wang, Peng and Wang, Zeyan and Liu, Yuanyuan and Zheng, Zhaoke and Zhang, Qianqian and Zhang, Xiaoyang and Dai, Ying and Whangbo, Myung-Hwan and Huang, Baibiao}, year={2018}, month={Jul}, pages={12718–12723} } @article{lee_kim_tak_cho_shim_lim_whangbo_2018, title={Comparison of the electronic and thermoelectric properties of three layered phases Bi2Te3, PbBi2Te4 and PbBi4Te7: LEGO thermoelectrics}, volume={8}, ISSN={["2158-3226"]}, DOI={10.1063/1.5047823}, abstractNote={The electronic and thermoelectric properties of Bi2Te3, PbBi2Te4 and PbBi4Te7 were examined on the basis of density functional theory (DFT) calculations and thermoelectric transport property measurements. The layered phase PbBi4Te7 is composed of the slabs forming the layered phases Bi2Te3 and PbBi2Te4. The electronic structure of PbBi4Te7 around the valence band maximum and conduction band minimum exhibits those of Bi2Te3 and PbBi2Te4. The band gap of PbBi4Te7 lies in between those of Bi2Te3 and PbBi2Te4, and the density of states of PbBi4Te7 is well approximated by the sum of those of Bi2Te3 and PbBi2Te4. In terms of the carrier concentration, the carrier mobility, the carrier lifetime, the electrical conductivity normalized to the carrier lifetime, and the effective mass, the layered phases Bi2Te3, PbBi4Te7 and PbBi2Te4 form a group of thermoelectrics, which have the structures composed of several different slabs and whose thermoelectric properties are approximated by the average of those of the constituent slabs. We propose to use the term “LEGO thermoelectrics” to describe such a family of thermoelectric materials that operate in a desired temperature range and possess predictable thermoelectric properties.}, number={11}, journal={AIP ADVANCES}, author={Lee, Changhoon and Kim, Jae Nyeong and Tak, Jang-Yeul and Cho, Hyung Koun and Shim, Ji Hoon and Lim, Young Soo and Whangbo, Myung-Hwan}, year={2018}, month={Nov} } @article{wu_wang_zhu_zhang_wang_liu_zou_dai_whangbo_huang_2018, title={Composite of CH3NH3PbI3 with reduced graphene oxide as a highly efficient and stable visible-light photocatalyst for hydrogen evolution in aqueous HI solution}, volume={30}, number={7}, journal={Advanced Materials}, author={Wu, Y. Q. and Wang, P. and Zhu, X. L. and Zhang, Q. Q. and Wang, Z. Y. and Liu, Y. Y. and Zou, G. Z. and Dai, Y. and Whangbo, M. H. and Huang, B. B.}, year={2018} } @article{lou_zhu_yang_zhang_whangbo_li_huang_2018, title={Continual injection of photoinduced electrons stabilizing surface plasmon resonance of non-elemental-metal plasmonic photocatalyst CdS/WO3-x for efficient hydrogen generation}, volume={226}, ISSN={["1873-3883"]}, DOI={10.1016/j.apcatb.2017.12.023}, abstractNote={To remedy the instability problem of the non-elemental-metal (NEM) plasmonic photocatalyst WO3−x in aqueous solution, a novel strategy of photoinduced electron injection was applied to construct CdS/WO3−x hetereostructures by growing WO3−x on semiconductor CdS nanowires. Under visible/near-infrared light irradiation, the NEM plasmonic CdS/WO3−x nanowires are highly stable and exhibit a much higher activity (1.60 mmol g−1 h−1) than do plasmonic WO3−x (negligible amount) and semiconductor CdS (0.53 mmol g−1 h−1) in hydrogen generation. Wavelength dependent photocatalytic performance and Single-particle PL study demonstrate that photo-excited electrons on CdS continually inject into conduction band of WO3−x, so that the surface plasmon resonance (SPR) of the NEM plasmonic photocatalyst WO3−x is sustained while hot electrons generated by the SPR excitation are consumed for hydrogen generation.}, journal={APPLIED CATALYSIS B-ENVIRONMENTAL}, author={Lou, Zaizhu and Zhu, Mingshan and Yang, Xianguang and Zhang, Yao and Whangbo, Myung-Hwan and Li, Baojun and Huang, Baibiao}, year={2018}, month={Jun}, pages={10–15} } @article{li_zhang_wang_wang_liu_zhang_qin_dai_whangbo_huang_2018, title={Endotaxial growth of [100]-oriented TaON films on LiTaO3 single crystals for enhanced photoelectrochemical water splitting}, volume={2}, number={6}, journal={Solar RRL}, author={Li, H. L. and Zhang, B. and Wang, Z. Y. and Wang, P. and Liu, Y. Y. and Zhang, X. Y. and Qin, X. Y. and Dai, Y. and Whangbo, M. H. and Huang, B. B.}, year={2018} } @article{wu_wang_guan_liu_wang_zheng_jin_dai_whangbo_huang_2018, title={Enhancing the Photocatalytic Hydrogen Evolution Activity of Mixed-Halide Perovskite CH3NH3PbBr3-xIx Achieved by Bandgap Funneling of Charge Carriers}, volume={8}, ISSN={["2155-5435"]}, DOI={10.1021/acscatal.8b02374}, abstractNote={Powder samples of mixed halide perovskite MAPbBr3–xIx (MA = methylammonium ion, CH3NH3+) were prepared by employing a facile light-assisted halide-exchange method in aqueous halide solution at room temperature. It is found that the distribution of iodide ions in the MAPbBr3–xIx particles tends to be largest on the surface and becomes lower on going into the interior so that they have a correct bandgap funnel structure that is needed for transferring photogenerated charge carriers from the interior to the surface. Consequently, the MAPbBr3–xIx/Pt powder sample (250 mg) exhibits an enhanced photocatalytic activity for a H2 evolution under visible light (100 mW cm–2, λ ≥ 420 nm) with the rate of 651.2 μmol h–1 and a solar-to-chemical conversion efficiency of 1.05%.}, number={11}, journal={ACS CATALYSIS}, author={Wu, Yaqiang and Wang, Peng and Guan, Zihan and Liu, Junxue and Wang, Zeyan and Zheng, Zhaoke and Jin, Shengye and Dai, Ying and Whangbo, Myung-Hwan and Huang, Baibiao}, year={2018}, month={Nov}, pages={10349–10357} } @article{lomnytska_dzevenko_babizhetskyy_toma_smolyak_gordon_whangbo_koehler_2018, title={Interaction of tantalum, titanium and phosphorus at 1070 K: Phase diagram and structural chemistry}, volume={732}, ISSN={["1873-4669"]}, DOI={10.1016/j.jallcom.2017.10.247}, abstractNote={The solid state phase diagram for the equilibria of the ternary Ta-Ti-P system was established by X-ray powder diffraction at T = 1070 K in the region up to 67 at.% P. Isostructural compounds Ta3P and Ti3P (both Ti3P-type) form a continuous series of substitution-type solid solutions. The majority of binary compounds form substitution-type solid solutions, in which the substitution of Ti for Ta, or Ta for Ti, takes place. The crystal structure investigation of the new ternary phosphide demonstrates that this phase is isotypical to the OsGe2 structure type and has a small homogeneity range, which can be described by the formula Та1-xТіxР2 (x = 0.07(3)−0.145(7), space group C2/m, a = 8.8556(9)−8.8446(2), b = 3.2654(4)−3.2605(1), c = 7.4846(8)−7.4741(1) Å, β = 119.307(2)−119.308(1)°). Our density functional theory (DFT) electronic structure calculations show that the stoichiometric composition TaP2 has no electronic instability, although it does not exist under the thermal conditions used in present study. The addition of a small amount of Ti leads to a ternary phase Та1-xТіxР2 (x = 0.07(3)−0.145(7)) with a higher thermal stability compared to TaP2.}, journal={JOURNAL OF ALLOYS AND COMPOUNDS}, author={Lomnytska, Ya. and Dzevenko, M. and Babizhetskyy, V. and Toma, O. and Smolyak, O. and Gordon, E. E. and Whangbo, M. -H. and Koehler, J.}, year={2018}, month={Jan}, pages={777–783} } @article{whangbo_deng_koehler_simon_2018, title={Interband Electron Pairing for Superconductivity from the Breakdown of the Born-Oppenheimer Approximation}, volume={19}, ISSN={["1439-7641"]}, DOI={10.1002/cphc.201800738}, abstractNote={The origin of interband electron pairing responsible for enhancing superconductivity and the factors controlling its strength were examined. We show that the interband electron pairing is a natural consequence of breaking down the Born-Oppenheimer approximation during the electron-phonon interactions. Its strength is determined by the pair-state excitations around the Fermi surfaces that take place to form a superconducting state. Fermi surfaces favorable for the pairing were found and its implications were discussed.}, number={23}, journal={CHEMPHYSCHEM}, author={Whangbo, Myung-Hwan and Deng, Shuiquan and Koehler, Juergen and Simon, Arndt}, year={2018}, month={Dec}, pages={3191–3195} } @article{golubev_bruecher_schulz_kremer_schmidt_gordon_whangbo_2018, title={Low-Dimensional Magnetic Properties of Natural and Synthetic Mixite (Bi,Ca)Cu-6(OH)(6)(AsO4)(3)center dot nH(2)O (n approximate to 3) and Goudeyite YCu6(OH)(6)(AsO4)(3)center dot nH(2)O (n approximate to 3)}, volume={644}, ISSN={["1521-3749"]}, DOI={10.1002/zaac.201800344}, abstractNote={The structural, vibrational, and especially the magnetic properties of natural and synthetic polycrystalline samples of the minerals mixite with composition (Bi,Ca)Cu 6 (OH) 6 (AsO 4 ) 3 · n H 2 O ( n ≈ 3) and goudeyite with composition YCu 6 (OH) 6 (AsO 4 ) 3 · n H 2 O ( n ≈ 3) were investigated. The magnetic susceptibilities are characterized by low‐dimensional antiferromagnetic short range ordering and can be well fitted by the theoretical susceptibilities of a spin S = 1/2 alternating Heisenberg chain with nearest‐neighbor spin exchange ranging between 200 K and 130 K for natural mixite and synthetic goudeyite, respectively. The alternation parameters, i.e. the ratios of nearest and next‐nearest neighbor spin exchange range between 0.52 for natural mixite and 0.75 for synthetic mixite and goudeyite, respectively. The experimentally observed spin exchange parameters are consistent with DFT calculations of the spin exchange parameters.}, number={24}, journal={ZEITSCHRIFT FUR ANORGANISCHE UND ALLGEMEINE CHEMIE}, author={Golubev, Aleksandr and Bruecher, Eva and Schulz, Armin and Kremer, Reinhard K. and Schmidt, Franz X. and Gordon, Elija E. and Whangbo, Myung-Hwan}, year={2018}, month={Dec}, pages={1782–1790} } @article{leiner_oh_kolesnikov_stone_le_kenny_powell_mourigal_gordon_whangbo_et al._2018, title={Magnetic excitations of the Cu2+ quantum spin chain in Sr3CuPtO6}, volume={97}, ISSN={["2469-9969"]}, DOI={10.1103/physrevb.97.104426}, abstractNote={We report the magnetic excitation spectrum as measured by inelastic neutron scattering for a polycrystalline sample of ${\mathrm{Sr}}_{3}{\mathrm{CuPtO}}_{6}$. Modeling the data by the 2+4 spinon contributions to the dynamical susceptibility within the chains, and with interchain coupling treated in the random phase approximation, accounts for the major features of the powder-averaged structure factor. The magnetic excitations broaden considerably as temperature is raised, persisting up to above 100 K and displaying a broad transition as previously seen in the susceptibility data. No spin gap is observed in the dispersive spin excitations at low momentum transfer, which is consistent with the gapless spinon continuum expected from the coordinate Bethe ansatz. However, the temperature dependence of the excitation spectrum gives evidence of some very weak interchain coupling.}, number={10}, journal={PHYSICAL REVIEW B}, author={Leiner, J. C. and Oh, Joosung and Kolesnikov, A. I. and Stone, M. B. and Le, Manh Duc and Kenny, E. P. and Powell, B. J. and Mourigal, M. and Gordon, E. E. and Whangbo, M. -H. and et al.}, year={2018}, month={Mar} } @article{gordon_cheng_kim_cheong_deng_whangbo_2018, title={Nonequivalent Spin Exchanges of the Hexagonal Spin Lattice Affecting the Low-Temperature Magnetic Properties of RInO3 (R = Gd, Tb, Dy): Importance of Spin-Orbit Coupling for Spin Exchanges between Rare-Earth Cations with Nonzero Orbital Moments}, volume={57}, ISSN={["1520-510X"]}, DOI={10.1021/acs.inorgchem.8b01274}, abstractNote={Rare-earth indium oxides RInO3 (R = Gd, Tb, Dy) consist of spin-frustrated hexagonal spin lattices made up of rare-earth ions R3+, where R3+ = Gd3+ (f7, L = 0), Tb3+ (f8, L = 3), and Dy3+ (f9, L = 5). We carried out DFT calculations for RInO3, including on-site repulsion U with/without spin-orbit coupling (SOC), to explore if their low-temperature magnetic properties are related to the two nonequivalent nearest-neighbor (NN) spin exchanges of their hexagonal spin lattices. Our DFT + U + SOC calculations predict that the orbital moments of the Tb3+ and Dy3+ ions are smaller than their free-ion values by ∼2μB while the Tb3+ spins have an in-plane magnetic anisotropy, in agreement with the experiments. This suggests that the f orbitals of each R3+ (R = Tb, Dy) ion are engaged, though weakly, in bonding with the surrounding ligand atoms. The magnetic properties of GdInO3 with the zero orbital moment are adequately described by the spin exchanges extracted by DFT + U calculations. In describing the magnetic properties of TbInO3 and DyInO3 with nonzero orbital moments, however, the spin exchanges extracted by DFT + U + SOC calculations are necessary. The spin exchanges of RInO3 (R = Gd, Tb, Dy) are dominated by the two NN spin exchanges J1 and J2 of their hexagonal spin lattice, in which the honeycomb lattice of J2 forms spin-frustrated ( J1, J1, J2) triangles. The J2/ J1 ratios are calculated to be ∼3, ∼1.7, and ∼1 for GdInO3, TbInO3, and DyInO3, respectively. This suggests that the antiferromagnetic (AFM) ordering of GdInO3 below 1.8 K is most likely an AFM ordering of its honeycomb spin lattice and that TbInO3 would exhibit low-temperature magnetic properties similar to those of GdInO3 while DyInO3 would not.}, number={15}, journal={INORGANIC CHEMISTRY}, author={Gordon, Elijah E. and Cheng, Xiyue and Kim, Jaewook and Cheong, Sang-Wook and Deng, Shuiquan and Whangbo, Myung-Hwan}, year={2018}, month={Aug}, pages={9260–9265} } @article{gordon_derakhshan_thompson_whangho_2018, title={Spin-Density Wave as a Superposition of Two Magnetic States of Opposite Chirality and Its Implications}, volume={57}, ISSN={["1520-510X"]}, DOI={10.1021/acs.inorgchem.8b01494}, abstractNote={A magnetic solid with weak spin frustration tends to adopt a noncollinear magnetic structure such as a cycloidal structure below a certain temperature and a spin-density wave (SDW) slightly above this temperature. The causes for these observations were explored by studying the magnetic structure of BaYFeO4, which undergoes a SDW and a cycloidal phase transition below 48 and 36 K, respectively, in terms of the density functional theory calculations. We show that a SDW structure arises from a superposition of two magnetic states of opposite chirality, an SDW state precedes a chiral magnetic state because of the lattice relaxation, and whether a SDW is transversal or longitudinal is governed by the magnetic anisotropy of magnetic ions.}, number={16}, journal={INORGANIC CHEMISTRY}, author={Gordon, Elijah E. and Derakhshan, Shahab and Thompson, Corey M. and Whangho, Myung-Hwan}, year={2018}, month={Aug}, pages={9782–9785} } @article{cheng_whangbo_guo_hong_deng_2018, title={The Large Second-Harmonic Generation of LiCs2PO4 is caused by the Metal-Cation-Centered Groups}, volume={57}, ISSN={["1521-3773"]}, DOI={10.1002/anie.201711465}, abstractNote={We evaluated the individual atom contributions to the second harmonic generation (SHG) coefficients of LiCs2PO4 (LCPO) by introducing the partial response functionals on the basis of first principles calculations. The SHG response of LCPO is dominated by the metal-cation-centered groups CsO6 and LiO4, not by the nonmetal-cation-centered groups PO4 one expects from the existing models and theories. The SHG coefficients of LCPO are determined mainly by the occupied orbitals O-2p and Cs-5p as well as by the unoccupied orbitals Cs-5d and Li-2p. For the SHG response of a material, the polarizable atomic orbitals of the occupied and the unoccupied states are both important.}, number={15}, journal={ANGEWANDTE CHEMIE-INTERNATIONAL EDITION}, author={Cheng, Xiyue and Whangbo, Myung-Hwan and Guo, Guo-Cong and Hong, Maochun and Deng, Shuiquan}, year={2018}, month={Apr}, pages={3933–3937} } @article{lu_mentre_gordon_whangbo_wattiaux_duttine_tiercelin_kabbour_2017, title={A comprehensive study of magnetic exchanges in the layered oxychalcogenides Sr(3)Fe(2)O(5)Cu(2)Q(2) (Q = S, Se)}, volume={444}, ISSN={["1873-4766"]}, DOI={10.1016/j.jmmm.2017.07.026}, abstractNote={The layered oxysulfide Sr3Fe2O5Cu2S2 was prepared, and its crystal structure and magnetic properties were characterized by synchrotron X-ray diffraction (XRD), powder neutron diffraction (PND), Mössbauer spectroscopy measurements and by density functional theory (DFT) calculations. In addition, the spin exchange interactions leading to the ordered magnetic structure of Sr3Fe2O5Cu2S2 were compared with those of its selenium analogue Sr3Fe2O5Cu2Se2. The oxysulfide Sr3Fe2O5Cu2S2 adopts a G-type antiferromagnetic (AFM) structure at a temperature in the range 485–512 K, which is comparable with the three-dimensional (3D) AFM ordering temperature, TN ≈ 490 K, found for Sr3Fe2O5Cu2Se2. Consistent with this observation, the spin exchange interactions of the magnetic (Sr3Fe2O5)2+ layers are slightly greater (but comparable) for oxysulfide than for the oxyselenide. Attempts to reduce or oxidize Sr3Fe2O5Cu2S2 using topochemical routes yield metallic Fe.}, journal={JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS}, author={Lu, Minfeng and Mentre, Olivier and Gordon, Elijah E. and Whangbo, Myung-Hwan and Wattiaux, Alain and Duttine, Mathieu and Tiercelin, Nicolas and Kabbour, Houria}, year={2017}, month={Dec}, pages={147–153} } @article{xu_an_liu_qin_zhang_dai_wang_wang_whangbo_huang_2017, title={Enhancing the photocatalytic activity of BiOX (X = Cl, Br, and I), (BiO)(2)CO3 and Bi2O3 by modifying their surfaces with polar organic anions, 4-substituted thiophenolates}, volume={5}, ISSN={["2050-7496"]}, DOI={10.1039/c7ta03970k}, abstractNote={Bi-based semiconductors surface-modified by polar organic molecules display extended visible light absorption and enhanced photocatalytic activity.}, number={27}, journal={JOURNAL OF MATERIALS CHEMISTRY A}, author={Xu, Benyan and An, Yang and Liu, Yuanyuan and Qin, Xiaoyan and Zhang, Xiaoyang and Dai, Ying and Wang, Zeyan and Wang, Peng and Whangbo, Myung-Hwan and Huang, Baibiao}, year={2017}, month={Jul}, pages={14406–14414} } @article{barroux_jiang_paul_massuyeau_geois_gordon_whangbo_jobic_gautier_2017, title={Fine-Tuning the Properties of Doped Multifunctional Materials by Controlled Reduction of Dopants}, volume={23}, ISSN={["1521-3765"]}, DOI={10.1002/chem.201605707}, abstractNote={The physical properties of doped multifunctional compounds are commonly tuned by controlling the amount of dopants, but this control is limited because all the properties are influenced simultaneously by this single parameter. Here, we present a strategy that enables the fine-tuning of a specific combination of properties by controlling the reduction of dopants. The feasibility of this approach was demonstrated by optimizing the near-IR photoluminescence of strontium titanate SrTiO3 :Ni for potential applications in biomedicine for a range of absorbance in the visible/near-IR region. We discussed how material properties, such as luminescence, conductivity, or photocatalytic properties can be designed by carefully controlling the ratio of dopants in different oxidation states.}, number={13}, journal={CHEMISTRY-A EUROPEAN JOURNAL}, author={Barroux, Hugo and Jiang, Tengfei and Paul, Camille and Massuyeau, Florian and Geois, Romain and Gordon, Elijah E. and Whangbo, Myung-Hwan and Jobic, Stephane and Gautier, Romain}, year={2017}, month={Mar}, pages={2998–3001} } @article{gordon_koo_deng_koehler_whangbo_2017, title={Group of Quantum Bits Acting as a Bit Using a Single-Domain Ferromagnet of Uniaxial Magnetic Ions}, volume={18}, ISSN={["1439-7641"]}, DOI={10.1002/cphc.201700609}, abstractNote={Read/write operations with individual quantum bits (i.e., qbits) are a challenging problem to solve in quantum computing. To alleviate this difficulty, we considered the possibility of using a group of qbits that act collectively as a bit (hereafter, a group bit or a gbit, in short). A promising candidate for a gbit is a single-domain ferromagnet (SDF) independent of its size, which can be prepared as a magnet of well-separated uniaxial magnetic ions (UMIs) at sites of no electric dipole moment with their uniaxial axes aligned along one common direction. When magnetized, the UMIs of such a magnet have a ferromagnetic (FM) arrangement and the resulting SDF becomes a gbit with its two opposite moment orientations representing the |0⟩ and |1⟩ states of a bit. We probed the requirements for such magnets and identified several 2H-perovskites as materials satisfying these requirements.}, number={16}, journal={CHEMPHYSCHEM}, author={Gordon, Elijah E. and Koo, Hyun-Joo and Deng, Shuiquan and Koehler, Juergen and Whangbo, Myung-Hwan}, year={2017}, month={Aug}, pages={2147–2150} } @article{clune_hughey_lee_abhyankar_ding_dalal_whangbo_singleton_musfeldt_2017, title={Magnetic field-temperature phase diagram of multiferroic [(CH3)(2)NH2]Mn(HCOO)(3)}, volume={96}, ISSN={["2469-9969"]}, DOI={10.1103/physrevb.96.104424}, abstractNote={We combined pulsed field magnetization and first-principles spin-density calculations to reveal the magnetic field-temperature phase diagram and spin state character in multiferroic $[{({\mathrm{CH}}_{3})}_{2}{\mathrm{NH}}_{2}]\mathrm{Mn}{(\mathrm{HCOO})}_{3}$. Despite similarities with the rare earth manganites, the phase diagram is analogous to other Mn-based quantum magnets with a 0.31 T spin flop, a 15.3 T transition to the fully polarized state, and short-range correlations that persist above the ordering temperature. The experimentally accessible saturation field opens the door to exploration of the high-field phase.}, number={10}, journal={PHYSICAL REVIEW B}, author={Clune, A. J. and Hughey, K. D. and Lee, C. and Abhyankar, N. and Ding, X. and Dalal, N. S. and Whangbo, M. -H. and Singleton, J. and Musfeldt, J. L.}, year={2017}, month={Sep} } @article{al-wahish_o'neal_lee_fan_hughey_yokosuk_clune_li_schlueter_manson_et al._2017, title={Magnetic phase transitions and magnetoelastic coupling in S=1/2 Heisenberg antiferromagnets}, volume={95}, ISSN={["2469-9969"]}, DOI={10.1103/physrevb.95.104437}, abstractNote={We combined magneto-infrared spectroscopy and first-principles calculations to unravel the role of spin-phonon coupling in the vicinity of the magnetic field-driven phase transitions in two chemically similar $S=1/2$ Heisenberg antiferromagnets, ${\mathrm{CuF}}_{2}({\mathrm{H}}_{2}\mathrm{O}){}_{2}$(3-Clpy) and $[\mathrm{Cu}{(\mathrm{pyz})}_{2}({\mathrm{HF}}_{2})]{\mathrm{PF}}_{6}$. This comparison resolves questions about the conditions under which the lattice participates in magnetic-field-driven transitions and, at the same time, provides a way to predict how the lattice is likely to support microscopic spin rearrangements.}, number={10}, journal={PHYSICAL REVIEW B}, author={al-Wahish, Amal and O'Neal, K. R. and Lee, C. and Fan, S. and Hughey, K. and Yokosuk, M. O. and Clune, A. J. and Li, Z. and Schlueter, J. A. and Manson, J. L. and et al.}, year={2017}, month={Mar} } @article{bussmann-holder_koehler_simon_whangbo_bianconi_2017, title={Multigap Superconductivity at Extremely High Temperature: A Model for the Case of Pressurized H2S}, volume={30}, ISSN={["1557-1947"]}, DOI={10.1007/s10948-016-3947-7}, abstractNote={It is known that in pressurized H2S, the complex electronic structure in the energy range of 200 meV near the chemical potential can be separated into two electronic components: the first characterized by steep bands with a high Fermi velocity and the second by flat bands with a vanishing Fermi velocity. Also, the phonon modes interacting with electrons at the Fermi energy can be separated into two components: hard modes with high energy around 150 meV and soft modes with energies around 60 meV. Therefore, we discuss here a multiband scenario in the standard Bardeen–Cooper–Schrieffer (BCS) approximation where the effective BCS coupling coefficient is in the range 0.1–0.32. We consider a first (second) BCS condensate in the strong (weak) coupling regime 0.32 (0.15). We discuss different scenarios segregated in different portions of the material. The results show the phenomenology of unconventional superconducting phases in this two-gap superconductivity scenario where there are two electronic components in two Fermi surface spots, and the pairing is mediated by either a soft or a hard phonon branch where the interband exchange term, also if small, plays a key role for the emergence of high-temperature superconductivity in pressurized sulfur hydride.}, number={1}, journal={JOURNAL OF SUPERCONDUCTIVITY AND NOVEL MAGNETISM}, author={Bussmann-Holder, A. and Koehler, J. and Simon, A. and Whangbo, M. and Bianconi, A.}, year={2017}, month={Jan}, pages={151–156} } @article{behrh_isobe_massuyeau_serier-brault_gordon_koo_whangbo_gautier_jobic_2017, title={Oxygen-Vacancy-Induced Midgap States Responsible for the Fluorescence and the Long-Lasting Phosphorescence of the Inverse Spinel Mg(Mg,Sn)O-4}, volume={29}, ISSN={["1520-5002"]}, DOI={10.1021/acs.chemmater.6b03906}, abstractNote={Samples of inverse spinel Mg2SnO4 were prepared using a ceramic method, their phosphorescence phenomenon was probed by optical measurements, and its cause was explored on the basis of density functional theory calculations for model structures of Mg2SnO4 with oxygen vacancies VO. Mg2SnO4 exhibits long-lasting luminescence at two different wavelength regions, peaking at ∼498 and ∼755 nm. A Sn-VO-Sn defect plus a Mg vacancy VMg away from the VO generates the empty midgap states, σSn-Sn and σSn-Sn*, localized at the Sn-VO-Sn defect, while an oxygen vacancy VO between adjacent Sn4+ and Mg2+ sites creates a filled midgap state Sn2+ (5s2 lone pair) lying below the σSn-Sn level. The long-lasting luminescence at two different wavelength regions and the up-conversion photostimulated luminescence observed for undoped Mg2SnO4 are well explained by considering the σSn-Sn* level as the trapping level for a photogenerated electron.}, number={3}, journal={CHEMISTRY OF MATERIALS}, author={Behrh, Gaganpreet Kaur and Isobe, Masahiko and Massuyeau, Florian and Serier-Brault, Helene and Gordon, Elijah E. and Koo, Hyun-Joo and Whangbo, Myung-Hwan and Gautier, Romain and Jobic, Stephane}, year={2017}, month={Feb}, pages={1069–1075} } @article{jiang_liang_zheng_liu_wang_wang_zhang_qin_dai_whangbo_et al._2017, title={Photocatalytic reduction of CO2 to methanol by three-dimensional hollow structures of Bi2WO6 quantum dots}, volume={219}, ISSN={["1873-3883"]}, DOI={10.1016/j.apcatb.2017.07.023}, abstractNote={Three-dimensional hollow structures made up of Bi2WO6 quantum dots were prepared by one-pot solvothermal synthesis using ethylene glycol as reactive solvent. The structural, optical and CO2-photoreduction to methanol of these hollow structures were investigated. The ethylene glycol is important not only in assembling the three-dimensional hollow structures but also in suppressing the agglomeration of Bi2WO6 quantum dots. The hollow structure of Bi2WO6 quantum dots has a much higher CO2 adsorption capacity and a wider band gap than does bulk-Bi2WO6, so that the CO2 photoconversion reaction is much faster for the hollow structures made up of Bi2WO6 quantum dots.}, journal={APPLIED CATALYSIS B-ENVIRONMENTAL}, author={Jiang, Zaiyong and Liang, Xizhuang and Zheng, Hailong and Liu, Yuanyuan and Wang, Zeyan and Wang, Peng and Zhang, Xiaoyang and Qin, Xiaoyan and Dai, Ying and Whangbo, Myung-Hwan and et al.}, year={2017}, month={Dec}, pages={209–215} } @article{xu_mace_enriquez_bao_harrell_chen_whangbo_2017, title={Roles of reaction kinetics of CO2 on a PrBaCo2O5.5+delta surfaces}, volume={7}, ISSN={["2046-2069"]}, DOI={10.1039/c7ra06362h}, abstractNote={A symmetric PBCO/YSZ/PBCO cell (where PBCO refers to PrBaCo2O5.5+δ, and YSZ to yttria stabilized zirconia) was designed and fabricated for the investigation of the catalytic nature and reaction kinetics of CO2 on PBCO surfaces.}, number={64}, journal={RSC ADVANCES}, author={Xu, Xing and Mace, Brennan and Enriquez, Erik and Bao, Shanyong and Harrell, Zach and Chen, Chonglin and Whangbo, Myung-Hwan}, year={2017}, pages={40558–40562} } @article{lee_an_gordon_ji_park_shim_lim_whangbo_2017, title={Seebeck Coefficients of Layered BiCuSeO Phases: Analysis of Their Hole-Density Dependence and Quantum Confinement Effect}, volume={29}, ISSN={["1520-5002"]}, DOI={10.1021/acs.chemmater.7b00028}, abstractNote={Hole-doped layered BiCuSeO phases include substitutionally doped Bi1–xAxCuSeO (A = alkali, alkaline earth) as well as vacancy-doped Bi1−δCu1-γSeO and Bi1−δCuSeO. To probe how their Seebeck coefficients are related to their hole density p, we calculated the Seebeck coefficient for defect-free BiCuSeO as a function of the hole density, which is generated by lowering the Fermi level from the valence band maximum (VBM). In addition, we calculated the Seebeck coefficient for Bi1−δCuSeO (δ = 1/32, 1/16) with a large number of Bi vacancies. The Seebeck coefficients of the hole-doped BiCuSeO phases are governed by the electronic states lying within ∼0.5 eV from the VBM. These states are composed of largely Cu 3d xz/yz and Se 4p x/y states and possess the character of a uniform one-dimensional (1D) chain rather than a uniform two-dimensional (2D) lattice expected for a layered phase. The observed S-vs-p relationship for Bi1–xAxCuSeO (A = alkali, alkaline earth) as well as Bi1−δCu1-γSeO (δ = 0, 0.025; γ = 0, 0.025) and Bi1−δCuSeO (δ = 0.0, 0.025) is very well reproduced by the calculated relationship for defect-free BiCuSeO within the rigid band approximation. The observed S-vs-p relationship reflects the quantum confinement effect of uniform 1D chains, despite that the hole-doped BiCuSeO phases consist of 2D layers, (Cu2Se2)2– and (Bi2O2)2+. The drastic decrease in the S values of Bi1−δCuSeO with large δ (= 0.05, 0.075, 0.10) arises from the loss of the quantum confinement effect in the (Cu2Se2)2– layers; that is, the uniform 1D chain character is lost because of their geometry distortion induced by a large number of Bi vacancies.}, number={5}, journal={CHEMISTRY OF MATERIALS}, author={Lee, Changhoon and An, Tae-Ho and Gordon, Elijah E. and Ji, Hyo Seok and Park, Chan and Shim, Ji-Hoon and Lim, Young Soo and Whangbo, Myung-Hwan}, year={2017}, month={Mar}, pages={2348–2354} } @article{koo_gordon_whangbo_2017, title={Single-Domain Ferromagnet of Noncentrosymmetric Uniaxial Magnetic Ions and Magnetoelectric Interaction}, volume={56}, ISSN={["1521-3773"]}, DOI={10.1002/anie.201701699}, abstractNote={The feasibility of a single-domain ferromagnet based on uniaxial magnetic ions was examined. For a noncentrosymmetric uniaxial magnetic ion of magnetic moment at a site of local electric dipole moment p, it is unknown to date whether the magnetic moment prefers to be parallel or antiparallel to the electric dipole moment. The nature of this magnetoelectric interaction was probed in terms of analogical reasoning based on the Rashba effect and density functional calculations. We show that the magnetic and electric dipole moments prefer an antiparallel arrangement, predict that Fe-doped CaZnOS is a single-domain ferromagnet like a bar magnet, and find the probable cause for the ferromagnetism and weak magnetization hysteresis in Fe-doped hexagonal ZnO and ZnS at very low dopant concentrations.}, number={34}, journal={ANGEWANDTE CHEMIE-INTERNATIONAL EDITION}, author={Koo, Hyun-Joo and Gordon, Elijah E. and Whangbo, Myung-Hwan}, year={2017}, month={Aug}, pages={10196–10199} } @article{golubev_dinnebier_schulz_kremer_langbein_senyshyn_law_hansen_koo_whangbo_2017, title={Structural and Magnetic Properties of the Trirutile-type 1D-Heisenberg Anti-Ferromagnet CuTa2O6}, volume={56}, ISSN={["1520-510X"]}, DOI={10.1021/acs.inorgchem.7b00421}, abstractNote={We prepared trirutile-type polycrystalline samples of CuTa2O6 by low-temperature decomposition of a Cu-Ta-oxalate precursor. Diffraction studies at room temperature identified a slight monoclinic distortion of the hitherto surmised tetragonal trirutile crystal structure. Detailed high-temperature X-ray and neutron powder diffraction investigations as well as Raman scattering spectroscopy revealed a structural phase transition at 503(3) K from the monoclinic structure to the tetragonal trirutile structure. GGA+U density functional calculations of the spin-exchange parameters as well as magnetic susceptibility and isothermal magnetization measurements reveal that CuTa2O6 is a new 1D Heisenberg magnet with predominant anti-ferromagnetic nearest-neighbor intrachain spin-exchange interaction of ∼50 K. Interchain exchange is a factor of ∼5 smaller. Heat capacity and low-temperature high-intensity neutron powder diffraction studies could not detect long-range order down to 0.45 K.}, number={11}, journal={INORGANIC CHEMISTRY}, author={Golubev, Aleksandr and Dinnebier, Robert E. and Schulz, Armin and Kremer, Reinhard K. and Langbein, Hubert and Senyshyn, Anatoliy and Law, Joseph M. and Hansen, Thomas C. and Koo, Hyun-Joo and Whangbo, Myung-Hwan}, year={2017}, month={Jun}, pages={6318–6329} } @article{cheng_gordon_whangbo_deng_2017, title={Superconductivity Induced by Oxygen Doping in Y2O2Bi}, volume={56}, ISSN={["1521-3773"]}, DOI={10.1002/anie.201701427}, abstractNote={Abstract When doped with oxygen, the layered Y 2 O 2 Bi phase becomes a superconductor. This finding raises questions about the sites for doped oxygen, the mechanism of superconductivity, and practical guidelines for discovering new superconductors. We probed these questions in terms of first‐principles calculations for undoped and O‐doped Y 2 O 2 Bi. The preferred sites for doped O atoms are the centers of Bi 4 squares in the Bi square net. Several Bi 6p x / y bands of Y 2 O 2 Bi are raised in energy by oxygen doping because the 2p x / y orbitals of the doped oxygen make antibonding possible with the 6p x / y orbitals of surrounding Bi atoms. Consequently, the condition necessary for the “flat/steep” band model for superconductivity is satisfied in O‐doped Y 2 O 2 Bi.}, number={34}, journal={ANGEWANDTE CHEMIE-INTERNATIONAL EDITION}, author={Cheng, Xiyue and Gordon, Elijah E. and Whangbo, Myung-Hwan and Deng, Shuiquan}, year={2017}, month={Aug}, pages={10123–10126} } @article{xu_an_liu_huang_qin_zhang_dai_whangbo_2016, title={An efficient visible-light photocatalyst made from a nonpolar layered semiconductor by grafting electron-withdrawing organic molecules to its surface}, volume={52}, ISSN={["1364-548X"]}, DOI={10.1039/c6cc07849d}, abstractNote={A nonpolar inorganic layered semiconductor becomes an efficient visible-light photocatalyst when its surface layer becomes polar by chemically attaching electron-withdrawing 4-substituted thiophenolates -S-C6H4Z (Z = NO2, COOH, Cl, Br, H, CH3, NH2) via Bi-S bonds. An in-depth study finds a correlation between the apparent rate constant (kapp) and the Hammett constants σpara of the 4-substituted groups.}, number={92}, journal={CHEMICAL COMMUNICATIONS}, author={Xu, Benyan and An, Yang and Liu, Yuanyuan and Huang, Baibiao and Qin, Xiaoyan and Zhang, Xiaoyang and Dai, Ying and Whangbo, Myung-Hwan}, year={2016}, pages={13507–13510} } @misc{stroppa_barone_di sante_cuoco_picozzi_whangbo_2016, title={Analogies between Jahn-Teller and Rashba spin physics}, volume={116}, ISSN={["1097-461X"]}, DOI={10.1002/qua.25209}, abstractNote={Abstract In developing physical theories, analogical reasoning has been found to be very powerful, as attested by a number of important historical examples. An analogy between two apparently different phenomena, once established, allows one to transfer information and bring new concepts from one phenomenon to the other. Here, we discuss an important analogy between two widely different physical problems, namely, the Jahn–Teller distortion in molecular physics and the Rashba spin splitting in condensed matter physics. By exploring their conceptual and mathematical features and by searching for the counterparts between them, we examine the orbital texture in Jahn–Teller systems, as the counterpart of the spin texture of the Rashba physics, and put forward a possible way of experimentally detecting the orbital texture. Finally, we discuss the analogy by comparing the coexistence of linear Rashba + Dresselhaus effects and Jahn–Teller problems for specific symmetries, which allow for nontrivial spin and orbital textures, respectively.}, number={20}, journal={INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY}, author={Stroppa, Alessandro and Barone, Paolo and Di Sante, Domenico and Cuoco, Mario and Picozzi, Silvia and Whangbo, Myung-Hwan}, year={2016}, month={Oct}, pages={1442–1450} } @article{kovrugin_gordon_kasapbasi_whangbo_colmont_siidra_colis_krivovichev_mentre_2016, title={Bonding Scheme, Hydride Character, and Magnetic Paths of (HPO3)(2-) Versus (SeO3)(2-) Building Units in Solids}, volume={120}, ISSN={["1932-7447"]}, DOI={10.1021/acs.jpcc.5b10889}, abstractNote={The abilities of the (HPO3)2– and (SeO3)2– anions as structure building units and as spin exchange paths between magnetic ions were investigated by preparing and analyzing the isostructural Fe2(SeO3)3 and Fe2(HPO3)3. In both compounds, the face-sharing Fe2O9 dimers are interconnected into chains by the (HPO3)2– and (SeO3)2– anions. The (HPO3)2– is the structural counterpart of the Se electron lone pair of (SeO3)2– due to the weak hydride character of the terminal hydrogen. However, they differ considerably as spin exchange paths between magnetic cations. Both compounds exhibit an effective magnetic dimer behavior, unexpectedly arising from the interdimer Fe—O···O—Fe exchange along the chain, but weaker in Fe2(HPO3)3 by a factor of ∼3. It is consistent with the general tendencies of the phosphite anions to act as a weak magnetic mediator, which is caused by the through-bond effect of the P3+ ion in the Fe—O···P3+···O—Fe exchange path, much weaker than in the selenite phase in absence of P3+d contribution. Reasons for stronger exchanges through phosphates or sulfates are also discussed.}, number={3}, journal={JOURNAL OF PHYSICAL CHEMISTRY C}, author={Kovrugin, Vadim M. and Gordon, Elijah E. and Kasapbasi, Esra E. and Whangbo, Myung-Hwan and Colmont, Marie and Siidra, Oleg I. and Colis, Silviu and Krivovichev, Sergey V. and Mentre, Olivier}, year={2016}, month={Jan}, pages={1650–1656} } @article{caslin_kremer_razavi_hanfland_syassen_gordon_whangbo_2016, title={Competing Jahn-Teller distortions and hydrostatic pressure effects in the quasi-one-dimensional quantum ferromagnet CuAs2O4}, volume={93}, ISSN={["1550-235X"]}, DOI={10.1103/physrevb.93.022301}, abstractNote={${\mathrm{CuAs}}_{2}{\mathrm{O}}_{4}$ is a $S=1/2$ quasi-one-dimensional ribbon chain compound which orders ferromagnetically at 7.4 K under ambient conditions. ${\mathrm{CuAs}}_{2}{\mathrm{O}}_{4}$ features nearest- and next-nearest-neighbor spin-exchange interactions along the spin chains with a ratio $\ensuremath{\alpha}={J}_{\mathrm{nn}}/{J}_{\mathrm{nnn}}$ in close proximity to the quantum critical point at $\ensuremath{\alpha}=\ensuremath{-}4$. We apply hydrostatic pressure up to $\ensuremath{\sim}11.5$ GPa and examine the structural and magnetic properties using Raman spectroscopy, single-crystal synchrotron x-ray diffraction, and magnetic susceptibility measurements. External pressure severely reduces the axial Jahn-Teller elongations of the oxygen octahedra surrounding the ${\mathrm{Cu}}^{2+}$ cations and stabilizes the ferromagnetic ground state. At 9.2(2) GPa, we detect a structural phase transition leading to an increased twisting of the ${\mathrm{CuO}}_{2}$ ribbon chains and a large drop of the magnetic ordering temperature. Ab initio density functional theory calculations of the spin-exchange parameters, using the structural parameters as a function of pressure, support the experimental findings.}, number={2}, journal={PHYSICAL REVIEW B}, author={Caslin, K. and Kremer, R. K. and Razavi, F. S. and Hanfland, M. and Syassen, K. and Gordon, E. E. and Whangbo, M. -H.}, year={2016}, month={Jan} } @article{gordon_kohler_whangbo_2016, title={Condensed-matter equation of states covering a wide region of pressure studied experimentally}, volume={6}, journal={Scientific Reports}, author={Gordon, E. E. and Kohler, J. and Whangbo, M. H.}, year={2016} } @article{jiang_liu_jing_huang_zhang_qin_dai_whangbo_2016, title={Enhancing the Photocatalytic Activity of BiVO4 for Oxygen Evolution by Ce Doping: Ce3+ Ions as Hole Traps}, volume={120}, ISSN={["1932-7455"]}, DOI={10.1021/acs.jpcc.5b10856}, abstractNote={To enhance the photocatalytic activity of monoclinic BiVO4 for O2 evolution from water, Ce-doped BiVO4 was prepared using the one-pot facile solvothermal method and characterized via XRD, Raman, XPS, and electrochemical impedance spectroscopy (EIS). The XPS spectra confirm that Ce component is Ce3+ ions instead of Ce4+ ions. From the structural characterization and the calculations of formation energies it has been stated that the doping of Ce3+ ions takes place at Bi3+ sites without changing the host structure. The as-prepared Ce-doped BiVO4 samples display significantly enhanced photocatalytic O2 evolution activities from water compared to pristine BiVO4. Density of states calculations indicate that Ce3+ ions act as hole traps, thereby delaying the recombination of photogenerated electrons and holes. The results demonstrate that the substitution of the remaining monoclinic crystal structure may offer an attractive alternative approach for the doping of BiVO4 to enhance the evolution activity of photocatalytic O2.}, number={4}, journal={JOURNAL OF PHYSICAL CHEMISTRY C}, author={Jiang, Zaiyong and Liu, Yuanyuan and Jing, Tao and Huang, Baibiao and Zhang, Xiaoyang and Qin, Xiaoyan and Dai, Ying and Whangbo, Myung-Hwan}, year={2016}, month={Feb}, pages={2058–2063} } @article{lee_hong_son_kan_shim_whangbo_2016, title={Magnetic structure of (C5H12N)CuBr3: origin of the uniform Heisenberg chain behavior and the magnetic anisotropy of the Cu2+ (S=1/2) ions}, volume={6}, ISSN={["2046-2069"]}, DOI={10.1039/c5ra26341g}, abstractNote={The AFM chain behavior observed for (pipH)CuBr3is not caused by the CuBr3chains, but by the interchain exchanges leading to two-leg spin ladders. The Cu2+ions have easy-axis anisotropy, and this arises largely from the SOC of the Br−ligands.}, number={27}, journal={RSC ADVANCES}, author={Lee, Changhoon and Hong, Jisook and Son, Won-joon and Kan, Erjun and Shim, Ji Hoon and Whangbo, Myung-Hwan}, year={2016}, pages={22722–22727} } @article{bruyer_di sante_barone_stroppa_whangbo_picozzi_2016, title={Possibility of combining ferroelectricity and Rashba-like spin splitting in monolayers of the 1T-type transition-metal dichalcogenides MX2 (M = Mo, W; X = S, Se, Te)}, volume={94}, ISSN={["2469-9969"]}, DOI={10.1103/physrevb.94.195402}, abstractNote={First-principles calculations were carried out to explore the possible coupling between spin-polarized electronic states and ferroelectric polarization in monolayers of transition-metal dichalcogenides $M{X}_{2}$ ($M=\mathrm{Mo},\mathrm{W};X=\mathrm{S},\mathrm{Se},\mathrm{Te})$ with distorted octahedrally coordinated $1T$ structures. For ${d}^{2}$ metal ions, two competing metal clustering effects can take place, where metal ions are arranged in trimers or zigzag chains. Among these, the former structural distortion comes along with an improper ferroelectric phase which persists in the monolayer limit. Switchable Rashba-like spin-polarization features are predicted in the trimerized polytype, which can be permanently tuned by acting on its ferroelectric properties. The polar trimerized structure is found to be stable for $1T\ensuremath{-}{\mathrm{MoS}}_{2}$ only, while the nonpolar polytype with zigzag metal clustering is predicted to stabilize for other transition-metal dichalcogenides with ${d}^{2}$ metal ions.}, number={19}, journal={PHYSICAL REVIEW B}, author={Bruyer, Emilie and Di Sante, Domenico and Barone, Paolo and Stroppa, Alessandro and Whangbo, Myung-Hwan and Picozzi, Silvia}, year={2016}, month={Nov} } @article{gordon_xiang_kohler_whangbo_2016, title={Spin orientations of the spin-half Ir4+ ions in Sr3NiIrO6, Sr2IrO4, and Na2IrO3: Density functional, perturbation theory, and Madelung potential analyses}, volume={144}, number={11}, journal={Journal of Chemical Physics}, author={Gordon, E. E. and Xiang, H. J. and Kohler, J. and Whangbo, M. H.}, year={2016} } @article{kenneth r. o'neal_holinsworth_chen_peterson_carreiro_lee_manson_whangbo_li_liu_et al._2016, title={Spin-Lattice Coupling in [Ni(HF2)(pyrazine)(2)]SbF6 Involving the HF2- Superexchange Pathway}, volume={55}, ISSN={["1520-510X"]}, DOI={10.1021/acs.inorgchem.6b01679}, abstractNote={Magnetoelastic coupling in the quantum magnet [Ni(HF2)(pyrazine)2]SbF6 has been investigated via vibrational spectroscopy using temperature, magnetic field, and pressure as tuning parameters. While pyrazine is known to be a malleable magnetic superexchange ligand, we find that HF2- is surprisingly sensitive to external stimuli and is actively involved in both the magnetic quantum phase transition and the series of pressure-induced structural distortions. The amplified spin-lattice interactions involving the bifluoride ligand can be understood in terms of the relative importance of the intra- and interplanar magnetic energy scales.}, number={23}, journal={INORGANIC CHEMISTRY}, author={Kenneth R. O'Neal and Holinsworth, Brian S. and Chen, Zhiguo and Peterson, Peter K. and Carreiro, Kimberly E. and Lee, Changhoon and Manson, Jamie L. and Whangbo, Myung-Hwan and Li, Zhigiang and Liu, Zhenxian and et al.}, year={2016}, month={Dec}, pages={12172–12178} } @article{gordon_xu_xiang_bussmann-holder_kremer_simon_koehler_whangbo_2016, title={Structure and Composition of the 200K-Superconducting Phase of H2S at Ultrahigh Pressure: The Perovskite (SH-)(H3S+)}, volume={55}, ISSN={["1521-3773"]}, DOI={10.1002/anie.201511347}, abstractNote={Abstract At ultrahigh pressure (>110 GPa), H 2 S is converted into a metallic phase that becomes superconducting with a record T c of approximately 200 K. It has been proposed that the superconducting phase is body‐centered cubic H 3 S (Im m, a=3.089 Å) resulting from the decomposition reaction 3 H 2 S→2 H 3 S+S. The analogy between H 2 S and H 2 O led us to a very different conclusion. The well‐known dissociation of water into H 3 O + and OH − increases by orders of magnitude under pressure. H 2 S is anticipated to behave similarly under pressure, with the dissociation process 2 H 2 S→H 3 S + +SH − leading to the perovskite structure (SH − )(H 3 S + ). This phase consists of corner‐sharing SH 6 octahedra with SH − ions at each A site (the centers of the S 8 cubes). DFT calculations show that the perovskite (SH − )(H 3 S + ) is thermodynamically more stable than the Im m structure of H 3 S, and suggest that the A site hydrogen atoms are most likely fluxional even at T c .}, number={11}, journal={ANGEWANDTE CHEMIE-INTERNATIONAL EDITION}, author={Gordon, Elijah E. and Xu, Ke and Xiang, Hongjun and Bussmann-Holder, Annette and Kremer, Reinhard K. and Simon, Arndt and Koehler, Juergen and Whangbo, Myung-Hwan}, year={2016}, month={Mar}, pages={3682–3684} } @article{bao_xu_enriquez_mace_chen_kelliher_chen_zhang_whangbo_dong_et al._2015, title={Atomically layer-by-layer diffusion of oxygen/hydrogen in highly epitaxial PrBaCo2O5.5+delta thin films}, volume={107}, number={24}, journal={Applied Physics Letters}, author={Bao, S. Y. and Xu, X. and Enriquez, E. and Mace, B. E. and Chen, G. and Kelliher, S. P. and Chen, C. L. and Zhang, Y. M. and Whangbo, M. H. and Dong, C. and et al.}, year={2015} } @article{enriquez_xu_bao_harrell_chen_choi_jun_kim_whangbo_2015, title={Catalytic Dynamics and Oxygen Diffusion in Doped PrBaCo2O5.5+delta Thin Films}, volume={7}, ISSN={["1944-8252"]}, DOI={10.1021/acsami.5b07688}, abstractNote={The Sr and Fe codoped double perovskites PrBaCo2O5.5+δ (PrBCO) thin films of Pr(Ba0.5Sr0.5)(Co1.5Fe0.5)O5.5+δ (PBSCFO) were epitaxially grown for chemical catalytic studies. The resistance behavior of PBSCFO epitaxial films was monitored under the switching flow of reducing and oxidizing gases as a function of the gas flow time, t, using an electrical conductivity relaxation (ECR) experimental setup. The R(t) vs t relationships determined at various temperatures show the occurrence of two oxidation processes, Co2+/Co3+ ↔ Co3+ and Co3+ ↔ Co3+/Co4+. Mathematical fitting of the observed R(t) vs t relationships was carried out using Fick’s second law for one-dimensional diffusion of charge carriers to derive the diffusivity D(T) and τ(T) for the two processes at various temperatures, T. The D(T) vs T relationships were analyzed in terms of the Arrhenius relationship to find the activation energies Ea for each process. Oscillations in the dR(t)/dt plots, observed under oxidation reactions, were discussed in terms of a layer-by-layer oxygen vacancy exchange diffusion mechanism. Our work suggests that thin films of LnBCO (Ln = lanthanide) with their A and B sites doped as in PBSCFO are excellent candidates for the development of low or intermediate temperature energy conversion devices and gas sensor applications.}, number={43}, journal={ACS APPLIED MATERIALS & INTERFACES}, author={Enriquez, Erik and Xu, Xing and Bao, Shanyong and Harrell, Zach and Chen, Chonglin and Choi, Sihyuk and Jun, Areum and Kim, Guntae and Whangbo, Myung-Hwan}, year={2015}, month={Nov}, pages={24353–24359} } @article{zvereva_presniakov_whangbo_koo_frantsuzenko_savelieva_sobolev_nalbandyan_shih_chiang_et al._2015, title={Crucial Role of Site Disorder and Frustration in Unusual Magnetic Properties of Quasi-2D Triangular Lattice Antimonate Na4FeSbO6}, volume={46}, ISSN={["1613-7507"]}, DOI={10.1007/s00723-015-0700-5}, number={10}, journal={APPLIED MAGNETIC RESONANCE}, author={Zvereva, Elena A. and Presniakov, Igor A. and Whangbo, Myung-Hwan and Koo, Hyun-Joo and Frantsuzenko, Tatyana V. and Savelieva, Olga A. and Sobolev, Alexey V. and Nalbandyan, Vladimir B. and Shih, Pei-Shan and Chiang, Jen-Che and et al.}, year={2015}, month={Oct}, pages={1121–1145} } @article{wei_dai_huang_li_naegele_over_whangbo_jacob_2015, title={Density Functional Characterization of the Electronic Structures and Band Bending of Rutile RuO2/TiO2(110) Heterostructures}, volume={119}, ISSN={["1932-7447"]}, DOI={10.1021/acs.jpcc.5b01884}, abstractNote={The enhanced catalytic and photocatalytic activities of a RuO2 layer deposited on the TiO2(110) surface were examined by constructing model RuO2/TiO2(110) heterostructures with and without oxygen vacancies and performing density functional calculations. The formation of the heterojunction only weakly affects the atomic structure of the interface due to a pseudomorphic deposition but causes a strong electron density accumulation in the interface as well as a bending of the valence and conduction bands of TiO2. The electron accumulation in the interface creates a strong internal electric field, which helps to effectively separate photogenerated electron–hole pairs during a photocatalytic process. Finally, we report on the catalytic role of oxygen vacancies at the surface.}, number={22}, journal={JOURNAL OF PHYSICAL CHEMISTRY C}, author={Wei, Wei and Dai, Ying and Huang, Baibiao and Li, Xiaoke and Naegele, Florian and Over, Herbert and Whangbo, Myung-Hwan and Jacob, Timo}, year={2015}, month={Jun}, pages={12394–12399} } @article{di sante_stroppa_barone_whangbo_picozzi_2015, title={Emergence of ferroelectricity and spin-valley properties in two-dimensional honeycomb binary compounds}, volume={91}, ISSN={["2469-9969"]}, DOI={10.1103/physrevb.91.161401}, abstractNote={By means of density functional theory calculations, we predict that several two dimensional AB binary monolayers, where A and B atoms belong to group IV or III-V, are ferroelectric. Dipoles arise from the buckled structure, where the A and B ions are located on the sites of a bipartite corrugated honeycomb lattice with trigonal symmetry. We discuss the emerging valley-dependent properties and the coupling of spin and valley physics, which arise from the loss of inversion symmetry, and explore the interplay between ferroelectricity and Rashba spin-spitting phenomena. We show that valley-related properties originate mainly from the binary nature of AB monolayers, while the Rashba spin-texture developing around valleys is fully controllable and switchable by reversing the ferroelectric polarization.}, number={16}, journal={PHYSICAL REVIEW B}, author={Di Sante, Domenico and Stroppa, Alessandro and Barone, Paolo and Whangbo, Myung-Hwan and Picozzi, Silvia}, year={2015}, month={Apr} } @article{li_jing_liu_huang_dai_zhang_qin_whangbo_2015, title={Enhancing the Efficiency of Water Oxidation by Boron-Doped BiVO4 under Visible Light: Hole Trapping by BO4 Tetrahedra}, volume={80}, ISSN={["2192-6506"]}, DOI={10.1002/cplu.201500110}, abstractNote={Abstract Boron‐doped monoclinic and tetragonal phases of BiVO 4 were prepared by using the urea precipitation method, and the visible‐light photocatalytic activities of pristine and boron‐doped BiVO 4 for oxygen generation from water were compared. Boron doping enhances the photocatalytic activities of BiVO 4 . The reasons for this enhancement were probed by performing X‐ray photoelectron, Raman, and electrochemical impedance spectroscopy measurements, and also by performing density functional calculations for model boron‐doped BiVO 4 structures. The photocatalytic activities of BiVO 4 is enhanced by boron doping because the resulting BO 4 tetrahedra, which are smaller than the VO 4 tetrahedra, create an occupied defect level per boron lying approximately 0.17 eV above the valence‐band maximum of pristine BiVO 4 , and this defect level is localized because it is made up of the O 2 p levels of the BO 4 tetrahedron. Thus, the BO 4 tetrahedra that result from boron doping act as hole traps, thereby slowing down the recombination of photogenerated electrons and holes.}, number={7}, journal={CHEMPLUSCHEM}, author={Li, Yanqing and Jing, Tao and Liu, Yuanyuan and Huang, Baibiao and Dai, Ying and Zhang, Xiaoyang and Qin, Xiaoyan and Whangbo, Myung-Hwan}, year={2015}, month={Jul}, pages={1113–1118} } @article{ma_dai_wei_huang_whangbo_2015, title={Insights into How Fluorine-Adsorption and n-Type Doping Affect the Relative Stability of the (001) and (101) Surfaces of TiO2: Enhancing the Exposure of More Active but Thermodynamically Less Stable (001)}, volume={6}, ISSN={["1948-7185"]}, DOI={10.1021/acs.jpclett.5b00595}, abstractNote={The stability of both the pure and fluorine (F)-adsorbed surface of TiO2 is examined on the basis of density functional calculations. For pure surfaces, both the beneficial local geometric structures and local potential strengthen the Ti-O binding in (101), rendering it the most stable surface. For F-adsorbed surfaces, F-adsorption significantly weakens the Ti-O bonds in (101) but strengthens them in (001), so that (001) becomes more stable than (101) for the F-adsorbed surfaces. On the basis of this observation, we further show that the n-type doping in TiO2 can significantly decrease the ability of F-adsorption in switching the relative stability of the two surfaces. The present work not only provides new insights into the physical and chemical properties about both pure and F-adsorbed surfaces of TiO2 and conclusively explains related experimental results but also suggests viable ways to prepare TiO2 samples with a high percentage of (001).}, number={10}, journal={JOURNAL OF PHYSICAL CHEMISTRY LETTERS}, author={Ma, Xiangchao and Dai, Ying and Wei, Wei and Huang, Baibiao and Whangbo, Myung-Hwan}, year={2015}, month={May}, pages={1876–1882} } @article{wei_dai_huang_whangbo_jacob_2015, title={Loss of Linear Band Dispersion and Trigonal Structure in Silicene on Ir(111)}, volume={6}, ISSN={["1948-7185"]}, DOI={10.1021/acs.jpclett.5b00106}, abstractNote={The structure of silicene/Ir(111) was examined on the basis of density functional theory. We have found that Ir(111) preserves the 2D character of silicene but significantly distorts its structure from the trigonal one expected for an isolated silicene. The electronic structure of silicene is strongly hybridized with that of Ir(111) so that silicene on Ir(111) loses its linear band dispersion around the Fermi level, giving rise to a metallic band structure; however, silicene/Ir(111) exhibits a hidden linear-dispersive band, which is related to the linear-dispersive conduction band of an isolated silicene.}, number={6}, journal={JOURNAL OF PHYSICAL CHEMISTRY LETTERS}, author={Wei, Wei and Dai, Ying and Huang, Baibiao and Whangbo, Myung-Hwan and Jacob, Timo}, year={2015}, month={Mar}, pages={1065–1070} } @article{zvereva_nalbandyan_evstigneeva_koo_whangbo_ushakov_medvedev_medvedeva_gridina_yalovega_et al._2015, title={Magnetic and electrode properties, structure and phase relations of the layered triangular-lattice tellurate Li4NiTeO6}, volume={225}, ISSN={["1095-726X"]}, DOI={10.1016/j.jssc.2014.12.003}, abstractNote={Abstract We examined the magnetic properties of layered oxide Li4NiTeO6 by magnetic susceptibility, magnetization and ESR measurements and density functional calculations, and characterized phase relations, crystal structure and electrochemical properties of Li4NiTeO6. The magnetization and ESR data indicate the absence of a long-range magnetic order down to 1.8 K, and the magnetic susceptibility data the presence of dominant antiferromagnetic interactions. These observations are well accounted for by density functional calculations, which show that the spin exchanges of the LiNiTeO6 layers in Li4NiTeO6 are strongly spin frustrated. The electrochemical charging of Li4NiTeO6 takes place at constant potential of ca. 4.2 V vs. Li/Li+ indicating two-phase process as confirmed by X-rays. The starting phase is only partially recovered on discharge due to side reactions.}, journal={JOURNAL OF SOLID STATE CHEMISTRY}, author={Zvereva, Elena A. and Nalbandyan, Vladimir B. and Evstigneeva, Maria A. and Koo, Hyun-Joo and Whangbo, Myung-Hwan and Ushakov, Arseni V. and Medvedev, Boris S. and Medvedeva, Larisa I. and Gridina, Nelly A. and Yalovega, Galina E. and et al.}, year={2015}, month={May}, pages={89–96} } @article{nalbandyan_zvereva_nikulin_shukaev_whangbo_koo_abdel-hafiez_chen_koo_vasiliev_et al._2015, title={New Phase of MnSb2O6 Prepared by Ion Exchange: Structural, Magnetic, and Thermodynamic Properties}, volume={54}, ISSN={["1520-510X"]}, DOI={10.1021/ic502666c}, abstractNote={A new layered trigonal (P3̅1m) form of MnSb2O6, isostructural with MSb2O6 (M = Cd, Ca, Sr, Pb, and Ba) and MAs2O6 (M = Mn, Co, Ni, and Pd), was prepared by ion-exchange reaction between ilmenite-type NaSbO3 and MnSO4–KCl–KBr melt at 470 °C. It is characterized by Rietveld analysis of the X-ray diffraction pattern, electron microprobe analysis, magnetic susceptibility, specific heat, and ESR measurements as well as by density functional theory calculations. MnSb2O6 is very similar to MnAs2O6 in the temperature dependence of their magnetic susceptibility and spin exchange interactions. The magnetic susceptibility and specific heat data show that MnSb2O6 undergoes a long-range antiferromagnetic order with Néel temperature TN = 8.5(5) K. In addition, a weak ferromagnetic component appears below T1 = 41.5(5) K. DFT+U implies that the main spin exchange interactions are antiferromagnetic, thereby forming spin-frustrated triangles. The long-range ordered magnetic structure of MnSb2O6 is predicted to be incommensurate as found for MnAs2O6. On heating, the new phase transforms to the stable P321 form via its intermediate disordered variant.}, number={4}, journal={INORGANIC CHEMISTRY}, author={Nalbandyan, Vladimir B. and Zvereva, Elena A. and Nikulin, Alexey Yu and Shukaev, Igor L. and Whangbo, Myung-Hwan and Koo, Hyun-Joo and Abdel-Hafiez, Mahmoud and Chen, Xiao-Jia and Koo, Changhyun and Vasiliev, Alexander N. and et al.}, year={2015}, month={Feb}, pages={1705–1711} } @article{wang_huang_li_wang_qin_zhang_dai_whangbo_2015, title={On Structural Features Necessary for Near-IR-Light Photocatalysts}, volume={21}, ISSN={["1521-3765"]}, DOI={10.1002/chem.201501477}, abstractNote={In the search for photocatalysts that can directly utilize near-IR (NIR) light, we investigated three oxides Cu3(OH)4SO4 (antlerite), Cu4(OH)6SO4, and Cu2(OH)3Cl by photodecomposing 2,4-dichlorophenol over them under NIR irradiation and by comparing their electronic structures with that of the known NIR photocatalyst Cu2(OH)PO4. Both Cu3(OH)4SO4 and Cu4(OH)6SO4 are NIR photocatalysts, but Cu2(OH)3Cl is not. Thus, in addition to the presence of two different CuOm and Cu'On polyhedra linked with Cu-O-Cu' bridges, the presence of acceptor groups (e.g., SO4, PO4) linked to the metal oxygen polyhedra is necessary for NIR photocatalysts.}, number={39}, journal={CHEMISTRY-A EUROPEAN JOURNAL}, author={Wang, Gang and Huang, Baibiao and Li, Zhujie and Wang, Zeyan and Qin, Xiaoyan and Zhang, Xiaoyang and Dai, Ying and Whangbo, Myung-Hwan}, year={2015}, month={Sep}, pages={13583–13587} } @article{kim_yu_kim_koo_whangbo_2015, title={On Why the Two Polymorphs of NaFePO4 Exhibit Widely Different Magnetic Structures: Density Functional Analysis}, volume={54}, ISSN={["1520-510X"]}, DOI={10.1021/acs.inorgchem.5b00577}, abstractNote={Triphylite-NaFePO4 is a cathode material for Na(+)-ion batteries, whereas its alternative polymorph maricite-NaFePO4 is not. These two different polymorphs exhibit widely different magnetic structures; the ordered magnetic structure of triphylite-NaFePO4 below ∼50 K is described by the propagation vector q1 = (0, 0, 0) with collinear spins, and that of maricite-NaFePO4 below ∼13 K is described by q2 = (1/2, 0, 1/2) with noncollinear spins. We probed the causes for these differences by calculating the spin exchange interactions of the two polymorphs and determining the preferred orientations of their high-spin Fe(2+) (d(6), S = 2) ions on the basis of density functional calculations. Our study shows that maricite-NaFePO4 is not spin-frustrated, which is also the case for triphylite-NaFePO4, that the ordered magnetic structure of triphylite-NaFePO4 is determined mainly by spin exchange, whereas that of maricite-NaFePO4 is determined by both spin exchange and magnetic anisotropy, and that the preferred spin orientations in the two polymorphs can be explained by perturbation theory using spin-orbit coupling as the perturbation.}, number={10}, journal={INORGANIC CHEMISTRY}, author={Kim, Hee Hwan and Yu, Il Han and Kim, Hoon Sik and Koo, Hyun-Joo and Whangbo, Myung-Hwan}, year={2015}, month={May}, pages={4966–4971} } @article{lee_hong_stroppa_whangbo_shim_2015, title={Organic-inorganic hybrid perovskites ABI(3) (A = CH3NH3, NH2CHNH2; B = Sn, Pb) as potential thermoelectric materials: a density functional evaluationt}, volume={5}, ISSN={["2046-2069"]}, DOI={10.1039/c5ra12536g}, abstractNote={Our calculations show that, when doped by electrons, the organic–inorganic perovskite iodides ABI3(A = CH3NH3, NH2CHNH2; B = Sn, Pb) can be a good thermoelectric material with thermoelectric efficiency comparable to that of hole-doped Bi2Te3.}, number={96}, journal={RSC ADVANCES}, author={Lee, Changhoon and Hong, Jisook and Stroppa, Alessandro and Whangbo, Myung-Hwan and Shim, Ji Hoon}, year={2015}, pages={78701–78707} } @article{galliez_deniard_payen_lambertin_bart_koo_whangbo_jobic_2015, title={Pair Distribution Function and Density Functional Theory Analyses of Hydrogen Trapping by gamma-MnO2}, volume={54}, ISSN={["1520-510X"]}, DOI={10.1021/ic5026334}, abstractNote={In the presence of "Ag2O" as a promoter, γ-MnO2 traps dihydrogen in its (2 × 1) and (1 × 1) tunnels. The course of this reaction was examined by analyzing the X-ray diffraction patterns of the HxMnO2/"Ag2O" system (0 ≤ x < 1) on the basis of pair distribution function and density functional theory (DFT) analyses. Hydrogen trapping occurs preferentially in the (2 × 1) tunnels of γ-MnO2, which is then followed by that in the (1 × 1) tunnels. Our DFT analysis shows that this process is thermodynamically favorable.}, number={4}, journal={INORGANIC CHEMISTRY}, author={Galliez, Kevin and Deniard, Philippe and Payen, Christophe and Lambertin, David and Bart, Florence and Koo, Hyun-Joo and Whangbo, Myung-Hwan and Jobic, Stephane}, year={2015}, month={Feb}, pages={1194–1196} } @misc{whangbo_gordon_xiang_koo_lee_2015, title={Prediction of Spin Orientations in Terms of HOMO-LUMO Interactions Using Spin-Orbit Coupling as Perturbation}, volume={48}, ISSN={["1520-4898"]}, DOI={10.1021/acs.accounts.5b00408}, abstractNote={For most chemists and physicists, electron spin is merely a means needed to satisfy the Pauli principle in electronic structure description. However, the absolute orientations of spins in coordinate space can be crucial in understanding the magnetic properties of materials with unpaired electrons. At low temperature, the spins of a magnetic solid may undergo long-range magnetic ordering, which allows one to determine the directions and magnitudes of spin moments by neutron diffraction refinements. The preferred spin orientation of a magnetic ion can be predicted on the basis of density functional theory (DFT) calculations including electron correlation and spin-orbit coupling (SOC). However, most chemists and physicists are unaware of how the observed and/or calculated spin orientations are related to the local electronic structures of the magnetic ions. This is true even for most crystallographers who determine the directions and magnitudes of spin moments because, for them, they are merely the parameters needed for the diffraction refinements. The objective of this article is to provide a conceptual framework of thinking about and predicting the preferred spin orientation of a magnetic ion by examining the relationship between the spin orientation and the local electronic structure of the ion. In general, a magnetic ion M (i.e., an ion possessing unpaired spins) in a solid or a molecule is surrounded with main-group ligand atoms L to form an MLn polyhedron, where n is typically 4-6, and the d states of MLn are split because the antibonding interactions of the metal d orbitals with the p orbitals of the surrounding ligands L depend on the symmetries of the orbitals involved.1 The magnetic ion M of MLn has a certain preferred spin direction because its split d states interact among themselves under SOC.2,3 The preferred spin direction can be readily predicted on the basis of perturbation theory in which the SOC is taken as perturbation and the split d states as unperturbed states by inspecting the magnetic quantum numbers of its d orbitals present in the HOMO and LUMO of the MLn polyhedron. This is quite analogous to how chemists predict whether a chemical reaction is symmetry-allowed or symmetry-forbidden in terms of the HOMO-LUMO interactions by simply inspecting the symmetries of the frontier orbitals.4,5 Experimentally, the determination of the preferred spin orientations of magnetic ions requires a sophisticated level of experiments, for example, neutron diffraction measurements for magnetic solids with an ordered spin state at a very low temperature. Theoretically, it requires an elaborate level of electronic structure calculations, namely, DFT calculations including electron correlation and SOC. We show that the outcomes of such intricate experimental measurements and theoretical calculations can be predicted by a simple perturbation theory analysis.}, number={12}, journal={ACCOUNTS OF CHEMICAL RESEARCH}, author={Whangbo, Myung-Hwan and Gordon, Elijah E. and Xiang, Hongjun and Koo, Hyun-Joo and Lee, Changhoon}, year={2015}, month={Dec}, pages={3080–3087} } @article{lee_kim_kim_rhee_whangbo_2015, title={Solution phase post-modification of a trimesic acid network on Au(111) with Zn2+ ions}, volume={51}, ISSN={["1364-548X"]}, DOI={10.1039/c4cc08621j}, abstractNote={Solution phase post-modification of a trimesic acid (TMA) network on Au(111) with Zn(2+) ions was found to induce transformation of a bar-featured scanning tunneling microscopy image of (5√3 × 5√3) to a chevron-pair image of (10√3 × 10√3). Voltammetric determination of Zn coverage in the modified TMA network supports the fact that the chevron feature consists of three TMA molecules combined via two coordination bonds between Zn(2+) ions and carboxylates of TMA.}, number={5}, journal={CHEMICAL COMMUNICATIONS}, author={Lee, Jaesung and Kim, Jandee and Kim, Hyeran and Rhee, Choong Kyun and Whangbo, Myung-Hwan}, year={2015}, pages={873–876} } @article{canevet_fak_kremer_chun_enderle_gordon_bettis_whangbo_taylor_adroja_2015, title={Spin excitations in the two-dimensional strongly coupled dimer system malachite}, volume={91}, ISSN={["1550-235X"]}, DOI={10.1103/physrevb.91.060402}, abstractNote={The mineral malachite, $\mathrm{Cu}{}_{2}(\mathrm{OD}){}_{2}\mathrm{CO}{}_{3}$, has a quantum spin-liquid ground state and no long-range magnetic order down to at least $T=0.4$ K. Inelastic neutron scattering measurements show that the excitation spectrum consists of dispersive gapped singlet-triplet excitations, characteristic of spin-1/2 dimer-forming Heisenberg antiferromagnets. We identify a distinct two-dimensional dimerized coupling scheme with strong interdimer coupling ${J}^{\ensuremath{'}}/{J}_{1}\ensuremath{\approx}0.3$ that places malachite between strongly coupled alternating chains, square lattice antiferromagnets, and infinite-legged ladders. The geometry of the interaction scheme resembles the staggered dimer lattice, which may allow unconventional quantum criticality.}, number={6}, journal={PHYSICAL REVIEW B}, author={Canevet, E. and Fak, B. and Kremer, R. K. and Chun, J. H. and Enderle, M. and Gordon, E. E. and Bettis, J. L. and Whangbo, M. -H. and Taylor, J. W. and Adroja, D. T.}, year={2015}, month={Feb} } @article{wang_huang_li_lou_wang_dai_whangbo_2015, title={Synthesis and characterization of ZnS with controlled amount of S vacancies for photocatalytic H-2 production under visible light}, volume={5}, journal={Scientific Reports}, author={Wang, G. and Huang, B. B. and Li, Z. J. and Lou, Z. Z. and Wang, Z. Y. and Dai, Y. and Whangbo, M. H.}, year={2015} } @article{read_gordon_smith_yeon_morrison_whangbo_loye_2015, title={Synthesis of the Layered Quaternary Uranium-Containing Oxide Cs2Mn3U6O22 and Characterization of its Magnetic Properties}, volume={54}, ISSN={["1520-510X"]}, DOI={10.1021/acs.inorgchem.5b00552}, abstractNote={A layered quaternary uranium-containing oxide, Cs2Mn3U6O22, was crystallized from a cesium chloride flux. The crystal structure was determined to consist of α-U3O8 topological layers that are separated by alternating cesium and manganese layers. This ordered arrangement creates a separation between manganese layers of 13 Å, leading to complex low-dimensional magnetic properties. The compound crystallizes in a new structure type in the monoclinic space group, C2/m, with a = 6.8730(10) Å, b = 11.7717(17) Å, c = 13.374(2) Å, and β = 99.673(5)°. The magnetic properties were measured and analyzed by first-principles density functional theory calculations.}, number={11}, journal={INORGANIC CHEMISTRY}, author={Read, Cory M. and Gordon, Elijah E. and Smith, Mark D. and Yeon, Jeongho and Morrison, Gregory and Whangbo, Myung-Hwan and Loye, Hans-Conrad}, year={2015}, month={Jun}, pages={5495–5503} } @article{whangbo_gordon_bettis_bussmann-holder_koehler_2015, title={Tolerance Factor and Cation-Anion Orbital Interactions Differentiating the Polar and Antiferrodistortive Structures of Perovskite Oxides ABO(3)}, volume={641}, ISSN={["1521-3749"]}, DOI={10.1002/zaac.201500058}, abstractNote={Abstract We explored under what conditions perovskite oxides ABO 3 adopt a polar or an antiferrodistortive structure from the viewpoint of the tolerance factor τ and the orbital interactions of the empty orbitals of the A and B cations with the filled orbitals of their surrounding O 2– ions. Polar structures require the presence of a substantial size‐mismatch as well as strong cation‐anion orbital interactions at A or B cation sites. A tetragonal polar structure is preferred when the A cation empty orbitals are extended or when the B‐cation empty orbitals are contracted. A trigonal polar structure is favored in opposite cases. An antiferrodistortive structure is found for perovskites with weak size‐mismatch or those with substantial size‐mismatch if both A and B cations do not generate strong cation‐anion orbital interactions. Antiferrodistortive structures result from interactions involving the A cations with the O 4 squares of the face‐sharing A O 8 square‐prisms in a two‐in‐two‐out manner, and are found only when the A/O cation‐anion interactions are substantial.}, number={6}, journal={ZEITSCHRIFT FUR ANORGANISCHE UND ALLGEMEINE CHEMIE}, author={Whangbo, Myung-Hwan and Gordon, Elijah E. and Bettis, Jerry L., Jr. and Bussmann-Holder, Annette and Koehler, Juergen}, year={2015}, month={May}, pages={1043–1052} } @article{bussmann-holder_koehler_whangbo_2015, title={Unexpected Precursor Effects to the Structural Phase Transition in EuTiO3}, volume={641}, ISSN={["1521-3749"]}, DOI={10.1002/zaac.201400596}, abstractNote={Abstract The dynamical properties of EuTiO 3 are investigated to gain insight into its precursor effects analogous to those observed in many other perovskite oxides. In spite of the fact that a competition between the long wave length transverse optic mode and the zone boundary acoustic mode is absent, which makes the mode‐mode coupling inessential, acoustic instabilities on limited spatial regions appear well above T S . This confirms the notion that dynamic forerunners are inherent and precede any phase transition in cubic perovskite oxides.}, number={2}, journal={ZEITSCHRIFT FUR ANORGANISCHE UND ALLGEMEINE CHEMIE}, author={Bussmann-Holder, Annette and Koehler, Juergen and Whangbo, Mike-H.}, year={2015}, month={Feb}, pages={180–183} } @article{lou_huang_wang_ma_zhang_zhang_qin_dai_whangbo_2014, title={Ag6Si2O7: a Silicate Photocatalyst for the Visible Region}, volume={26}, ISSN={["1520-5002"]}, DOI={10.1021/cm500657n}, abstractNote={ADVERTISEMENT RETURN TO ISSUEPREVCommunicationNEXTAg6Si2O7: a Silicate Photocatalyst for the Visible RegionZaizhu Lou†, Baibiao Huang*†, Zeyan Wang†, Xiangchao Ma‡, Rui Zhang†‡, Xiaoyang Zhang†, Xiaoyan Qin†, Ying Dai‡, and Myung-Hwan Whangbo§View Author Information‡ †State Key Laboratory of Crystal Materials and ‡School of Physics, Shandong University, Jinan 250100, P. R. China§ Department of Chemistry, North Carolina State University, Raleigh, North Carolina 27695-8204, United States*E-mail: [email protected]Cite this: Chem. Mater. 2014, 26, 13, 3873–3875Publication Date (Web):June 12, 2014Publication History Received24 February 2014Revised10 June 2014Published online16 June 2014Published inissue 8 July 2014https://pubs.acs.org/doi/10.1021/cm500657nhttps://doi.org/10.1021/cm500657nrapid-communicationACS PublicationsCopyright © 2014 American Chemical SocietyRequest reuse permissionsArticle Views3090Altmetric-Citations130LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-AlertscloseSupporting Info (1)»Supporting Information Supporting Information SUBJECTS:Catalytic activity,Degradation,Electrical conductivity,Photocatalysis,Photocatalysts Get e-Alerts}, number={13}, journal={CHEMISTRY OF MATERIALS}, author={Lou, Zaizhu and Huang, Baibiao and Wang, Zeyan and Ma, Xiangchao and Zhang, Rui and Zhang, Xiaoyang and Qin, Xiaoyan and Dai, Ying and Whangbo, Myung-Hwan}, year={2014}, month={Jul}, pages={3873–3875} } @article{lee_kang_hong_shim_whangbo_2014, title={Analysis of the Difference between the Pyroxenes LiFeSi2O6 and LiFeGe2O6 in Their Spin Order, Spin Orientation, and Ferrotoroidal Order}, volume={26}, ISSN={["1520-5002"]}, DOI={10.1021/cm5001413}, abstractNote={The pyroxenes LiFeSi2O6 and LiFeGe2O6 are isostructural and isoelectronic, but they differ in their spin order, spin orientation and ferrotoroidal order. The reasons for these differences were probed by density functional theory electronic structure calculations and magnetic dipole–dipole (MDD) interaction energy calculations. The ferromagnetic Fe-zigzag chains of LiFeSi2O6 arise from the antiferromagnetic interchain spin exchanges and the antiferromagnetic Fe-zigzag chains of LiFeGe2O6 from the antiferromagnetic intrachain spin exchange. The preferred spin orientations of LiFeGe2O6 and LiFeSi2O6 are not caused by spin–orbit coupling but by MDD interactions. LiFeSi2O6 undergoes a ferrotoroidal order because it has spin exchange rings made up of an even number of antiferromagnetic spin exchanges paths with comparable strengths. A ferrotoroidal order is not expected for LiFeGe2O6 because it has no such spin exchange rings.}, number={4}, journal={CHEMISTRY OF MATERIALS}, author={Lee, Changhoon and Kang, Jinhee and Hong, Jisook and Shim, Ji Hoon and Whangbo, Myung-Hwan}, year={2014}, month={Feb}, pages={1745–1750} } @article{caslin_kremer_razavi_schulz_munoz_pertlik_liu_whangbo_law_2014, title={Characterization of the spin-1/2 linear-chain ferromagnet CuAs2O4}, volume={89}, ISSN={["2469-9969"]}, DOI={10.1103/physrevb.89.014412}, abstractNote={The magnetic and lattice properties of the $S$=1/2 quantum-spin-chain ferromagnet, CuAs$_2$O$_4$, mineral name trippkeite, were investigated. The crystal structure of CuAs$_2$O$_4$ is characterized by the presence of corrugated CuO$_2$ ribbon chains. Measurements of the magnetic susceptibility, heat capacity, electron paramagnetic resonance and Raman spectroscopy were performed. Our experiments conclusively show that a ferromagnetic transition occurs at $\sim$7.4 K. $\textit{Ab initio}$ DFT calculations reveal dominant ferromagnetic nearest-neighbor and weaker antiferromagnetic next- nearest-neighbor spin exchange interactions along the ribbon chains. The ratio of $J_{\rm nn}$/$J_{\rm nnn}$ is near -4, placing CuAs$_2$O$_4$ in close proximity to a quantum critical point in the $J_{\rm nn}$ - $J_{\rm nnn}$ phase diagram. TMRG simulations used to analyze the magnetic susceptibility confirm this ratio. Single-crystal magnetization measurements indicate that a magnetic anisotropy forces the Cu$^{2+}$ spins to lie in an easy plane perpendicular to the $c$-axis. An analysis of the field and temperature dependent magnetization by modified Arrott plots reveals a 3d-XY critical behavior. Lattice perturbations induced by quasi-hydrostatic pressure and temperature were mapped via magnetization and Raman spectroscopy.}, number={1}, journal={PHYSICAL REVIEW B}, author={Caslin, K. and Kremer, R. K. and Razavi, F. S. and Schulz, A. and Munoz, A. and Pertlik, F. and Liu, J. and Whangbo, M. -H. and Law, J. M.}, year={2014}, month={Jan} } @article{hu_johnsson_law_bettis_whangbo_kremer_2014, title={Crystal Structure and Magnetic Properties of FeSeO3F-Alternating Antiferromagnetic S=5/2 chains}, volume={53}, ISSN={["1520-510X"]}, DOI={10.1021/ic5003995}, abstractNote={The new oxofluoride FeSeO3F, which is isostructural with FeTeO3F and GaTeO3F, was prepared by hydrothermal synthesis, and its structure was determined by X-ray diffraction. The magnetic properties of FeSeO3F were characterized by magnetic susceptibility and specific heat measurements, by evaluating its spin exchanges on the basis of density functional theory (DFT) calculations, and by performing a quantum Monte Carlo simulation of the magnetic susceptibility. FeSeO3F crystallizes in the monoclinic space group P21/n and has one unique Se4+ ion and one unique Fe3+ ion. The building blocks of FeSeO3F are [SeO3] trigonal pyramids and cis-[FeO4F2] distorted octahedra. The cis-[FeO4F2] octahedra are condensed by sharing the O–O and F–F edges alternatingly to form [FeO3F]∞ chains, which are interconnected via the [SeO3] pyramids by corner-sharing. The magnetic susceptibility of FeSeO3F is characterized by a broad maximum at 75(2) K and a long-range antiferromagnetic order below ∼45 K. The latter is observed by magnetic susceptibility and specific heat measurements. DFT calculations show that the Fe–F–Fe spin exchange is stronger than the Fe–O–Fe exchange, so each [FeO3F]∞ chain is a Heisenberg antiferromagnetic chain with alternating antiferromagnetic spin exchanges. The temperature dependence of the magnetic susceptibility is well-reproduced by a quantum-Monte Carlo simulation.}, number={8}, journal={INORGANIC CHEMISTRY}, author={Hu, Shichao and Johnsson, Mats and Law, Joseph M. and Bettis, Jerry L., Jr. and Whangbo, Myung-Hwan and Kremer, Reinhard K.}, year={2014}, month={Apr}, pages={4250–4256} } @article{koo_whangbo_2014, title={Density functional investigation of why Ba2BiFeS5 and Ba2SbFeS5 differ in their magnetic properties}, volume={360}, ISSN={["1873-4766"]}, DOI={10.1016/j.jmmm.2014.02.024}, abstractNote={We examined the cause for the difference in the magnetic properties of the isostructural/isoelectronic compounds Ba2SbFeS5 and Ba2BiFeS5 by evaluating their spin exchange parameters on the basis of density functional theory calculations. The difference is traced to the exchange triangle made up of three strongly antiferromagnetic spin exchange paths, which exhibits stronger spin frustration for Ba2SbFeS5 than for Ba2BiFeS5.}, journal={JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS}, author={Koo, Hyun-Joo and Whangbo, Myung-Hwan}, year={2014}, month={Jun}, pages={152–156} } @article{ma_dai_yu_lou_huang_whangbo_2014, title={Electron Hole Pair Generation of the Visible-Light Plasmonic Photocatalyst Ag@AgCl: Enhanced Optical Transitions Involving Midgap Defect States of AgCl}, volume={118}, ISSN={["1932-7455"]}, DOI={10.1021/jp5023604}, abstractNote={We explored how the visible-light energy absorbed by noble-metal nanoparticles (NPs) is converted to electrons and holes in the semiconductor in a visible-light plasmonic photocatalyst by studying the representative system Ag@AgCl on the basis of density functional calculations and classical electrodynamics calculations. These calculations suggest that the energy transfer from the Ag NPs to the semiconductor AgCl requires the presence of midgap defect states in the semiconductor and that the surface plasmon resonance (SPR) of the Ag NPs strongly enhances the optical transitions of the semiconductor involving the defect states. We verified this suggestion experimentally by preparing Ag@AgCl samples possessing different degrees of bulk and surface defects and subsequently by carrying out photodegradation experiments using these samples.}, number={23}, journal={JOURNAL OF PHYSICAL CHEMISTRY C}, author={Ma, Xiangchao and Dai, Ying and Yu, Lin and Lou, Zaizhu and Huang, Baibiao and Whangbo, Myung-Hwan}, year={2014}, month={Jun}, pages={12133–12140} } @article{lee_lee_lee_whangbo_2014, title={Evaluating the Curie-Weiss Temperature of a Magnetic System Composed of Nonequivalent Magnetic Ions in Terms of Spin Exchange Constants}, volume={35}, ISSN={["1229-5949"]}, DOI={10.5012/bkcs.2014.35.5.1277}, abstractNote={E-mail: mike_whangbo@ncsu.eduReceived January 18, 2014, Accepted February 5, 2014Key Words : Nonequivalent magnetic ions, Curie-Weiss temperature, Mean field theory, Spin exchange pa-rameters, Density functional theory Magnetic properties of a system containing magnetic ionsare related to its electronic structure,}, number={5}, journal={BULLETIN OF THE KOREAN CHEMICAL SOCIETY}, author={Lee, Kee Hag and Lee, Ji Young and Lee, Changhoon and Whangbo, Myung-Hwan}, year={2014}, month={May}, pages={1277–1278} } @article{mccabe_stock_bettis_whangbo_evans_2014, title={Magnetism of the Fe2+ and Ce3+ sublattices in Ce2O2FeSe2: A combined neutron powder diffraction, inelastic neutron scattering, and density functional study}, volume={90}, ISSN={["2469-9969"]}, DOI={10.1103/physrevb.90.235115}, abstractNote={The discovery of superconductivity in the 122 iron selenide materials above 30 K necessitates an understanding of the underlying magnetic interactions. We present a combined experimental and theoretical investigation of magnetic and semiconducting Ce$_{2}$O$_{2}$FeSe$_{2}$ composed of chains of edge-linked iron selenide tetrahedra. The combined neutron diffraction and inelastic scattering study and density functional calculations confirm the ferromagnetic nature of nearest-neighbour Fe -- Se -- Fe interactions in the ZrCuSiAs-related iron oxyselenide Ce$_{2}$O$_{2}$FeSe$_{2}$. Inelastic measurements provide an estimate of the strength of nearest-neighbor Fe -- Fe and Fe -- Ce interactions. These are consistent with density functional theory calculations, which reveal that correlations in the Fe--Se sheets of Ce$_{2}$O$_{2}$FeSe$_{2}$ are weak. The Fe on-site repulsion $U_{Fe}$ is comparable to that reported for oxyarsenides and K$_{1-x}$Fe$_{2-y}$Se$_{2}$, which are parents to iron-based superconductors.}, number={23}, journal={PHYSICAL REVIEW B}, author={McCabe, E. E. and Stock, C. and Bettis, J. L., Jr. and Whangbo, M. -H. and Evans, J. S. O.}, year={2014}, month={Dec} } @article{liu_koo_xiang_kremer_whangbo_2014, title={Most spin-1/2 transition-metal ions do have single ion anisotropy}, volume={141}, number={12}, journal={Journal of Chemical Physics}, author={Liu, J. and Koo, H. J. and Xiang, H. J. and Kremer, R. K. and Whangbo, M. H.}, year={2014} } @article{koo_whangbo_2014, title={Spin Exchange and Magnetic Dipole Dipole Interactions Leading to the Magnetic Superstructures of MAs2O6 (M = Mn, Co, Ni)}, volume={53}, ISSN={["1520-510X"]}, DOI={10.1021/ic500156e}, abstractNote={The three isostructural magnetic oxides MAs2O6 (M = Mn, Co, Ni) containing high-spin M(2+) ions undergo a long-range antiferromagnetic ordering below 30 K, but their ordered magnetic structures are not identical. While CoAs2O6 and NiAs2O6 adopt the commensurate superstructure of q1 = (0, 0, 1/2), MnAs2O6 has the incommensurate superstructure of q2 = (0.055, 0.389, 0.136). The cause for this difference was examined by calculating their spin exchange and magnetic dipole-dipole interaction energies. In CoAs2O6 and NiAs2O6, the strongest M-O···O-M spin exchange, J1, dominates over other exchanges, hence leading to the q1 superstructure. For MnAs2O6, the spin exchanges are not a deciding factor leading to its magnetic superstructure, being all weak and comparable in strengths, but the magnetic dipole-dipole interactions are.}, number={7}, journal={INORGANIC CHEMISTRY}, author={Koo, Hyun-Joo and Whangbo, Myung-Hwan}, year={2014}, month={Apr}, pages={3812–3817} } @article{ma_dai_wei_huang_whangbo_2014, title={Strain-induced quantum spin Hall effect in methyl-substituted germanane GeCH3}, volume={4}, journal={Scientific Reports}, author={Ma, Y. D. and Dai, Y. and Wei, W. and Huang, B. B. and Whangbo, M. H.}, year={2014} } @article{law_koo_whangbo_bruecher_pomjakushin_kremer_2014, title={Strongly correlated one-dimensional magnetic behavior of NiTa2O6}, volume={89}, ISSN={["2469-9969"]}, DOI={10.1103/physrevb.89.014423}, abstractNote={The magnetic properties of NiTa${}_{2}$O${}_{6}$ were investigated by magnetic susceptibility, specific heat, electron paramagnetic resonance, neutron powder diffraction, and pulse field magnetization measurements. Accompanying ab initio DFT calculations of the spin-exchange constants complemented and supported our experimental findings that NiTa${}_{2}$O${}_{6}$ must be described as a quasi-1D Heisenberg $S=1$ spin chain system with a nearest-neighbor only antiferromagnetic spin-exchange interaction of 18.92(2) K. Interchain coupling is by about two orders of magnitude smaller. Electron paramagnetic resonance measurements on Mg${}_{1\ensuremath{-}x}$Ni${}_{x}$Ta${}_{2}$O${}_{6}$ ($x\ensuremath{\approx}1%$) polycrystalline samples enabled us to estimate the single-ion zero-field splitting of the $S=1$ states which amounts to less than 4% of the nearest-neighbor spin-exchange interaction. At 0 T NiTa${}_{2}$O${}_{6}$ undergoes long-range antiferromagnetic ordering at 10.3(1) K evidenced by a $\ensuremath{\lambda}$-type anomaly in the specific heat capacity. On application of a magnetic field the specific heat anomaly is smeared out. We confirmed the magnetic structure by neutron powder diffraction measurements and at 2.00(1) K refined a magnetic moment of 1.93(5) ${\ensuremath{\mu}}_{\mathrm{B}}$ per Ni${}^{2+}$ ion. Additionally, we followed the magnetic order parameter as a function of temperature. Last, we found saturation of the magnetic moment at 55.5(5) T with a $g$ factor of 2.14(1), with an additional high field phase above 12.8(1) T. The onset of the new high field phase is not greatly affected by temperature, but rather smears out as one approaches the long-range ordering temperature.}, number={1}, journal={PHYSICAL REVIEW B}, author={Law, J. M. and Koo, H. -J. and Whangbo, M. -H. and Bruecher, E. and Pomjakushin, V. and Kremer, R. K.}, year={2014}, month={Jan} } @article{stroppa_di sante_barone_bokdam_kresse_franchini_whangbo_picozzi_2014, title={Tunable ferroelectric polarization and its interplay with spin-orbit coupling in tin iodide perovskites}, volume={5}, journal={Nature Communications}, author={Stroppa, A. and Di Sante, D. and Barone, P. and Bokdam, M. and Kresse, G. and Franchini, C. and Whangbo, M. H. and Picozzi, S.}, year={2014} } @article{david_kabbour_pautrat_touati_whangbo_mentre_2014, title={Two-Orbital Three-Electron Stabilizing Interaction for Direct Co2+ - As3+ Bonds involving Square-Planar CoO4 in BaCoAs2O5}, volume={53}, ISSN={["1521-3773"]}, DOI={10.1002/anie.201311183}, abstractNote={Abstract The quest for new oxides with cations containing active lone‐pair electrons ( E ) covers a broad field of targeted specificities owing to asymmetric electronic distribution and their particular band structure. Herein, we show that the novel compound BaCoAs 2 O 5 , with lone‐pair As 3+ ions, is built from rare square‐planar Co 2+ O 4 involved in direct bonding between As 3+ E and Co 2+ d z 2 orbitals (CoAs=2.51 Å). By means of DFT and Hückel calculations, we show that this σ‐type overlapping is stabilized by a two‐orbital three‐electron interaction allowed by the high‐spin character of the Co 2+ ions. The negligible experimental spin‐orbit coupling is expected from the resulting molecular orbital scheme in O 3 As E –CoO 4 clusters.}, number={12}, journal={ANGEWANDTE CHEMIE-INTERNATIONAL EDITION}, author={David, Renald and Kabbour, Houria and Pautrat, Alain and Touati, Nadia and Whangbo, Myung-Hwan and Mentre, Olivier}, year={2014}, month={Mar}, pages={3111–3114} } @article{bao_ma_chen_xu_enriquez_chen_zhang_bettis_whangbo_dong_et al._2014, title={Ultrafast atomic layer-by-layer oxygen vacancy-exchange diffusion in double-perovskite LnBaCo(2)O(5.5+delta) thin films}, volume={4}, journal={Scientific Reports}, author={Bao, S. Y. and Ma, C. R. and Chen, G. and Xu, X. and Enriquez, E. and Chen, C. L. and Zhang, Y. M. and Bettis, J. L. and Whangbo, M. H. and Dong, C. and et al.}, year={2014} } @article{wang_bao_liu_collins_ma_liu_chen_dong_whangbo_guo_et al._2014, title={Ultrafast chemical dynamic behavior in highly epitaxial LaBaCo2O5+delta thin films}, volume={2}, ISSN={["2050-7534"]}, DOI={10.1039/c4tc00492b}, abstractNote={The redox reactions of highly epitaxial LaBaCo2O5+δ (LBCO) thin films exposed to the switching flow of reducing (H2) and oxidizing (O2) gases were examined at various temperatures between 260 and 700 °C. Their electrical resistance was measured using a precise ac bridge measurement system.}, number={28}, journal={JOURNAL OF MATERIALS CHEMISTRY C}, author={Wang, H. B. and Bao, S. Y. and Liu, J. and Collins, G. and Ma, C. R. and Liu, M. and Chen, C. L. and Dong, C. and Whangbo, M. -H. and Guo, H. M. and et al.}, year={2014}, pages={5660–5666} } @article{kim_rhee_koo_kasapbasi_whangbo_2013, title={A Contoured Network of Anionic Trimesic Acids on Au(111) and Its Host-Guest Chemistry}, volume={117}, ISSN={["1932-7455"]}, DOI={10.1021/jp403203s}, abstractNote={This work describes a trimesic acid (TMA) network formed at the open-circuit potential (OCP, ∼0.13 V) on Au(111), which we investigate with electrochemical scanning tunneling microscopy (STM). The unit cell of the TMA network at the OCP was (5√3 × 5√3)R30°–4TMA, while that of a well-known honeycomb network of flat-lying TMAs at −0.1 V was (6 × 6)R30°–2TMA. The most significant difference between the two networks is the fraction of hydrogen bonds appearing as bright spots in the STM images: it is 1/3 in the former but 1 in the latter. Additional differences were the shapes and lengths of the STM spots and the packing density of TMAs. A contoured network composed of crownlike anionic TMA hexamers was proposed to explain all the differences. The TMAs in the crownlike hexamer were rotated along the molecular axis and were tilted up from the surface by ∼30° to have hydrogen bonds with reasonable O–H···O distance, and the hexamers were interconnected to a contoured network. The existence of the anionic TMA hexamer was evidenced by selective host–guest interaction of Cu2+ ions and 1-mercaptohexane with the contoured network. At a higher potential than the OCP, simple arrays of anionic TMA dimers with much higher packing densities were observed, depending on the availability of TMAs from solution. The potential dependence of the structure of the TMA adlayer is discussed in terms of a transition from molecular adsorption to anionic adsorption.}, number={44}, journal={JOURNAL OF PHYSICAL CHEMISTRY C}, author={Kim, Jandee and Rhee, Choong K. and Koo, Hyun-J. and Kasapbasi, Emine E. and Whangbo, Myung-H.}, year={2013}, month={Nov}, pages={22636–22643} } @article{jin_kim_jo_bettis_koo_whangbo_hwang_2013, title={A Crucial Role of Bond Covalency Competition in Determining the Bandgap and Photocatalytic Performance of Silver Oxosalts}, volume={117}, ISSN={["1932-7455"]}, DOI={10.1021/jp4101784}, abstractNote={The optical bandgaps, the surface charges, and the photocatalytic activities of the silver oxosalts Ag3AsO4, Ag2CO3, Ag3PO4, Ag2SO4, and Ag2SeO4 are systematically investigated with several experimental techniques and first principles density functional theory calculations. The trends in the optical bandgaps and the surface charges of these silver oxosalts, Agx(XOy)z, are analyzed by considering how the X–O bond covalency affects the charge on the terminal oxygen atoms and the Ag–O bond covalency. The optical bandgaps of Agx(XOy)z are well-described by the bond-covalency competition in the Ag–O–X linkages because an increase in the overlap between the O 2s/2p and X ns/np orbitals decreases the overlap between the Ag 4d and O 2s/2p orbitals. The optical bandgap increases linearly with increasing the Z/r ratio of the atom X, a simple measure of the X–O bond covalency. In the photodegradation of charged molecules, the surface charge of Agx(XOy)z plays a prominent role and decreases with increasing the Z/r ratio. As expected from the present theoretical predictions, newly investigated Ag2SeO4 exhibits a promising photocatalytic activity under visible light. The Z/r ratio of the central atom X provides an effective measure for predicting the photocatalyst performance and the optical bandgap of silver oxosalts Agx(XOy)z.}, number={50}, journal={JOURNAL OF PHYSICAL CHEMISTRY C}, author={Jin, Xiaoyan and Kim, In Young and Jo, Yun Kyung and Bettis, Jerry L., Jr. and Koo, Hyun-Joo and Whangbo, Myung-Hwan and Hwang, Seong-Ju}, year={2013}, month={Dec}, pages={26509–26516} } @article{david_pautrat_filimonov_kabbour_vezin_whangbo_mentre_2013, title={Across the Structural Re-Entrant Transition in BaFe2(PO4)(2): Influence of the Two-Dimensional Ferromagnetism}, volume={135}, ISSN={["0002-7863"]}, DOI={10.1021/ja404697b}, abstractNote={BaFe2(PO4)2 was recently prepared by hydrothermal synthesis and identified as the first two-dimensional (2D) Ising ferromagnetic oxide, in which honeycomb layers made up of edge-sharing FeO6 octahedra containing high-spin Fe(2+) ions (S = 2) are isolated by PO4 groups and Ba(2+) cations. BaFe2(PO4)2 has a trigonal R-3 structure at room temperature but adopts a triclinic P-1 structure below 140 K due to the Jahn-Teller (JT) instability arising from the (t2g)(4)(eg)(2) configuration. The triclinic crystal structure was refined to find significantly distorted Fe(2+)O6 octahedra in the honeycomb layers while the distortion amplitude QJT was estimated to 0.019 Å. The JT stabilization energy is estimated to be ∼7 meV per formula unit by DFT calculations. Below ∼70 K, very close to the ferromagnetic transition temperature Tc = 65.5 K, the structure of BaFe2(PO4)2 returns to a trigonal R-3 structure in the presence of significant ferromagnetic domains. This rare re-entrant structural transition is accompanied by a discontinuous change in the quadrupolar splitting of Fe(2+), as determined by Mössbauer spectroscopy. EPR measurements show the presence of magnetic domains well above Tc , as expected for a ferromagnetic 2D Ising system, and support that the magnetism of BaFe2(PO4)2 is uniaxial (g⊥ = 0).}, number={35}, journal={JOURNAL OF THE AMERICAN CHEMICAL SOCIETY}, author={David, Renald and Pautrat, Alain and Filimonov, Dmitry and Kabbour, Houria and Vezin, Herve and Whangbo, Myung-Hwan and Mentre, Olivier}, year={2013}, month={Sep}, pages={13023–13029} } @article{lapidus_manson_park_clement_ghannadzadeh_goddard_lancaster_moeller_blundell_telling_et al._2013, title={Antiferromagnetic ordering through a hydrogen-bonded network in the molecular solid CuF2(H2O)(2)(3-chloropyridine)}, volume={49}, ISSN={["1359-7345"]}, DOI={10.1039/c2cc37444g}, abstractNote={CuF(2)(H(2)O)(2)(3-chloropyridine) possesses a five-coordinate Cu(2+) center with a slightly distorted trigonal bypyramidal coordination geometry. Strong intermolecular F···H-O hydrogen bonds enable the formation of 2D layers and provide the primary magnetic exchange path that leads to the stabilization of long-range antiferromagnetic (AFM) order below T(N) = 2.1 K.}, number={5}, journal={CHEMICAL COMMUNICATIONS}, author={Lapidus, Saul H. and Manson, Jamie L. and Park, Hyunsoo and Clement, Alexander J. and Ghannadzadeh, Saman and Goddard, Paul and Lancaster, Tom and Moeller, Johannes S. and Blundell, Stephen J. and Telling, Mark T. F. and et al.}, year={2013}, pages={499–501} } @article{wang_huang_ma_wang_qin_zhang_dai_whangbo_2013, title={Cu2(OH)PO4, a Near-Infrared-Activated Photocatalyst}, volume={52}, ISSN={["1521-3773"]}, DOI={10.1002/anie.201301306}, abstractNote={Crystal power! Libethenite, Cu2(OH)PO4 (see 4–5 μm×1.5 μm image), absorbs strongly in the near-infrared (NIR) region and is an effective photocatalyst for the decomposition of 2,4-dichlorophenol in aqueous solution under NIR irradiation. This NIR activation of the photocatalyst is due to a facile transfer of photogenerated electrons from the trigonal bipyramidal CuII sites to the adjacent octahedral CuII sites.}, number={18}, journal={ANGEWANDTE CHEMIE-INTERNATIONAL EDITION}, author={Wang, Gang and Huang, Baibiao and Ma, Xiangchao and Wang, Zeyan and Qin, Xiaoyan and Zhang, Xiaoyang and Dai, Ying and Whangbo, Myung-Hwan}, year={2013}, pages={4810–4813} } @article{wang_jain_choi_tol_cheetham_kroto_koo_zhou_hwang_choi_et al._2013, title={Dimethylammonium copper formate [(CH3)(2)NH2]Cu(HCOO)(3): A metal-organic framework with quasi-one-dimensional antiferromagnetism and magnetostriction}, volume={87}, ISSN={["1550-235X"]}, DOI={10.1103/physrevb.87.224406}, abstractNote={Metal-organic frameworks (MOFs) can exhibit many interesting properties such as multiferroic behavior, dipolar glass, gas storage, and protonic conductivity. Here we report that dimethylammonium copper formate (DMACuF) [(CH${}_{3}$)${}_{2}$NH${}_{2}$]Cu(HCOO)${}_{3}$, a cation templated nonporous MOF with perovskite topology, exhibits strong one-dimensional (1D) antiferromagnetism with a N\'eel temperature, ${T}_{N}$, of 5.2 K. These conclusions are derived from detailed magnetic susceptibility, heat capacity, dielectric constant, and high-frequency electron paramagnetic resonance measurements as well as density functional theory (DFT) calculations. The magnetic susceptibility exhibits a broad maximum at \ensuremath{\sim}50 K, suggesting low-dimensional magnetism; heat capacity measurements show a N\'eel temperature of 5.2 K. The magnetization versus field data at 1.8 K shows a spin-flop transition at ${H}_{sf}$ \ensuremath{\sim} 1.7 T. The ratio ${T}_{N}$/$J=6.5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}2}$, where $J$ is the near-neighbor exchange constant (77.4 K), and the small value (2 K) of the interchain coupling suggests that DMACuF is close to an ideal 1D magnet. In this three-dimensional crystal lattice, the 1D magnetic behavior is made possible by the Jahn-Teller distortion of the 3${d}^{9}$ Cu${}^{2+}$ ions. Temperature dependence of the electron paramagnetic resonance field and the linewidth exhibits critical broadening for temperatures below 50 K, following a behavior quite characteristic of 1D spin systems. DFT calculations show that [(CH${}_{3}$)${}_{2}$NH${}_{2}$]Cu(HCOO)${}_{3}$ has a magnetic structure in which 1D antiferromagnetic chains parallel to the $c$ direction are weakly coupled ferromagnetically, supporting the thermomagnetic and EPR results. Dielectric measurements under applied magnetic fields of 0\ensuremath{-}7 T reveal a kink at the ${T}_{N}$, a clear indication of magnetostriction behavior.}, number={22}, journal={PHYSICAL REVIEW B}, author={Wang, Zhenxing and Jain, Prashant and Choi, Kwang-Yong and Tol, Johan and Cheetham, Anthony K. and Kroto, Harold W. and Koo, Hyun-Joo and Zhou, Haidong and Hwang, Jungmin and Choi, Eun Sang and et al.}, year={2013}, month={Jun} } @article{wang_huang_ma_wang_qin_zhang_dai_whangbo_2013, title={Efficient Separation of Photogenerated Electron-Hole Pairs by the Combination of a Heterolayered Structure and Internal Polar Field in Pyroelectric BiOIO3 Nanoplates}, volume={19}, ISSN={["1521-3765"]}, DOI={10.1002/chem.201302884}, abstractNote={Electrify your chemistry! Pyroelectric heterolayered BiOIO3 nanoplates efficiently separate photogenerated electron-hole pairs due to the combined effect of their heterolayered structure and internal polar field (see scheme). Pyroelectric BiOIO3 nanoplates, synthesized by a simple hydrothermal method, were found to possess a superior photocatalytic activity under UV irradiation. As a service to our authors and readers, this journal provides supporting information supplied by the authors. Such materials are peer reviewed and may be re-organized for online delivery, but are not copy-edited or typeset. Technical support issues arising from supporting information (other than missing files) should be addressed to the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.}, number={44}, journal={CHEMISTRY-A EUROPEAN JOURNAL}, author={Wang, Wenjun and Huang, Baibiao and Ma, Xiangchao and Wang, Zeyan and Qin, Xiaoyan and Zhang, Xiaoyang and Dai, Ying and Whangbo, Myung-Hwan}, year={2013}, month={Oct}, pages={14777–14780} } @article{lee_hong_whangbo_shim_2013, title={Enhancing the Thermoelectric Properties of Layered Transition-Metal Dichalcogenides 2H-MQ(2) (M = Mo, W; Q = S, Se, Te) by Layer Mixing: Density Functional Investigation}, volume={25}, ISSN={["1520-5002"]}, DOI={10.1021/cm402281n}, abstractNote={We explored how to improve the thermoelectric properties of the layered transition-metal dichalcogenides 2H-MQ2 (M = Mo, W; Q = S, Se, Te) by comparing the thermoelectric properties of hypothetical mixed-layer systems 2H-MQ2/2H-MQ′2, in which two different layers 2H-MQ2 and 2H-MQ′2 (Q, Q′ = S, Se, Te) alternate, with those of their pure components on the basis of density functional calculations. Our study predicts that the mixed-layer compounds MS2/MTe2 (M = Mo, W) strongly enhance the thermoelectric properties as a consequence of reducing the band gap and the interlayer van der Waals interactions. The layer-mixing is predicted to be a promising way of improving the thermoelectric properties of 2H-MQ2.}, number={18}, journal={CHEMISTRY OF MATERIALS}, author={Lee, Changhoon and Hong, Jisook and Whangbo, Myung-Hwan and Shim, Ji Hoon}, year={2013}, month={Sep}, pages={3745–3752} } @article{jeong_kim_cha_son_park_kim_cho_whangbo_yoo_kim_2013, title={Hydrogen Sensing under Ambient Conditions Using SnO2 Nanowires: Synergetic Effect of Pd/Sn Codeposition}, volume={13}, ISSN={["1530-6992"]}, DOI={10.1021/nl402998g}, abstractNote={Semiconducting SnO2 nanowires deposited with Pd and Sn nanoparticles on their surface are shown to be a highly sensitive hydrogen sensor with fast response time at room temperature. Compared with the SnO2 nanowire deposited with Pd or Sn nanoparticles alone, the Pd/Sn-deposited SnO2 nanowire exhibits a significant improvement in the sensitivity and reversibility of sensing hydrogen gas in the air at room temperature. Our investigation indicates that two factors are responsible for the synergistic effect of Pd/Sn codeposition on SnO2 nanowires. One is that in the presence of Pd the oxidation of Sn nanoparticles on the surface of the SnO2 nanowire is incomplete leading only to suboxides SnOx (1 ≤ x < 2), and the other is that the surface of the Pd/Sn-deposited SnO2 nanowire is almost perfectly hydrophobic.}, number={12}, journal={NANO LETTERS}, author={Jeong, Seung Ho and Kim, Sol and Cha, Junho and Son, Min Soo and Park, Sang Han and Kim, Ha-Yeong and Cho, Man Ho and Whangbo, Myung-Hwan and Yoo, Kyung-Hwa and Kim, Sung-Jin}, year={2013}, month={Dec}, pages={5938–5943} } @article{lou_huang_wang_qin_zhang_liu_zhang_dai_whangbo_2013, title={Interface kinetic diffusion reaction leading to fast and continuous generation of AgCl nanocubes in NaCl solution}, volume={42}, number={42}, journal={Dalton Transactions (Cambridge, England : 2003)}, author={Lou, Z. Z. and Huang, B. B. and Wang, Z. Y. and Qin, X. Y. and Zhang, X. Y. and Liu, Y. Y. and Zhang, R. and Dai, Y. and Whangbo, M. H.}, year={2013}, pages={15219–15225} } @article{nenert_koo_colin_bauer_bellitto_ritter_righini_whangbo_2013, title={Magnetic Order Through Super-Superexchanges in the Polar Magnetoelectric Organic-Inorganic Hybrid Cr[(D3N-(CH2)(2)-PO3)(Cl)(D2O)]}, volume={52}, ISSN={["1520-510X"]}, DOI={10.1021/ic301874v}, abstractNote={The crystal and magnetic structures of the organic-inorganic hybrid compound Cr(II) ammoniumethylphosphonate chloride monohydrate, Cr[D(3)N-(CH(2))(2)-PO(3))(Cl)(D(2)O)] (1), have been studied by temperature-dependent neutron powder diffraction and superconducting quantum interference device (SQUID) magnetometry. The compound represents a rare example of a magnetoelectric polar organic-inorganic hybrid solid, containing high spin Cr(2+) ions (S = 2) and is a canted antiferromagnet (weak ferromagnet) below T(N) = 5.5 K. The neutron powder diffraction pattern recorded at T = 10 K, shows that the partially deuterated compound crystallizes in the same non centrosymmetric monoclinic space group P2(1) (No. 4) with the following unit-cell parameters: a = 5.24041(4) Å, b =13.93113(8) Å, c = 5.26081(4) Å, and β = 105.4347(5)°. Powder neutron diffraction of a partially deuterated sample has enabled us, for the first time, to locate the water molecule. At low temperature, the compound presents a canted antiferromagnetic state characterized by k = 0 resulting in the magnetic symmetry P2(1)'. This symmetry is in agreement with the previously reported large magnetodielectric effect. The crystal structure of (1) can be described as being built up of triangular lattice planes made up of [Cr(II)O(4)Cl] square pyramids which are separated by ammonium ethyl groups along the b axis. The transition from paramagnetic to weakly ferromagnetic state results from super-superexchanges only. Surprisingly, while the overall magnetic behavior is antiferromagnetic, the Cr(II)O(4)Cl planes are ferromagnetic, and the strongest antiferromagnetic coupling is via the ammonium ethyl groups. Our density functional calculations confirm these aspects of the spin exchange interactions of (1) and that the spin exchange interactions between Cr(II) ions are considerably weak compared with the single-ion anisotropy of Cr(II).}, number={2}, journal={INORGANIC CHEMISTRY}, author={Nenert, Gwilherm and Koo, Hyun-Joo and Colin, Claire V. and Bauer, Elvira M. and Bellitto, Carlo and Ritter, Clemens and Righini, Guido and Whangbo, Myung-Hwan}, year={2013}, month={Jan}, pages={753–760} } @article{nenert_bettis_kremer_ben yahia_ritter_gaudin_isnard_whangbo_2013, title={Magnetic Properties of the RbMnPO4 Zeolite-ABW-Type Material: A Frustrated Zigzag Spin Chain}, volume={52}, ISSN={["1520-510X"]}, DOI={10.1021/ic401408f}, abstractNote={The crystal structure and magnetic properties of the RbMnPO4 zeolite-ABW type material have been studied by temperature-dependent neutron powder diffraction, low temperature magnetometry and heat capacity measurements. RbMnPO4 represents a rare example of a weak ferromagnetic polar material, containing Mn2+ ions with TN = 4.7 K. The neutron powder diffraction pattern recorded at T = 10 K shows that the compound crystallizes in the chiral and polar monoclinic space group P21 (No. 4) with the unit-cell parameters: a = 8.94635(9) {\AA}, b = 5.43415(5) {\AA}, c = 9.10250(8) {\AA} and beta = 90.4209(6){\deg}. A close inspection of the crystal structure of RbMnPO4 shows that this material presents two different types of zigzag chains running along the b axis. This is a unique feature among the zeolite-ABW type materials exhibiting the P21 symmetry. At low temperature, RbMnPO4 exhibits a canted antiferromagnetic structure characterized by the propagation vector k1 = 0 resulting in the magnetic symmetry P21. The magnetic moments lie mostly along the b axis with the ferromagnetic component being in the ac plane. Due to the geometrical frustration present in this system, an intermediate phase appears within the temperature range 4.7 - 5.1 K characterized by the propagation vector k2 = (kx, 0, kz) with kx/kz = 2. This ratio is reminiscent of the multiferroic phase of the orthorhombic RMnO3 phases (R = rare earth). This suggests that RbMnPO4 could present some multiferroic properties at low temperature. Our density functional calculations confirm the presence of magnetic frustration, which explains this intermediate incommensurate phase. Taking into account the strongest magnetic interactions, we are able to reproduce the magnetic structure observed experimentally at low temperature.}, number={16}, journal={INORGANIC CHEMISTRY}, author={Nenert, Gwilherm and Bettis, Jerry, Jr. and Kremer, Reinhard and Ben Yahia, Hamdi and Ritter, Clemens and Gaudin, Etienne and Isnard, Olivier and Whangbo, Myung-Hwan}, year={2013}, month={Aug}, pages={9627–9635} } @article{ma_liu_collins_wang_bao_xu_enriquez_chen_lin_whangbo_2013, title={Magnetic and Electrical Transport Properties of LaBaCo2O5.5+delta Thin Films on Vicinal (001) SrTiO3 Surfaces}, volume={5}, ISSN={["1944-8252"]}, DOI={10.1021/am302553y}, abstractNote={Highly epitaxial LaBaCo(2)O(5.5+δ) thin films were grown on the vicinal (001) SrTiO(3) substrates with miscut angles of 0.5°, 3.0°, and 5.0° to systemically study strain effect on its physical properties. The electronic transport properties and magnetic behaviors of these films are strongly dependent on the miscut angles. With increasing the miscut angle, the transport property of the film changes from semiconducting to semimetallic, which results most probably from the locally strained domains induced by the surface step terraces. In addition, a very large magnetoresistance (34% at 60 K) was achieved for the 0.5°-miscut film, which is ~30% larger than that for the film grown on the regular (001) SrTiO(3) substrates.}, number={2}, journal={ACS APPLIED MATERIALS & INTERFACES}, author={Ma, Chunrui and Liu, Ming and Collins, Gregory and Wang, Haibin and Bao, Shanyong and Xu, Xing and Enriquez, Erik and Chen, Chonglin and Lin, Yuan and Whangbo, Myung-Hwan}, year={2013}, month={Jan}, pages={451–455} } @article{xiang_lee_koo_gong_whangbo_2013, title={Magnetic properties and energy-mapping analysis}, volume={42}, ISSN={["1477-9234"]}, DOI={10.1039/c2dt31662e}, abstractNote={The magnetic energy levels of a given magnetic solid are closely packed in energy because the interactions between magnetic ions are weak. Thus, in describing its magnetic properties, one needs to generate its magnetic energy spectrum by employing an appropriate spin Hamiltonian. In this review article we discuss how to determine and specify a necessary spin Hamiltonian in terms of first principles electronic structure calculations on the basis of energy-mapping analysis and briefly survey important concepts and phenomena that one encounters in reading the current literature on magnetic solids. Our discussion is given on a qualitative level from the perspective of magnetic energy levels and electronic structures. The spin Hamiltonian appropriate for a magnetic system should be based on its spin lattice, i.e., the repeat pattern of its strong magnetic bonds (strong spin exchange paths), which requires one to evaluate its Heisenberg spin exchanges on the basis of energy-mapping analysis. Other weaker energy terms such as Dzyaloshinskii-Moriya (DM) spin exchange and magnetocrystalline anisotropy energies, which a spin Hamiltonian must include in certain cases, can also be evaluated by performing energy-mapping analysis. We show that the spin orientation of a transition-metal magnetic ion can be easily explained by considering its split d-block levels as unperturbed states with the spin-orbit coupling (SOC) as perturbation, that the DM exchange between adjacent spin sites can become comparable in strength to the Heisenberg spin exchange when the two spin sites are not chemically equivalent, and that the DM interaction between rare-earth and transition-metal cations is governed largely by the magnetic orbitals of the rare-earth cation.}, number={4}, journal={DALTON TRANSACTIONS}, author={Xiang, Hongjun and Lee, Changhoon and Koo, Hyun-Joo and Gong, Xingao and Whangbo, Myung-Hwan}, year={2013}, pages={823–853} } @article{guguchia_caslin_kremer_keller_shengelaya_maisuradze_bettis_kohler_bussmann-holder_whangbo_2013, title={Nonlinear pressure dependence of T-N in almost multiferroic EuTiO3}, volume={25}, number={37}, journal={Journal of Physics. Condensed Matter}, author={Guguchia, Z. and Caslin, K. and Kremer, R. K. and Keller, H. and Shengelaya, A. and Maisuradze, A. and Bettis, J. L. and Kohler, J. and Bussmann-Holder, A. and Whangbo, M. H.}, year={2013} } @article{hakouk_deniard_lajaunie_guillot-deudon_harel_wang_huang_koo_whangbo_jobic_et al._2013, title={Novel Soft-Chemistry Route of Ag2Mo3O10 center dot 2H(2)O Nanowires and in Situ Photogeneration of a Ag@Ag2Mo3O10 center dot 2H(2)O Plasmonic Heterostructure}, volume={52}, ISSN={["1520-510X"]}, DOI={10.1021/ic400343v}, abstractNote={Ultrathin Ag2Mo3O10·2H2O nanowires (NWs) were synthesized by soft chemistry under atmospheric pressure from a hybrid organic–inorganic polyoxometalate (CH3NH3)2[Mo7O22] and characterized by powder X-ray diffraction, DSC/TGA analyses, FT-IR and FT-Raman spectroscopies, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Their diameters are a few tens of nanometers and hence much thinner than that found for silver molybdates commonly obtained under hydrothermal conditions. The optical properties of Ag2Mo3O10·2H2O NWs before and after UV irradiation were investigated by UV–vis–NIR diffuse reflectance spectroscopy revealing, in addition to photoreduction of Mo6+ to Mo5+ cations, in situ photogeneration of well-dispersed silver Ag0 nanoparticles on the surface of the NWs. The resulting Ag@Ag2Mo3O10·2H2O heterostructure was confirmed by electron energy-loss spectroscopy (EELS), X-ray photoelectron spectroscopy (XPS), and Auger spectroscopy. Concomitant reduction of Mo6+ and Ag+ cations under UV excitation was discussed on the basis of electronic band structure calculations. The Ag@Ag2Mo3O10·2H2O nanocomposite is an efficient visible-light-driven plasmonic photocatalyst for degradation of Rhodamine B dye in aqueous solution.}, number={11}, journal={INORGANIC CHEMISTRY}, author={Hakouk, Khadija and Deniard, Philippe and Lajaunie, Luc and Guillot-Deudon, Catherine and Harel, Sylvie and Wang, Zeyan and Huang, Baibiao and Koo, Hyun-Joo and Whangbo, Myung-Hwan and Jobic, Stephane and et al.}, year={2013}, month={Jun}, pages={6440–6449} } @article{kasapbasi_whangbo_2013, title={On the nature of the photochemical reaction of polypyridyl Ru(II) complexes leading to sunlight-to-chemical energy conversion: density functional analysis}, volume={3}, number={24}, journal={RSC Advances}, author={Kasapbasi, E. E. and Whangbo, M. H.}, year={2013}, pages={9414–9418} } @article{brinzari_chen_sun_liu_tung_wang_schlueter_singleton_manson_whangbo_et al._2013, title={Quantum Critical Transition Amplifies Magnetoelastic Coupling in Mn[N(CN)(2)](2)}, volume={110}, ISSN={["1079-7114"]}, DOI={10.1103/physrevlett.110.237202}, abstractNote={We report the discovery of a magnetic quantum critical transition in Mn[N(CN)(2)](2) that drives the system from a canted antiferromagnetic state to the fully polarized state with amplified magnetoelastic coupling as an intrinsic part of the process. The local lattice distortions, revealed through systematic phonon frequency shifts, suggest a combined MnN(6) octahedra distortion+counterrotation mechanism that reduces antiferromagnetic interactions and acts to accommodate the field-induced state. These findings deepen our understanding of magnetoelastic coupling near a magnetic quantum critical point and away from the static limit.}, number={23}, journal={PHYSICAL REVIEW LETTERS}, author={Brinzari, T. V. and Chen, P. and Sun, Q. -C. and Liu, J. and Tung, L. -C. and Wang, Y. and Schlueter, J. A. and Singleton, J. and Manson, J. L. and Whangbo, M. -H. and et al.}, year={2013}, month={Jun} } @article{bykov_zhang_schoenleber_woelfel_ali_smaalen_glaum_koo_whangbo_reuvekamp_et al._2013, title={Spin-Peierls distortions in TiPO4}, volume={88}, ISSN={["2469-9969"]}, DOI={10.1103/physrevb.88.184420}, abstractNote={On the basis of single-crystal x-ray diffraction we show that TiPO${}_{4}$ undergoes a spin-Peierls distortion below 74.5(5) K, with a dimerization of the Ti chains along the $\mathbf{c}$ axis. Between 74.5(5) and 111.6(3) K, TiPO${}_{4}$ develops an incommensurate (IC) phase with temperature-dependent $\mathbf{q}$ vector (${\ensuremath{\sigma}}_{1}$,0,0). Density functional calculations strongly suggest that the IC phase results from a frustration of the lock-in spin-Peierls transition due to the competition of three energetically almost degenerate crystal structures and elastic coupling of the Ti chains via the bridging PO${}_{4}$ units. The phase transition into the IC phase is of second order, but the lock-in transition into the spin-Peierls distortion below 74.5 K is of weak first order in nature.}, number={18}, journal={PHYSICAL REVIEW B}, author={Bykov, Maxim and Zhang, Jian and Schoenleber, Andreas and Woelfel, Alexander and Ali, Sk Imran and Smaalen, Sander and Glaum, R. and Koo, H. -J. and Whangbo, M. -H. and Reuvekamp, P. G. and et al.}, year={2013}, month={Nov} } @article{nalbandyan_zvereva_yalovega_shukaev_ryzhakova_guda_stroppa_picozzi_vasiliev_whangbo_2013, title={Synthesis and Characterization of MnCrO4, a New Mixed-Valence Antiferromagnet}, volume={52}, ISSN={["1520-510X"]}, DOI={10.1021/ic401391b}, abstractNote={A new orthorhombic phase, MnCrO4, isostructural with MCrO4 (M = Mg, Co, Ni, Cu, Cd) was prepared by evaporation of an aqueous solution, (NH4)2Cr2O7 + 2 Mn(NO3)2, followed by calcination at 400 °C. It is characterized by redox titration, Rietveld analysis of the X-ray diffraction pattern, Cr K edge and Mn K edge XANES, ESR, magnetic susceptibility, specific heat and resistivity measurements. In contrast to the high-pressure MnCrO4 phase where both cations are octahedral, the new phase contains Cr in a tetrahedral environment suggesting the charge balance Mn(2+)Cr(6+)O4. However, the positions of both X-ray absorption K edges, the bond lengths and the ESR data suggest the occurrence of some mixed-valence character in which the mean oxidation state of Mn is higher than 2 and that of Cr is lower than 6. Both the magnetic susceptibility and the specific heat data indicate an onset of a three-dimensional antiferromagnetic order at TN ≈ 42 K, which was confirmed also by calculating the spin exchange interactions on the basis of first principles density functional calculations. Dynamic magnetic studies (ESR) corroborate this scenario and indicate appreciable short-range correlations at temperatures far above TN. MnCrO4 is a semiconductor with activation energy of 0.27 eV; it loses oxygen on heating above 400 °C to form first Cr2O3 plus Mn3O4 and then Mn1.5Cr1.5O4 spinel.}, number={20}, journal={INORGANIC CHEMISTRY}, author={Nalbandyan, Vladimir B. and Zvereva, Elena A. and Yalovega, Galina E. and Shukaev, Igor L. and Ryzhakova, Anastasiya P. and Guda, Alexander A. and Stroppa, Alessandro and Picozzi, Silvia and Vasiliev, Alexander N. and Whangbo, Myung-Hwan}, year={2013}, month={Oct}, pages={11850–11858} } @article{niu_dai_guo_ma_huang_whangbo_2013, title={Tunable topological surface and realization of insulating massive Dirac fermion state in Bi2Te2Se with co-substitution}, volume={1}, ISSN={["2050-7534"]}, DOI={10.1039/c2tc00017b}, abstractNote={The ternary topological insulator Bi2Te2Se is exceptional as it has a larger bulk resistivity than previously studied topological insulators. Here we explored the possibility of modifying the topological surface states and achieving the insulating massive Dirac fermion state in Bi2Te2Se on the basis of density functional calculations. Substitution of O for the outmost-layer Te leads to tunable surface states with an ideal Dirac cone. The co-substitution of Cr and O, as well as that of Mn and F, for the surface Bi and Te places the Dirac point inside the bulk band gap and opens a band gap at the Dirac point, hence creating the insulating massive Dirac fermion state. The co-substitution of magnetic and non-magnetic elements is a promising way of tuning the properties of topological insulators.}, number={1}, journal={JOURNAL OF MATERIALS CHEMISTRY C}, author={Niu, Chengwang and Dai, Ying and Guo, Meng and Ma, Yandong and Huang, Baibiao and Whangbo, Myung-Hwan}, year={2013}, pages={114–120} } @article{xiang_wang_whangbo_gong_2013, title={Unified model of ferroelectricity induced by spin order}, volume={88}, ISSN={["2469-9969"]}, DOI={10.1103/physrevb.88.054404}, abstractNote={For spin-order-driven ferroelectricity, a general theory that includes both purely electronic and ion-displacement contributions simultaneously is lacking. Here we present a realistic method for describing the ion-displacement part of the ferroelectricity and combine it with the pure electronic description proposed earlier to formulate a unified model that can describe any spin order including an incommensurate one. This unified model reproduces first-principles results known for representative multiferroics and provides insight into the origin of ferroelectricity and magnetoelectric coupling. We find that multiferroicity in spiral magnets LiCuVO${}_{4}$ and TbMnO${}_{3}$ can be explained by our unified model, but not by previous spin current models. The magnetoelectric effect observed for BiFeO${}_{3}$ in the cycloidal spiral state is found to originate from the exchange striction.}, number={5}, journal={PHYSICAL REVIEW B}, author={Xiang, H. J. and Wang, P. S. and Whangbo, M. -H. and Gong, X. G.}, year={2013}, month={Aug} } @article{koo_whangbo_2012, title={Analysis of the magnetic structure of the manganese oxychalcogenides R2Mn2Se2O (R=LaO, BaF) by density functional calculations}, volume={324}, ISSN={["1873-4766"]}, DOI={10.1016/j.jmmm.2012.06.035}, abstractNote={We examined the magnetic structures of R2Mn2Se2O (R=LaO, BaF) by evaluating the spin exchange interactions on the basis of density functional theory (DFT) calculations, and compared how they differ from that of the Fe analog (BaF)2Fe2Se2O. In R2Mn2Se2O (R=LaO, BaF), the two-dimensional antiferromagnetic square lattice defined by J1 is spin-frustrated, and the exchange J1 is stronger for (LaO)2Mn2Se2O than for (BaF)2Mn2Se2O by a factor of 1.5 explaining why the magnetic susceptibility maximum occurs at a higher temperature for (LaO)2Mn2Se2O than for (BaF)2Mn2Se2O (360 vs. 210 K). We identified two probable reasons why the specific heat anomaly at the long-range antiferromagnetic ordering temperature TN is significantly weaker for R2Mn2Se2O than for (BaF)2Fe2Se2O.}, number={22}, journal={JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS}, author={Koo, Hyun-Joo and Whangbo, Myung-Hwan}, year={2012}, month={Nov}, pages={3859–3862} } @article{zhao_hung_li_chen_wu_kremer_banks_simon_whangbo_lee_et al._2012, title={CuBr2-A New Multiferroic Material with High Critical Temperature}, volume={24}, ISSN={["0935-9648"]}, DOI={10.1002/adma.201200734}, abstractNote={A new multiferroic material, CuBr2, is reported for the first time. CuBr2 has not only a high transition temperature (close to liquid nitrogen temperature) but also low dielectric loss and strong magnetoelectric coupling. These findings reveal the importance of anion effects, in the search for the high temperature multiferroics materials among these low-dimensional spin systems.}, number={18}, journal={ADVANCED MATERIALS}, author={Zhao, Li. and Hung, Tsu-Lien and Li, Ching-Chien and Chen, Yang-Yuan and Wu, Maw-Kuen and Kremer, Reinhard K. and Banks, Michael G. and Simon, Arndt and Whangbo, Myung-Hwan and Lee, Changhoon and et al.}, year={2012}, month={May}, pages={2469–2473} } @article{kasapbasi_whangbo_2012, title={Density Functional Investigation of the Water Oxidation by Iron Complexes Based on Tetradentate Nitrogen Ligands}, volume={51}, ISSN={["1520-510X"]}, DOI={10.1021/ic3013359}, abstractNote={Recently it was discovered that the iron coordination complex LN4Fe(II)(OTf)2 (1) (LN4 = neutral tetraazadendate ligand and OTf = OSO2CF3) and its analogues are efficient water oxidizing catalysts (WOCs) in aqueous acidic solution with excess amount of ceric(IV) ammonium nitrate (CAN), [Ce(IV)(NO3)6](NH4)2, as sacrificial oxidants. The probable mechanism of water oxidation by these catalysts was explored on the basis of density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations for 1 as a representative WOC. We examined the conversion of 1 to the resting intermediate [LN4Fe(IV)(O)(OH2)]2+ [2(IV)] as well as two catalytic cycles involving 2(IV): one proposed by Fillol et al. [Nat. Chem. 2011, 3, 1] in which the Fe oxidation states of the intermediate species vary from +2 to +5, and the alternative cycle in which they remain constant at +4. In addition, we investigated the role of the sacrificial oxidant CAN in driving the catalytic cycle. Our DFT and TD-DFT calculations confirm the experimental observation that 2(IV) is the resting species, and indicate that the catalytic cycle in which the Fe oxidation states of the intermediate species remain at +4 is energetically more favorable.}, number={20}, journal={INORGANIC CHEMISTRY}, author={Kasapbasi, Esra E. and Whangbo, Myung-Hwan}, year={2012}, month={Oct}, pages={10850–10855} } @article{koo_lee_whangbo_2012, title={Density functional analysis of the magnetic structures of Sr2MGe2O7 (M = Mn, Co)}, volume={324}, ISSN={["1873-4766"]}, DOI={10.1016/j.jmmm.2012.06.001}, abstractNote={Abstract To examine the difference between the magnetic structures of Sr2MGe2O7 (M=Mn, Co), we evaluated their spin exchange interactions by performing energy-mapping analysis based on density functional theory calculations. The calculated intra- and inter-layer spin exchanges correctly predict the G-type and C-type antiferromagnetic structures of Sr2MnGe2O7 and Sr2CoGe2O7, respectively, and the Curie–Weiss temperatures estimated from these spin exchanges are also in good agreement with the experiment. The ∥c and ⊥c orientations of the spins in the ordered magnetic structures of Sr2MnGe2O7 and Sr2CoGe2O7, respectively, were also examined by considering spin–orbit coupling.}, number={22}, journal={JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS}, author={Koo, Hyun-Joo and Lee, Changhoon and Whangbo, Myung-Hwan}, year={2012}, month={Nov}, pages={3716–3718} } @article{lu_whangbo_dong_gong_xiang_2012, title={Giant Ferroelectric Polarization of CaMn7O12 Induced by a Combined Effect of Dzyaloshinskii-Moriya Interaction and Exchange Striction}, volume={108}, ISSN={["0031-9007"]}, DOI={10.1103/physrevlett.108.187204}, abstractNote={By extending our general spin-current model to non-centrosymmetric spin dimers and performing density functional calculations, we investigate the causes for the helical magnetic order and the origin of the giant ferroelectric polarization of CaMn7O12. The giant ferroelectric polarization is proposed to be caused by the symmetric exchange striction due to the canting of the Mn4+ spin arising from its strong Dzyaloshinskii-Moriya (DM) interaction. Our study suggests that CaMn7O12 may exhibit a novel magnetoelectric coupling mechanism in which the magnitude of the polarization is governed by the exchange striction, but the direction of the polarization by the chirality of the helical magnetic order.}, number={18}, journal={PHYSICAL REVIEW LETTERS}, author={Lu, X. Z. and Whangbo, M. -H. and Dong, Shuai and Gong, X. G. and Xiang, H. J.}, year={2012}, month={May} } @article{liu_ma_liu_collins_chen_he_jiang_meletis_sun_jacobson_et al._2012, title={Giant Magnetoresistance and Anomalous Magnetic Properties of Highly Epitaxial Ferromagnetic LaBaCo2O5.5+delta Thin Films on (001) MgO}, volume={4}, ISSN={["1944-8244"]}, DOI={10.1021/am301427c}, abstractNote={Ferromagnetic thin films of the A-site nano-ordered double perovskite LaBaCo(2)O(5.5+δ) (LBCO) were grown on (001) MgO, and their structural and magnetic properties were characterized. The as-grown films have an excellent epitaxial behavior with atomically sharp interfaces, with the c-axis of the LBCO structure lying in the film plane and the interface relationship given by (100)(LBCO)//(001)(MgO) and [001](LBCO)//[100](MgO) or [010](MgO). The as-grown LBCO films exhibit a giant magnetoresistance (54% at 40 K under 7 T) and an anomalous magnetic hysteresis, depending strongly on the temperature and the applied magnetic field scan width.}, number={10}, journal={ACS APPLIED MATERIALS & INTERFACES}, author={Liu, Ming and Ma, Chunrui and Liu, Jian and Collins, Gregory and Chen, Chonglin and He, Jie and Jiang, Jiechao and Meletis, Efstathios I. and Sun, Li and Jacobson, Allan J. and et al.}, year={2012}, month={Oct}, pages={5524–5528} } @article{li_whangbo_gong_xiang_2012, title={Helicoidal magnetic structure and ferroelectric polarization in Cu3Nb2O8}, volume={86}, ISSN={["1098-0121"]}, DOI={10.1103/physrevb.86.174401}, abstractNote={We investigate the origin of the coplanar helicoidal magnetic structure and the ferroelectric polarization in Cu${}_{3}$Nb${}_{2}$O${}_{8}$ by combining first-principles calculations and our spin-induced ferroelectric polarization model. The coplanar helicoidal spin state comes from the competition between the isotropic exchange interactions and the ferroelectric polarization from the symmetric exchange striction with slight spin canting. However, the direction of the polarization is not determined by the orientation of the spin rotation plane.}, number={17}, journal={PHYSICAL REVIEW B}, author={Li, Zheng-Lu and Whangbo, M. -H. and Gong, X. G. and Xiang, H. J.}, year={2012}, month={Nov} } @article{zheng_huang_lu_wang_qin_zhang_dai_whangbo_2012, title={Hydrogenated titania: synergy of surface modification and morphology improvement for enhanced photocatalytic activity}, volume={48}, number={46}, journal={Chemical Communications}, author={Zheng, Z. K. and Huang, B. B. and Lu, J. B. and Wang, Z. Y. and Qin, X. Y. and Zhang, X. Y. and Dai, Y. and Whangbo, M. H.}, year={2012}, pages={5733–5735} } @article{schlueter_park_halder_armand_dunmars_chapman_manson_singleton_mcdonald_plonczak_et al._2012, title={Importance of Halogen center dot center dot center dot Halogen Contacts for the Structural and Magnetic Properties of CuX2(pyrazine-N,N '-dioxide)(H2O)(2) (X = Cl and Br)}, volume={51}, number={4}, journal={Inorganic Chemistry}, author={Schlueter, J. A. and Park, H. and Halder, G. J. and Armand, W. R. and Dunmars, C. and Chapman, K. W. and Manson, J. L. and Singleton, J. and McDonald, R. and Plonczak, A. and et al.}, year={2012}, pages={2121–2129} } @article{meddar_josse_maglione_guiet_la_deniard_decourt_lee_tian_jobic_et al._2012, title={Increasing the Phase-Transition Temperatures in Spin-Frustrated Multiferroic MnWO4 by Mo Doping}, volume={24}, ISSN={["1520-5002"]}, DOI={10.1021/cm2031653}, abstractNote={Ceramic samples of MnW1–xMoxO4 (x ≤ 0.3) solid solution were prepared by a solid-state route with the goal of increasing the magnitude of the spin-exchange couplings among the Mn2+ ions in the spin spiral multiferroic MnWO4. Samples were characterized by X-ray diffraction, optical spectroscopy, magnetization, and dielectric permittivity measurements. It was observed that the Néel temperature TN, the spin spiral ordering temperature TM2, and the ferroelectric phase-transition temperature TFE2 of MnWO4 increased upon the nonmagnetic substitution of Mo6+ for W6+. Like pure MnWO4, the ferroelectric critical temperature TFE2(x) coincides with the magnetic ordering temperature TM2(x). A density functional analysis of the spin-exchange interactions for a hypothetical MnMoO4 that is isostructural with MnWO4 suggests that Mo substitution increases the strength of the spin-exchange couplings among Mn2+ in the vicinity of a Mo6+ ion. Our study shows that the Mo-doped MnW1–xMoxO4 (x ≤ 0.3) compounds are spin-frustrated materials that have higher magnetic and ferroelectric phase-transition temperatures than does pure MnWO4.}, number={2}, journal={CHEMISTRY OF MATERIALS}, author={Meddar, Lynda and Josse, Michael and Maglione, Mario and Guiet, Amandine and La, Carole and Deniard, Philippe and Decourt, Rodolphe and Lee, Changhoon and Tian, Chuan and Jobic, Stephane and et al.}, year={2012}, month={Jan}, pages={353–360} } @article{manson_carreiro_lapidus_stephens_goddard_del sesto_bendix_ghannadzadeh_franke_singleton_et al._2012, title={Influence of HF2- geometry on magnetic interactions elucidated from polymorphs of the metal-organic framework [Ni(HF2)(pyz)(2)]PF6 (pyz = pyrazine)}, volume={41}, number={24}, journal={Dalton Transactions (Cambridge, England : 2003)}, author={Manson, J. L. and Carreiro, K. E. and Lapidus, S. H. and Stephens, P. W. and Goddard, P. A. and Del Sesto, R. E. and Bendix, J. and Ghannadzadeh, S. and Franke, I. and Singleton, J. and et al.}, year={2012}, pages={7235–7243} } @article{lee_liu_whangbo_koo_kremer_simon_2012, title={Investigation of the spin exchange interactions and the magnetic structure of the high-temperature multiferroic CuBr2}, volume={86}, ISSN={["2469-9969"]}, DOI={10.1103/physrevb.86.060407}, abstractNote={We report a detailed density functional analysis of the spin exchange interactions and the magnetic structure of the high-temperature multiferroic CuBr${}_{2}$ and compare the results with magnetic susceptibility measurements. CuBr${}_{2}$ shows one-dimensional antiferromagnetism and undergoes long-range antiferromagnetic ordering at $\ensuremath{\sim}$74 K. Due to the competition between the nearest- and next-nearest-neighbor spin exchanges, each Cu${}^{2+}$ chain has a cycloidal spin-spiral structure, which is described approximately by a quadrupling of the nuclear cell with spin moment rotation of $\ensuremath{\sim}$${85}^{\ensuremath{\circ}}$ in the plane of the CuBr${}_{2}$ ribbon plane.}, number={6}, journal={PHYSICAL REVIEW B}, author={Lee, C. and Liu, Jia and Whangbo, M. -H. and Koo, H. -J. and Kremer, R. K. and Simon, A.}, year={2012}, month={Aug} } @article{koo_kremer_whangbo_2012, title={Non-idle-spin behavior and field-induced magnetic transitions of the triple chain magnet Cu-3(OH)(4)SO4}, volume={81}, number={6}, journal={Journal of the Physical Society of Japan}, author={Koo, H. J. and Kremer, R. K. and Whangbo, M. H.}, year={2012} } @article{tong_koehler_simon_lee_whangbo_2012, title={Optical Properties of the Orchid Colored Silver(II) Fluoride Cs2AgF4}, volume={638}, ISSN={["0044-2313"]}, DOI={10.1002/zaac.201200315}, abstractNote={Abstract Orchid colored powder samples of Cs 2 AgF 4 were prepared by a solid state reaction from CsF and AgF 2 . The diffuse reflectance spectrum of a powder sample of Cs 2 AgF 4 was measured in the UV/Vis region. It shows three broad bands, two in the visible‐light region at 650 nm, 500 nm and one in the UV region at 259 nm. The bands are assigned to F 2p → Ag 4d and Ag 4d → Ag 4d transitions. The optical band gap for Cs 2 AgF 4 determined from the UV/Vis diffuse reflectance spectrum is approx. 2.17 eV. In order to interpret the observed absorptions, the theoretical absorption spectrum of Cs 2 AgF 4 was obtained from density functional calculations.}, number={11}, journal={ZEITSCHRIFT FUR ANORGANISCHE UND ALLGEMEINE CHEMIE}, author={Tong, Jianwei and Koehler, Juergen and Simon, Arndt and Lee, Changhoon and Whangbo, Myung-Hwan}, year={2012}, month={Sep}, pages={1792–1795} } @article{wang_huang_dai_whangbo_2012, title={Plasmonic photocatalysts: Harvesting visible light with noble metal nanoparticles}, volume={14}, number={28}, journal={Physical Chemistry Chemical Physics}, author={Wang, P. and Huang, B. B. and Dai, Y. and Whangbo, M. H.}, year={2012}, pages={9813–9825} } @article{lee_kan_xiang_kremer_lee_hiroi_whangbo_2012, title={Spin Reorientation in the Square-Lattice Antiferromagnets RMnAsO (R = Ce, Nd): Density Functional Analysis of the Spin-Exchange Interactions between the Rare-Earth and Transition-Metal Ions}, volume={51}, ISSN={["1520-510X"]}, DOI={10.1021/ic300685d}, abstractNote={The spin reorientation (SR) phenomenon of the square-lattice antiferromagnets RMnAsO (R = Ce, Nd) was investigated by analyzing the spin-exchange interactions between the rare-earth and the transition-metal ions (R3+ and Mn2+, respectively) on the basis of density functional calculations. It is found that the symmetry and strength of the Dzyaloshinskii–Moriya (DM) interaction are determined primarily by the partially filled 4f states of the R3+ ions and that the DM and biquadratic (BQ) exchanges between the R3+ and the Mn2+ ions are unusually strong and control the observed spin reorientation phenomenon. Below their SR temperature, the Mn2+ and Ce3+ moments are orthogonal in CeMnAsO but are collinear in NdMnAsO, because the DM interaction dominates over the BQ interaction for CeMnAsO, while the opposite is the case for NdMnAsO. Experiments designed to test the implications of our findings are proposed.}, number={12}, journal={INORGANIC CHEMISTRY}, author={Lee, Changhoon and Kan, Erjun and Xiang, Hongjun and Kremer, Reinhard K. and Lee, Seung-Hun and Hiroi, Zenji and Whangbo, Myung-Hwan}, year={2012}, month={Jun}, pages={6890–6897} } @article{lee_kan_whangbo_bussmann-holder_simon_2012, title={Spin/Charge Redistributions and Oxygen Atom Displacements Induced by Spin Flip and Hole Doping in the CuO2 Layer of High-Temperature Superconductors}, volume={25}, ISSN={["1557-1939"]}, DOI={10.1007/s10948-011-1208-3}, number={1}, journal={JOURNAL OF SUPERCONDUCTIVITY AND NOVEL MAGNETISM}, author={Lee, C. and Kan, E. J. and Whangbo, M. -H. and Bussmann-Holder, A. and Simon, A.}, year={2012}, month={Jan}, pages={55–59} } @article{yang_li_lu_whangbo_wei_gong_xiang_2012, title={Strong Dzyaloshinskii-Moriya Interaction and Origin of Ferroelectricity in Cu2OSeO3}, volume={109}, ISSN={["1079-7114"]}, DOI={10.1103/physrevlett.109.107203}, abstractNote={By performing density functional calculations, we investigate the origin of the skyrmion state and ferroelectricity in Cu2OSeO3. We find that the Dzyaloshinskii-Moriya interactions between the two different kinds of Cu ions are extremely strong and induce the helical ground state and the skyrmion state in the absence and presence of magnetic field, respectively. On the basis of the general model for the spin-order induced polarization, we propose that the ferroelectric polarization of Cu2OSeO3 in the collinear ferrimagnetic state arises from an unusual mechanism, i.e., the single-spin-site contribution due to the spin-orbit coupling.}, number={10}, journal={PHYSICAL REVIEW LETTERS}, author={Yang, J. H. and Li, Z. L. and Lu, X. Z. and Whangbo, M. -H. and Wei, Su-Huai and Gong, X. G. and Xiang, H. J.}, year={2012}, month={Sep} } @article{ben yahia_shikano_koike_tatsumi_kobayashi_kawaji_avdeev_miiller_ling_liu_et al._2012, title={Synthesis and characterization of the crystal structure and magnetic properties of the new fluorophosphate LiNaCo[PO4]F}, volume={51}, DOI={10.1021/ic300374w}, abstractNote={The new compound LiNaCo[PO(4)]F was synthesized by a solid state reaction route, and its crystal structure was determined by single-crystal X-ray diffraction measurements. The magnetic properties of LiNaCo[PO(4)]F were characterized by magnetic susceptibility, specific heat, and neutron powder diffraction measurements and also by density functional calculations. LiNaCo[PO(4)]F crystallizes with orthorhombic symmetry, space group Pnma, with a = 10.9334(6), b = 6.2934(11), c = 11.3556(10) Å, and Z = 8. The structure consists of edge-sharing CoO(4)F(2) octahedra forming CoFO(3) chains running along the b axis. These chains are interlinked by PO(4) tetrahedra forming a three-dimensional framework with the tunnels and the cavities filled by the well-ordered sodium and lithium atoms, respectively. The magnetic susceptibility follows the Curie-Weiss behavior above 60 K with θ = -21 K. The specific heat and magnetization measurements show that LiNaCo[PO(4)]F undergoes a three-dimensional magnetic ordering at T(mag) = 10.2(5) K. The neutron powder diffraction measurements at 3 K show that the spins in each CoFO(3) chain along the b-direction are ferromagnetically coupled, while these FM chains are antiferromagnetically coupled along the a-direction but have a noncollinear arrangement along the c-direction. The noncollinear spin arrangement implies the presence of spin conflict along the c-direction. The observed magnetic structures are well explained by the spin exchange constants determined from density functional calculations.}, number={16}, journal={Inorganic Chemistry}, author={Ben Yahia, H. and Shikano, M. and Koike, S. and Tatsumi, K. and Kobayashi, H. and Kawaji, H. and Avdeev, M. and Miiller, W. and Ling, C. D. and Liu, J. and et al.}, year={2012}, pages={8729–8738} } @article{zhang_dai_yu_guo_huang_whangbo_2012, title={The surface termination effect on the quantum confinement and electron affinities of 3C-SiC quantum dots: a first-principles study}, volume={4}, number={5}, journal={Nanoscale}, author={Zhang, Z. K. and Dai, Y. and Yu, L. and Guo, M. and Huang, B. B. and Whangbo, M. H.}, year={2012}, pages={1592–1597} } @article{kim_kim_rhee_kim_whangbo_2012, title={Tip-Induced Modification of Polyoxometalate-Dodecane Thiol Self-Assembled Monolayers on Au(111) during Scanning Tunneling Microscopy Imaging}, volume={33}, ISSN={["0253-2964"]}, DOI={10.5012/bkcs.2012.33.9.3139}, abstractNote={Department of Chemistry, North Carolina State University, Raleigh, NC 27695, USAReceived June 14, 2012, Accepted June 26, 2012Key Words : Au(111), Polyoxometalate, Self-assembled monolayer, Dodecanethiol, Scanning tunneling mi-croscopySelf-assembled monolayers (SAMs) of thiolates on Ausurfaces have been extensively investigated for the last fewdecades because such systems offer useful applications inthe field of nanoscience and nanotechnology.}, number={9}, journal={BULLETIN OF THE KOREAN CHEMICAL SOCIETY}, author={Kim, Jandee and Kim, Hyeran and Rhee, Choong Kyun and Kim, Jongwon and Whangbo, Myung Hwan}, year={2012}, month={Sep}, pages={3139–3141} } @article{manson_baldwin_scott_bendix_del sesto_goddard_kohama_tran_ghannadzadeh_singleton_et al._2012, title={[Ni(HF2)(3-Clpy)(4)]BF4 (py = pyridine): Evidence for spin exchange along strongly distorted F center dot center dot center dot H center dot center dot center dot F- bridges in a one-dimensional polymeric chain}, volume={51}, number={14}, journal={Inorganic Chemistry}, author={Manson, J. L. and Baldwin, A. G. and Scott, B. L. and Bendix, J. and Del Sesto, R. E. and Goddard, P. A. and Kohama, Y. and Tran, H. E. and Ghannadzadeh, S. and Singleton, J. and et al.}, year={2012}, pages={7520–7528} } @article{tsukamoto_okamoto_matsuhira_whangbo_hiroi_2011, title={A magnetic transition probed by the Ce ion in square-lattice antiferromagnet CeMnAsO}, volume={80}, number={9}, journal={Journal of the Physical Society of Japan}, author={Tsukamoto, Y. and Okamoto, Y. and Matsuhira, K. and Whangbo, M. H. and Hiroi, Z.}, year={2011} } @article{zhao_nellutla_son_vaughn_ye_smith_caignaert_lufaso_pekarek_smirnov_et al._2011, title={Ba4KFe3O9: A Novel Ferrite Containing Discrete 6-Membered Rings of Corner-Sharing FeO4 Tetrahedra}, volume={50}, ISSN={["1520-510X"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-80053934262&partnerID=MN8TOARS}, DOI={10.1021/ic201374g}, abstractNote={Single crystals of a new iron-containing oxide, Ba4KFe3O9, were grown from a hydroxide melt, and the crystal structure was determined by single-crystal X-ray diffraction. This ferrite represents the first complex oxide containing isolated 6-membered rings of corner-sharing FeO4 tetrahedra. Mössbauer measurements are indicative of two tetrahedral high-spin Fe3+ coordination environments. The observed magnetic moment (∼3.9 μB) at 400 K is significantly lower than the calculated spin-only (∼5.2 μB) value, indicating the presence of strong antiferromagnetic interactions in the oxide. Our density functional theory calculations confirm the strong antiferromagnetic coupling between adjacent Fe3+ sites within each 6-membered ring and estimate the nearest-neighbor spin-exchange integral as ∼200 K; next-nearest-neighbor interactions are shown to be negligible. The lower than expected effective magnetic moment for Ba4KFe3O9 calculated from χT data is explained as resulting from the occupation of lower-lying magnetic states in which more spins are paired. X-band (9.5 GHz) electron paramagnetic resonance (EPR) spectra of a powder sample consist of a single line at g ∼ 2.01 that is characteristic of Fe3+ ions in a tetrahedral environment, thus confirming the Mössbauer results. Further analysis of the EPR line shape reveals the presence of two types of Fe6 magnetic species with an intensity ratio of ∼1:9. Both species have Lorentzian line shapes and indistinguishable g factors but differ in their peak-to-peak line widths (δBpp). The line-width ratio δBpp(major)/δBpp(minor) ∼ 3.6 correlates well with the ratio of the Weiss constants, θminor/θmajor ∼ 4.}, number={20}, journal={INORGANIC CHEMISTRY}, publisher={American Chemical Society (ACS)}, author={Zhao, Qingbiao and Nellutla, Saritha and Son, Won-Joon and Vaughn, Shae A. and Ye, Longfei and Smith, Mark D. and Caignaert, Vincent and Lufaso, Michael and Pekarek, Thomas M. and Smirnov, Alex I. and et al.}, year={2011}, month={Oct}, pages={10310–10318} } @article{son_manuel_adroja_whangbo_2011, title={Density Functional Analysis of the Magnetic Structure of Li3RuO4: Importance of the Ru-O center dot center dot center dot O-Ru Spin-Exchange Interactions and Substitutional Ru Defects at the Li Sites}, volume={50}, ISSN={["1520-510X"]}, DOI={10.1021/ic201023j}, abstractNote={We evaluated the spin-exchange interactions of Li3RuO4 by performing energy-mapping analysis based on density functional calculations and examined the nature of its magnetic transition at T1 = 66 K and the divergence of the field-cooled and zero-field-cooled susceptibilities below T2 = 32 K. Our study shows that T1 is associated with a three-dimensional antiferromagnetic ordering, in which the two-dimensional antiferromagnetic lattices parallel to the ab plane are antiferromagnetically coupled along the c direction. We examined how the substitutional defects, Ru atoms residing in the Li sites, affect the antiferromagnetic coupling along the c direction to explain why the expected c-axis doubling is not detected from powder neutron diffraction measurements. The susceptibility divergence below T2 is attributed to a slight spin canting out of the ab plane.}, number={19}, journal={INORGANIC CHEMISTRY}, author={Son, Won-Joon and Manuel, Pascal and Adroja, Devashibhai and Whangbo, Myung-Hwan}, year={2011}, month={Oct}, pages={9400–9405} } @article{zhang_whangbo_2011, title={Density Functional Analysis of the Spin Exchange Interactions and Charge Order Patterns in the Layered Magnetic Oxides YBaM2O5 (M = Mn, Fe, Co)}, volume={50}, ISSN={["0020-1669"]}, DOI={10.1021/ic200963g}, abstractNote={The spin and charge order phenomena of the layered magnetic oxides YBaM2O5 (M = Mn, Fe, Co) were analyzed on the basis of density functional calculations. We evaluated the spin exchange interactions of YBaM2O5 by performing energy-mapping analysis based on density functional calculations to find why they undergo a three-dimensional magnetic ordering at high temperature. We estimated the relative stabilities of the checkerboard and stripe charge order patterns of YBaM2O5 (M = Mn, Fe, Co) by optimizing their structures with density functional calculations to probe if the nature of the charge order pattern depends on whether their transition-metal ions are Jahn–Teller active.}, number={21}, journal={INORGANIC CHEMISTRY}, author={Zhang, Yuemei and Whangbo, Myung-Hwan}, year={2011}, month={Nov}, pages={10643–10647} } @article{zhang_kan_whangbo_2011, title={Density Functional Investigation of the Difference in the Magnetic Structures of the Layered Triangular Antiferromagnets CuFeO2 and AgCrO2}, volume={23}, ISSN={["1520-5002"]}, DOI={10.1021/cm2011567}, abstractNote={The layered triangular antiferromagnets CuFeO2 and AgCrO2 exhibit ferroelectric polarization when they adopt a helical spiral-spin magnetic structure. Application of magnetic field parallel to the c-axis or doping Fe sites with Al or Ga is necessary for CuFeO2 to have a helical spiral spin order. However, AgCrO2 adopts a helical spiral spin order in the absence of such extrinsic factors. A probable cause for this difference between the two systems was examined by evaluating the relative stabilities of their helical spiral and collinear spin structures on the basis of density functional calculations. In contrast to the case of AgCrO2, the collinear ↑↑↓↓ state is only slightly higher in energy than the helical spiral-spin state Qa+b in CuFeO2 so that extrinsic factors such as oxygen vacancy and applied magnetic field can influence whether CuFeO2 adopts the ↑↑↓↓ or Qa+b structure.}, number={18}, journal={CHEMISTRY OF MATERIALS}, author={Zhang, Yuemei and Kan, Erjun and Whangbo, Myung-Hwan}, year={2011}, month={Sep}, pages={4181–4185} } @article{zhang_kan_xiang_villesuzanne_whangbo_2011, title={Density Functional Theory Analysis of the Interplay between Jahn-Teller Instability, Uniaxial Magnetism, Spin Arrangement, Metal-Metal Interaction, and Spin-Orbit Coupling in Ca3CoMO6 (M = Co, Rh, Ir)}, volume={50}, ISSN={["0020-1669"]}, DOI={10.1021/ic1022278}, abstractNote={In the isostructural oxides Ca(3)CoMO(6) (M = Co, Rh, Ir), the CoMO(6) chains made up of face-sharing CoO(6) trigonal prisms and MO(6) octahedra are separated by Ca atoms. We analyzed the magnetic and electronic properties of these oxides on the basis of density functional theory calculations including on-site repulsion and spin-orbit coupling, and examined the essential one-electron pictures hidden behind results of these calculations. Our analysis reveals an intimate interplay between Jahn-Teller instability, uniaxial magnetism, spin arrangement, metal-metal interaction, and spin-orbit coupling in governing the magnetic and electronic properties of these oxides. These oxides undergo a Jahn-Teller distortion, but their distortions are weak, so that their trigonal-prism Co(n+) (n = 2, 3) ions still give rise to strong easy-axis anisotropy along the chain direction. As for the d-state split pattern of these ions, the electronic and magnetic properties of Ca(3)CoMO(6) (M = Co, Rh, Ir) are consistent with d(0) < (d(2), d(-2)) < (d(1), d(-1)) but not with (d(2), d(-2)) < d(0) < (d(1), d(-1)). The trigonal-prism Co(3+) ion in Ca(3)Co(2)O(6) has the L = 2 configuration (d(0))(1)(d(2), d(-2))(3)(d(1), d(-1))(2) because of the metal-metal interaction between adjacent Co(3+) ions in each Co(2)O(6) chain, which is mediated by their z(2) orbitals, and the spin-orbit coupling of the trigonal-prism Co(3+) ion. The spins in each CoMO(6) chain of Ca(3)CoMO(6) prefer the ferromagnetic arrangement for M = Co and Rh but the antiferromagnetic arrangement for M = Ir. The octahedral M(4+) ion of Ca(3)CoMO(6) has the (1a)(1)(1e)(4) configuration for M = Rh but the (1a)(2)(1e)(3) configuration for M = Ir, which arises from the difference in the spin-orbit coupling of the M(4+) ions and the Co···M metal-metal interactions.}, number={5}, journal={INORGANIC CHEMISTRY}, author={Zhang, Yuemei and Kan, Erjun and Xiang, Hongjun and Villesuzanne, Antoine and Whangbo, Myung-Hwan}, year={2011}, month={Mar}, pages={1758–1766} } @article{hoch_simon_lee_whangbo_koehler_2011, title={Density functional analysis of the electronic structure of Cs9InO4: Evidence for the presence of a Cs- anion}, volume={226}, ISSN={["2196-7105"]}, DOI={10.1524/zkri.2011.1371}, abstractNote={The complex oxoindate Cs9InO4, described by the electron counting (Cs+)8Cs—[(In3+)(O2–)4] + 2e−, consists of InO4 tetrahedra and Cs(Cs)16 clusters. In each Cs(Cs)16 cluster a Cs atom is located at the center of the (Cs)16 cage, and the Cs9 sublattice of Cs9InO4 is obtained from the face- and edge-sharing of the Cs(Cs)16 clusters. To examine the charge density distribution among the Cs atoms in each Cs(Cs)16 cluster, density functional calculations were carried out for Cs9InO4, and the results were analyzed. Our analysis indicates that, to a first approximation, the Cs atom located at the center of each Cs(Cs)16 is best described as Cs– anion.}, number={7}, journal={ZEITSCHRIFT FUR KRISTALLOGRAPHIE-CRYSTALLINE MATERIALS}, author={Hoch, Constantin and Simon, Arndt and Lee, Changhoon and Whangbo, Myung-Hwan and Koehler, Juergen}, year={2011}, pages={553–556} } @article{tong_kraus_koehler_simon_liu_whangbo_2011, title={Dimers of Ag2+ Ions - Synthesis and Characterization of the Quaternary Silver Fluoride Ag2ZnZr2F14 with [Ag2F7](3-) Units}, volume={637}, ISSN={["1521-3749"]}, DOI={10.1002/zaac.201100129}, abstractNote={Abstract Deep blue‐violet colored powder samples of Ag 2 ZnZr 2 F 14 were synthesized by heating Zn(NO 3 ) 2 ·4H 2 O, Ag and ZrOCl 2 ·8H 2 O at 300 °C under fluorine atmosphere. The crystal structure of Ag 2 ZnZr 2 F 14 was refined from X‐ray powder diffraction data using the Rietveld method ( C 2/ m, a = 9.0206(1) Å, b = 6.6373(1) Å, c = 9.0563(1) Å, β = 90.44(1)°, Z = 2). The structure is derived from the isotypic Ag 3 Zr 2 F 14 by replacing only one of the two crystallographically different Ag 2+ ions with Zn 2+ ions, thus leading to discrete Ag 2 F 7 dimers. These dimers are connected via nearly linear Ag–F···F–Ag bridges with short F···F distances of 2.33 Å to form two‐legged ladders. Magnetic susceptibility measurements and density functional calculations show that the two Ag 2+ ions in each Ag 2 F 7 dimer are strongly coupled antiferromagnetically.}, number={9}, journal={ZEITSCHRIFT FUR ANORGANISCHE UND ALLGEMEINE CHEMIE}, author={Tong, Jianwei and Kraus, Florian and Koehler, Juergen and Simon, Arndt and Liu, Jia and Whangbo, Myung-Hwan}, year={2011}, month={Jul}, pages={1118–1121} } @article{zheng_huang_qin_zhang_dai_whangbo_2011, title={Facile in situ synthesis of visible-light plasmonic photocatalysts M@TiO2 (M = Au, Pt, Ag) and evaluation of their photocatalytic oxidation of benzene to phenol}, volume={21}, number={25}, journal={Journal of Materials Chemistry}, author={Zheng, Z. K. and Huang, B. B. and Qin, X. Y. and Zhang, X. Y. and Dai, Y. and Whangbo, M. H.}, year={2011}, pages={9079–9087} } @article{wang_huang_wang_wang_cheng_zheng_qin_zhang_dai_whangbo_2011, title={Facile synthesis of Zn-rich (GaN)(1-x)(ZnO)(x) solid solutions using layered double hydroxides as precursors}, volume={21}, number={12}, journal={Journal of Materials Chemistry}, author={Wang, J. P. and Huang, B. B. and Wang, Z. Y. and Wang, P. and Cheng, H. F. and Zheng, Z. K. and Qin, X. Y. and Zhang, X. Y. and Dai, Y. and Whangbo, M. H.}, year={2011}, pages={4562–4567} } @article{xiang_kan_zhang_whangbo_gong_2011, title={General Theory for the Ferroelectric Polarization Induced by Spin-Spiral Order}, volume={107}, ISSN={["0031-9007"]}, DOI={10.1103/physrevlett.107.157202}, abstractNote={The ferroelectric polarization of triangular-lattice antiferromagnets induced by helical spin-spiral order is not explained by any existing model of magnetic-order-driven ferroelectricity. We resolve this problem by developing a general theory for the ferroelectric polarization induced by spin-spiral order and then by evaluating the coefficients needed to specify the general theory on the basis of density functional calculations. Our theory correctly describes the ferroelectricity of triangular-lattice antiferromagnets driven by helical spin-spiral order and incorporates known models of magnetic-order-driven ferroelectricity as special cases.}, number={15}, journal={PHYSICAL REVIEW LETTERS}, author={Xiang, H. J. and Kan, E. J. and Zhang, Y. and Whangbo, M. -H. and Gong, X. G.}, year={2011}, month={Oct} } @article{kan_wu_xiang_yang_whangbo_2011, title={Half-Metallic Dirac Point in B-Edge Hydrogenated BN Nanoribbons}, volume={115}, ISSN={["1932-7447"]}, DOI={10.1021/jp2015269}, abstractNote={The BN zigzag nanoribbons (BNZNRs) were examined by first-principles density functional calculations, including structural relaxation. The quantum confinement and edge effects of the BNZNRs produce a magnetic ground state. When the B-edge is hydrogenated, the BNZNRs possess a new state with a spin-resloved Dirac point Fermi surface, which paves a way to realizing spin-polarized massless carriers.}, number={35}, journal={JOURNAL OF PHYSICAL CHEMISTRY C}, author={Kan, Erjun and Wu, Fang and Xiang, Hongjun and Yang, Jinlong and Whangbo, Myung-Hwan}, year={2011}, month={Sep}, pages={17252–17254} } @article{zhao_darriet_whangbo_ye_stackhouse_loye_2011, title={Intriguing Interconnections Among Phase Transition, Magnetic Moment, and Valence Disproportionation in 2H-Perovskite Related Oxides}, volume={133}, ISSN={["1520-5126"]}, DOI={10.1021/ja209198b}, abstractNote={In this paper we report the crystal growth, structure determination, and magnetic properties of the 2H-perovskite related oxides, Sr(5)Co(4)O(12) and Sr(6)Co(5)O(15), as well as the charge disproportionation and associated phase transition of Sr(5)Co(4)O(12). Sr(5)Co(4)O(12) and Sr(6)Co(5)O(15) are the (m = 2, n = 3) and (m = 1, n = 1) members of the A(3m+3n)A'(n)B(3m+n)O(9m+6n) family, respectively. Sr(6)Co(5)O(15) crystallizes in the space group R32 with lattice parameters of a = 9.5020(10) Å and c = 12.379(8) Å. The structure solution shows that Sr(6)Co(5)O(15) is isostructural with Sr(6)Rh(5)O(15). Magnetic measurements do not indicate any long-range magnetic order, although the Weiss temperature of -248 K indicates the presence of dominant antiferromagnetic interactions. Sr(5)Co(4)O(12) crystallizes in the space group P-3c1 with lattice parameters of a = 9.4705(10) Å and c = 20.063(5) Å at room temperature. The single crystal structure solution revealed that the cobalt ions in the trigonal prismatic sites of Sr(5)Co(4)O(12) undergo a structural transition at ~170 K, where the cobalt atoms are in the center of the trigonal prisms below this temperature and move partially toward the faces above this temperature. This structure transition is accompanied by a change in the magnetic moment of the oxide and can be related to a valence disproportionation of the cobalt ions and a concomitant Jahn-Teller distortion. In addition, specific heat, Seebeck coefficient, electric conductivity, and magnetic measurements as well as bond valence sum calculations were carried out for Sr(5)Co(4)O(12). Sr(5)Co(4)O(12) exhibits strong magnetic anisotropy but no long-range magnetic order.}, number={51}, journal={JOURNAL OF THE AMERICAN CHEMICAL SOCIETY}, author={Zhao, Qingbiao and Darriet, Jacques and Whangbo, Myung-Hwan and Ye, Longfei and Stackhouse, Chavis and Loye, Hans-Conrad}, year={2011}, month={Dec}, pages={20981–20994} } @misc{whangbo_lee_kohler_2011, title={Metal Anions in Metal-Rich Compounds and Polar Intermetallics}, number={26}, journal={European Journal of Inorganic Chemistry}, author={Whangbo, M. H. and Lee, C. and Kohler, J.}, year={2011}, pages={3841–3847} } @article{manuel_adroja_lindgard_hillier_battle_son_whangbo_2011, title={Neutron scattering and mu SR investigations of quasi-one-dimensional magnetism in the spin=3/2 compound Li3RuO4}, volume={84}, ISSN={["2469-9969"]}, DOI={10.1103/physrevb.84.174430}, abstractNote={The $S$ = 3/2, quasi-one-dimensional (1D) zig-zag chain Heisenberg antiferromagnet Li${}_{3}$RuO${}_{4}$ has been investigated using heat capacity, inelastic neutron scattering, neutron diffraction, and \ensuremath{\mu}SR measurements on a powder sample. Our neutron diffraction and \ensuremath{\mu}SR studies confirm a long-range ordering of the magnetic moments on the Ru${}^{5+}$ cations below 40 K. The magnetic excitations were measured at various temperatures above and below the three-dimensional (3D) ordering temperature in order to understand the broad peak observed in the temperature dependence of the magnetic susceptibility. At 5 K we have observed two well-defined magnetic excitations at 5.5 meV and 8.5 meV and a weak low-energy peak near \ensuremath{\sim}2 meV. We interpret the 5.5 meV energy peak as a 1D zone-boundary mode and that at 8.5 meV as arising from a maximum away from the zone boundary in the dispersion curve for spin-wave modes along the chain of Ru${}^{5+}$ ions. The weaker peak near 2 meV is thought to arise from a weak interchain coupling. Our data are best reproduced using a model with three intrachain interactions and one weak interchain interaction. The experimental spin-exchange interactions are in good agreement with those calculated for a 1D model by density functional theory (DFT) methods. Furthermore, above ${T}_{N}$ we observe strong diffuse scattering at the same $Q$-position as the 5.5 meV mode, which suggests the presence of short-range magnetic correlations above ${T}_{N}$. We have estimated the correlation length \ensuremath{\xi} \ensuremath{\sim} 2.9 \AA{} at 50 K, which is close to 2.99 \AA{}, the shortest distance between the Ru${}^{5+}$ cations along the zig-zag chain.}, number={17}, journal={PHYSICAL REVIEW B}, author={Manuel, P. and Adroja, D. T. and Lindgard, Per-Anker and Hillier, A. D. and Battle, P. D. and Son, Won-Joon and Whangbo, Myung-Hwan}, year={2011}, month={Nov} } @article{kan_wu_lee_kang_whangbo_2011, title={On the High Magnetic-Ordering Temperature of the 5d Magnetic Oxide Ca3LiOsO6 Crystallizing in a Trigonal Crystal Structure: Density Functional Analysis}, volume={50}, ISSN={["0020-1669"]}, DOI={10.1021/ic200305a}, abstractNote={The 5d magnetic oxide Ca3LiOsO6 has a trigonal arrangement of its LiOsO6 chains parallel to the c-direction and hence has triangular arrangements of high-spin Os5+ (d3) ions but exhibits no spin frustration and undergoes a long-range antiferromagnetic ordering at a high temperature. The origin of this apparently puzzling observation was examined by evaluating the nearest-neighbor Os−O···O−Os spin exchange interactions of Ca3LiOsO6 on the basis of density functional calculations. Our study shows that, of the two nearest-neighbor interchain spin exchanges, one dominates over the other and that the intrachain spin exchange and the dominating interchain spin exchange are strong and form a three-dimensional antiferromagnetic spin lattice with no spin frustration, which is responsible for the long-range antiferromagnetic ordering of Ca3LiOsO6 at high temperature. In determining the strengths of the Os−O···O−Os exchange interactions of Ca3LiOsO6, the Li+ and Ca2+ ions of the O···Li+···O and O···Ca2+···O linkages are found to play only a minor role.}, number={9}, journal={INORGANIC CHEMISTRY}, author={Kan, Erjun and Wu, Fang and Lee, Changhoon and Kang, Jinhee and Whangbo, Myung-Hwan}, year={2011}, month={May}, pages={4182–4186} } @article{tian_wibowo_loye_whangbo_2011, title={On the Magnetic Insulating States, Spin Frustration, and Dominant Spin Exchange of the Ordered Double-Perovskites Sr2CuOsO6 and Sr2NiOsO6: Density Functional Analysis}, volume={50}, ISSN={["1520-510X"]}, DOI={10.1021/ic200167j}, abstractNote={The ordered double-perovskites Sr(2)MOsO(6) (M = Cu, Ni) consisting of 3d and 5d transition-metal magnetic ions (M(2+) and Os(6+), respectively) are magnetic insulators; the magnetic susceptibilities of Sr(2)CuOsO(6) and Sr(2)NiOsO(6) obey the Curie-Weiss law with dominant antiferromagnetic and ferromagnetic interactions, respectively, and the zero-field-cooled and field-cooled susceptibility curves of both compounds diverge below ∼20 K. In contrast, the available density functional studies predicted both Sr(2)CuOsO(6) and Sr(2)NiOsO(6) to be metals. We resolved this discrepancy on the basis of systematic density functional calculations. The magnetic insulating states of Sr(2)MOsO(6) are found only when a substantially large on-site repulsion is employed for the Os atom, although it is a 5d element. The cause for the divergence between the zero-field-cooled and field-cooled susceptibility curves in both compounds and the reason for the difference in their dominant magnetic interactions were investigated by examining their spin exchange interactions.}, number={9}, journal={INORGANIC CHEMISTRY}, author={Tian, Chuan and Wibowo, Arief C. and Loye, Hans-Conrad Zur and Whangbo, Myung-Hwan}, year={2011}, month={May}, pages={4142–4148} } @article{koo_lee_whangbo_mcintyre_kremer_2011, title={On the Nature of the Spin Frustration in the CuO2 Ribbon Chains of LiCuVO4: Crystal Structure Determination at 1.6 K, Magnetic Susceptibility Analysis, and Density Functional Evaluation of the Spin Exchange Constants}, volume={50}, ISSN={["1520-510X"]}, DOI={10.1021/ic102518t}, abstractNote={The spin-1/2 Cu(2+) ions of LiCuVO(4) form one-dimensional chains along the b direction, and the spin frustration in LiCuVO(4) is described in terms of the nearest-neighbor ferromagnetic exchange J(1) and the next-nearest-neighbor antiferromagnetic exchange J(2) in these chains. Recently, it has become controversial whether or not J(1) is stronger in magnitude than J(2). To resolve this controversy, we determined the crystal structure of LiCuVO(4) at 1.6 K by neutron diffraction, analyzed the magnetic susceptibility of LiCuVO(4) to deduce the Curie-Weiss temperature θ and the J(2)/J(1) ratio, and finally extracted the spin exchange constants of LiCuVO(4) on the basis of density functional calculations. Our work shows unambiguously that the Curie-Weiss temperature θ of LiCuVO(4) is negative in the range of -20 K, so that J(2) is substantially stronger in magnitude than J(1).}, number={8}, journal={INORGANIC CHEMISTRY}, author={Koo, Hyun-Joo and Lee, Changhoon and Whangbo, Myung-Hwan and McIntyre, Garry J. and Kremer, Reinhard K.}, year={2011}, month={Apr}, pages={3582–3588} } @article{xiang_kan_wei_whangbo_gong_2011, title={Predicting the spin-lattice order of frustrated systems from first principles}, volume={84}, ISSN={["1098-0121"]}, DOI={10.1103/physrevb.84.224429}, abstractNote={A novel general method of describing the spin-lattice interactions in magnetic solids was proposed in terms of first principles calculations. The spin exchange and Dzyaloshinskii-Moriya interactions as well as their derivatives with respect to atomic displacements can be evaluated efficiently on the basis of density functional calculations for four ordered spin states. By taking into consideration the spin-spin interactions, the phonons, and the coupling between them, we show that the ground state structure of a representative spin-frustrated spinel, MgCr2 O4, is tetragonally distorted, in agreement with experiments. However, our calculations find the lowest energy for the collinear spin ground state, in contrast to previously suggested non-collinear models.}, number={22}, journal={PHYSICAL REVIEW B}, author={Xiang, H. J. and Kan, E. J. and Wei, Su-Huai and Whangbo, M. -H. and Gong, X. G.}, year={2011}, month={Dec} } @article{musfeldt_liu_li_kang_lee_jena_manson_schlueter_carr_whangbo_2011, title={Pressure-Induced Local Structure Distortions in Cu(pyz)F-2(H2O)(2)}, volume={50}, ISSN={["1520-510X"]}, DOI={10.1021/ic2008039}, abstractNote={We employed infrared spectroscopy along with complementary lattice dynamics and spin density calculations to investigate pressure-driven local structure distortions in the copper coordination polymer Cu(pyz)F(2)(H(2)O)(2). Here, pyz is pyrazine. Our study reveals rich and fully reversible local lattice distortions that buckle the pyrazine ring, disrupt the bc-plane O-H···F hydrogen-bonding network, and reinforce magnetic property switching. The resiliency of the soft organic ring is a major factor in the stability of this material. Interestingly, the collective character of the lattice vibrations masks direct information on the Cu-N and Cu-O linkages through the series of pressure-induced Jahn-Teller axis switching transitions, although Cu-F bond softening is clearly identified above 3 GPa. These findings illustrate the importance of combined bulk and local probe techniques for microscopic structure determination in complex materials.}, number={13}, journal={INORGANIC CHEMISTRY}, author={Musfeldt, J. L. and Liu, Z. and Li, S. and Kang, J. and Lee, C. and Jena, P. and Manson, J. L. and Schlueter, J. A. and Carr, G. L. and Whangbo, M. -H.}, year={2011}, month={Jul}, pages={6347–6352} } @article{law_reuvekamp_glaum_lee_kang_whangbo_kremer_2011, title={Quasi-one-dimensional antiferromagnetism and multiferroicity in CuCrO4}, volume={84}, ISSN={["1098-0121"]}, DOI={10.1103/physrevb.84.014426}, abstractNote={The bulk magnetic properties of the new quasi-one-dimensional Heisenberg antiferromagnet, CuCrO${}_{4}$, were characterized by magnetic susceptibility, heat capacity, optical spectroscopy, electron paramagnetic resonance and dielectric capacitance measurements, and density functional evaluations of the intrachain and interchain spin-exchange interactions. We found type-II multiferroicity below the N\'eel temperature of 8.2(5) K, arising from competing antiferromagnetic nearest-neighbor (${J}_{\mathrm{nn}}$) and next-nearest-neighbor (${J}_{\mathrm{nnn}}$) intrachain spin-exchange interactions. Experimental and theoretical results indicate that the ratio ${J}_{\mathrm{nn}}$/${J}_{\mathrm{nnn}}$ is close to 2, putting CuCrO${}_{4}$ in the vicinity of the Majumdar-Ghosh point.}, number={1}, journal={PHYSICAL REVIEW B}, author={Law, J. M. and Reuvekamp, P. and Glaum, R. and Lee, C. and Kang, J. and Whangbo, M. -H. and Kremer, R. K.}, year={2011}, month={Jul} } @article{xiang_kan_whangbo_lee_wei_gong_2011, title={Single-ion anisotropy, Dzyaloshinskii-Moriya interaction, and negative magnetoresistance the spin-1/2 pyrochlore R2V2O7}, volume={83}, ISSN={["2469-9969"]}, DOI={10.1103/physrevb.83.174402}, abstractNote={The electronic and magnetic properties of spin-1/2 pyrochlores $R$${}_{2}$V${}_{2}$O${}_{7}$ were investigated on the basis of density-functional calculations. Contrary to common belief, the spin-1/2 ${\text{V}}^{4+}$ ions are found to have a substantial easy-axis single-ion anisotropy. We show that the magnon quantum Hall effect of Lu${}_{2}$V${}_{2}$O${}_{7}$ is a combined consequence of the easy-axis single-ion anisotropy and the Dzyaloshinskii-Moriya interaction of the spin-1/2 ${\text{V}}^{4+}$ ions. We also show that the negative magnetoresistance observed for $R$${}_{2}$V${}_{2}$O${}_{7}$ arises from a different mechanism, i.e., the band gap decreases as the spin alignment becomes more parallel to each other.}, number={17}, journal={PHYSICAL REVIEW B}, author={Xiang, H. J. and Kan, E. J. and Whangbo, M. -H. and Lee, C. and Wei, Su-Huai and Gong, X. G.}, year={2011}, month={May} } @article{law_hoch_glaum_heinmaa_stern_kang_lee_whangbo_kremer_2011, title={Spin-Peierls transition in the S=1/2 compound TiPO4 featuring large intrachain coupling}, volume={83}, ISSN={["1098-0121"]}, DOI={10.1103/physrevb.83.180414}, abstractNote={We investigated the magnetic and structural properties of the quasi-one-dimensional 3${d}^{1}$ quantum chain system TiPO${}_{4}$ ($J~$ 965 K) by magnetic susceptibility, heat capacity, electron spin resonance, x-ray diffraction, and nuclear magnetic resonance (NMR) measurements, and by density functional theory (DFT) calculations. TiPO${}_{4}$ undergoes two magnetostructural phase transitions, one at 111 K and the other at 74 K. Below 74 K, NMR detects two different $^{31}\mathrm{P}$ signals and the magnetic susceptibility vanishes, while DFT calculations evidence a bond alternation of the Ti-Ti distances within each chain. Thus, the 74 K phase transition is a spin-Peierls transition which evolves from an incommensurate phase existing between 111 and 74 K.}, number={18}, journal={PHYSICAL REVIEW B}, author={Law, J. M. and Hoch, C. and Glaum, R. and Heinmaa, I. and Stern, R. and Kang, J. and Lee, C. and Whangbo, M. -H. and Kremer, R. K.}, year={2011}, month={May} } @article{manson_lapidus_stephens_peterson_carreiro_southerland_lancaster_blundell_steele_goddard_et al._2011, title={Structural, Electronic, and Magnetic Properties of Quasi-1D Quantum Magnets [Ni(HF2)(pyz)(2)]X (pyz = pyrazine; X = PF6-, SbF6-) Exhibiting Ni-FHF-Ni and Ni-pyz-Ni Spin Interactions}, volume={50}, ISSN={["1520-510X"]}, DOI={10.1021/ic102532h}, abstractNote={[Ni(HF(2))(pyz)(2)]X {pyz = pyrazine; X = PF(6)(-) (1), SbF(6)(-) (2)} were structurally characterized by synchrotron X-ray powder diffraction and found to possess axially compressed NiN(4)F(2) octahedra. At 298 K, 1 is monoclinic (C2/c) with unit cell parameters, a = 9.9481(3), b = 9.9421(3), c = 12.5953(4) Å, and β = 81.610(3)° while 2 is tetragonal (P4/nmm) with a = b = 9.9359(3) and c = 6.4471(2) Å and is isomorphic with the Cu-analogue. Infinite one-dimensional (1D) Ni-FHF-Ni chains propagate along the c-axis which are linked via μ-pyz bridges in the ab-plane to afford three-dimensional polymeric frameworks with PF(6)(-) and SbF(6)(-) counterions occupying the interior sites. A major difference between 1 and 2 is that the Ni-F-H bonds are bent (∼157°) in 1 but are linear in 2. Ligand field calculations (LFT) based on an angular overlap model (AOM), with comparison to the electronic absorption spectra, indicate greater π-donation of the HF(2)(-) ligand in 1 owing to the bent Ni-F-H bonds. Magnetic susceptibility data for 1 and 2 exhibit broad maxima at 7.4 and 15 K, respectively, and λ-like peaks in dχT/dT at 6.2 and 12.2 K that are ascribed to transitions to long-range antiferromagnetic order (T(N)). Muon-spin relaxation and specific heat studies confirm these T(N)'s. A comparative analysis of χ vs T to various 1D Heisenberg/Ising models suggests moderate antiferromagnetic interactions, with the primary interaction strength determined to be 3.05/3.42 K (1) and 5.65/6.37 K (2). However, high critical fields of 19 and 37.4 T obtained from low temperature pulsed-field magnetization data indicate that a single exchange constant (J(1D)) alone is insufficient to explain the data and that residual terms in the spin Hamiltonian, which could include interchain magnetic couplings (J(⊥)), as mediated by Ni-pyz-Ni, and single-ion anisotropy (D), must be considered. While it is difficult to draw absolute conclusions regarding the magnitude (and sign) of J(⊥) and D based solely on powder data, further support offered by related Ni(II)-pyz compounds and our LFT and density-functional theory (DFT) results lead us to a consistent quasi-1D magnetic description for 1 and 2.}, number={13}, journal={INORGANIC CHEMISTRY}, author={Manson, Jamie L. and Lapidus, Saul H. and Stephens, Peter W. and Peterson, Peter K. and Carreiro, Kimberly E. and Southerland, Heather I. and Lancaster, Tom and Blundell, Stephen J. and Steele, Andrew J. and Goddard, Paul A. and et al.}, year={2011}, month={Jul}, pages={5990–6009} } @article{tang_li_mallik_zhang_clerac_yee_whangbo_mungalimane_holmes_2011, title={Synthesis and Characterization of Di- and Trivalent Pyrazolylborate beta-Diketonates and Cyanometalates}, volume={50}, ISSN={["1520-510X"]}, DOI={10.1021/ic200464t}, abstractNote={The syntheses, structures, and magnetic properties of a series of di- and trivalent hydridotris(3,5-dimethylpyrazol-1-yl)borate (Tp*) cyanomanganates are described. Treatment of tris(acetylacetonate)manganese(III) [Mn(acac)3] with KTp* and tetra(ethyl)ammonium cyanide affords [NEt4][(Tp*)MnII(κ2-acac)(CN)] (1), as the first monocyanomanganate(II) complex; attempted oxidation of 1 with iodine affords {(Tp*)MnII(κ2-acac3-CN)}n (2) as a one-dimensional chain and bimetallic {[NEt4][(Tp*)MnII(κ2-acac3-CN)]2(μ-CN) (3) as the major and minor products, respectively. A fourth complex, [NEt4][(Tp*)MnII(η2-acac3-CN)(η1-NC-acac)] (4), is obtained via treatment of Mn(acac3-CN)3 with KTp* and [NEt4]CN, while [NEt4]2[MnII(CN)4] (5) was prepared from manganese(II) trifluoromethanesulfonate and excess [NEt4]CN. Tricyanomanganate(III) complexes, [cat][(Tp*)MnIII(CN)3] [cat = NEt4+, 7; PPN+, 8], are prepared via sequential treatment of Mn(acac3-CN)3 with KTp*, followed by [NEt4]CN, or [cat]3[MnIII(CN)6] with (Tp*)SnBu2Cl. Magnetic measurements indicate that 1, 2, and 4 contain isotropic MnII (S = 5/2; g = 2.00) centers, and no long-range magnetic ordering is found above 1.8 K. Compounds 7 and 8 contain S = 1 MnIII centers that adopt singly degenerate spin ground states without orbital contributions to their magnetic moments.}, number={11}, journal={INORGANIC CHEMISTRY}, author={Tang, Minao and Li, Dongfeng and Mallik, Uma Prasad and Zhang, Yuan-Zhu and Clerac, Rodolphe and Yee, Gordon T. and Whangbo, Myung-Hwan and Mungalimane, Amshumali and Holmes, Stephen M.}, year={2011}, month={Jun}, pages={5153–5164} } @article{zheng_huang_wei_dai_whangbo_2011, title={Synthesis and optical properties of amorphous C-Si-O particles}, volume={131}, ISSN={["1872-7883"]}, DOI={10.1016/j.jlumin.2010.10.001}, abstractNote={Amorphous C–Si–O particles, prepared by pyrolyzing PDMS in a horizontal furnace using the carrier gas N2/H2 at 900 °C, were characterized by electron microscopy, X-ray diffraction, FTIR spectroscopy, X-ray photoelectron spectroscopy and fluorescence spectroscopy. The particles possess four luminescence peaks at 440, 465, 533 and 620 nm, and produce stable red, green or blue light emissions at room temperature when irradiated with appropriate wavelengths, the four peaks attribute to different defect centers in the particles. And the particles exhibit the highest photoluminescence intensity when annealed at 600 °C.}, number={2}, journal={JOURNAL OF LUMINESCENCE}, author={Zheng, Liren and Huang, Baibiao and Wei, Jiyong and Dai, Ying and Whangbo, Myung-Hwan}, year={2011}, month={Feb}, pages={218–224} } @article{manson_warter_schlueter_lancaster_steele_blundell_pratt_singleton_mcdonald_lee_et al._2011, title={[Cu(HF2)(2)(pyrazine)](n): A Rectangular Antiferromagnetic Lattice with a Spin Exchange Path Made Up of Two Different FHF- Bridges}, volume={50}, ISSN={["1521-3773"]}, DOI={10.1002/anie.201006653}, abstractNote={The two-dimensional antiferromagnet [Cu(HF2)2(pyz)]n (pyz=pyrazine) has a rectangular lattice (see picture) displaying two types of FHF− bridging modes. The spin exchange through Cu-(FHF)2-Cu is about 90 % stronger than through Cu-pyz-Cu, and the μ1,1-coordinated FHF−, which is close in nature to F−⋅⋅⋅HF, is largely responsible for the exchange. C black, Cu red, F green, H cyan. Detailed facts of importance to specialist readers are published as ”Supporting Information”. Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.}, number={7}, journal={ANGEWANDTE CHEMIE-INTERNATIONAL EDITION}, author={Manson, Jamie L. and Warter, Michelle L. and Schlueter, John A. and Lancaster, Tom and Steele, Andrew J. and Blundell, Stephen J. and Pratt, Francis L. and Singleton, John and McDonald, Ross D. and Lee, Changhoon and et al.}, year={2011}, pages={1573–1576} } @article{liu_huang_wang_qin_zhang_wei_dai_wang_whangbo_2010, title={Amino acid-assisted synthesis of ZnO twin-prisms and functional group's influence on their morphologies}, volume={507}, ISSN={["1873-4669"]}, DOI={10.1016/j.jallcom.2010.07.192}, abstractNote={ZnO twin-prisms were prepared by a simple solvothermal process with glutamic acid as surface modification agent in ethanol. Compared with the twin-cones that were obtained when glutamic acid was absent, the ZnO twin-prisms have optimized crystallinity with high symmetry, sharp crystal edges and few defects. Probable reaction mechanism between ZnO and glutamic acid was proposed based on our experimental analysis. Then it was verified by a series of comparison experiments by employing glycine, acetic acid and ethylamine as surface modification agents. Our results indicate that both alkaline and acidic groups play an important role on the formation of ZnO twin-prisms, and when either of them was absent, twin-prism structures cannot be obtained. The photoluminescence properties of as-prepared ZnO twin-prisms and twin-cones were also studied.}, number={1}, journal={JOURNAL OF ALLOYS AND COMPOUNDS}, author={Liu, Haixia and Huang, Baibiao and Wang, Zeyan and Qin, Xiaoyan and Zhang, Xiaoyang and Wei, Jiyong and Dai, Ying and Wang, Peng and Whangbo, Myung-Hwan}, year={2010}, month={Sep}, pages={326–330} } @article{lee_whangbo_koehler_2010, title={Analysis of Electronic Structures and Chemical Bonding of Metal-rich Compounds. 2. Presence of Dimer (T-T)(4-) and Isolated T2- Anions in the Polar Intermetallic Cr5B3-Type Compounds AE(5)T(3) (AE = Ca, Sr; T = Au, Ag, Hg, Cd, Zn)}, volume={636}, ISSN={["1521-3749"]}, DOI={10.1002/zaac.200900421}, abstractNote={Abstract First principles density functional calculations were carried out to probe the oxidation states of the transition‐metal and alkaline‐earth elements in the Cr 5 B 3 ‐type compounds AE 5 T 3 consisting of T 2 dimers and isolated T atoms (i.e., Ca 5 Au 3 , Ca 5 Ag 3 , Ca 5 Hg 3 , Sr 5 Cd 3 , and Ca 5 Zn 3 ). The electronic structures of all these AE 5 T 3 compounds are best described as [( AE 2+ ) 5 ( T – T ) 4– ( T 2– )]+4e – . In the covalent bonding of the AE 2+ ions with the transition metal anions T 2– , the ( n –1)d orbitals of AE 2+ contribute more than the n s and n p orbitals of AE 2+ .}, number={1}, journal={ZEITSCHRIFT FUR ANORGANISCHE UND ALLGEMEINE CHEMIE}, author={Lee, Changhoon and Whangbo, Myung-Hwan and Koehler, Juergen}, year={2010}, pages={36–40} } @article{tian_lee_kan_wu_whangbo_2010, title={Analysis of the Magnetic Structure and Ferroelectric Polarization of Monoclinic MnSb2S4 by Density Functional Theory Calculations}, volume={49}, ISSN={["1520-510X"]}, DOI={10.1021/ic101351b}, abstractNote={Monoclinic MnSb(2)S(4) consists of MnS(4) chains made up of edge-sharing MnS(6) octahedra and adopts a (0, 0.369, 0) magnetic superstructure below 25 K. This ordered magnetic structure, in which the spins of each MnS(4) chain possess a helical spin arrangement, has C(2)' symmetry. On the basis of density functional theory calculations, we explored the origin of the observed noncollinear spin arrangement of MnSb(2)S(4) by evaluating its spin exchanges to find that spin exchanges are frustrated not only within each MnS(4) chain but also between adjacent MnS(4) chains. Our analysis predicts that MnSb(2)S(4) is a multiferroic with a ferroelectric polarization of ∼14 μC/m(2) along the chain direction, and a field-induced reversal of the ferroelectric polarization of MnSb(2)S(4) can occur by reversing the direction of the helical spin rotation in each MnS(4) chain.}, number={23}, journal={INORGANIC CHEMISTRY}, author={Tian, Chuan and Lee, Changhoon and Kan, Erjun and Wu, Fang and Whangbo, Myung-Hwan}, year={2010}, month={Dec}, pages={10956–10959} } @article{mentre_kabbour_ehora_tricot_daviero-minaud_whangbo_2010, title={Anion-Vacancy-Induced Magneto-Crystalline Anisotropy in Fluorine-Doped Hexagonal Cobaltites}, volume={132}, ISSN={["1520-5126"]}, DOI={10.1021/ja100170m}, abstractNote={The two cobalt hexagonal perovskites 6H-Ba(6)Co(6)F(0.93)O(16) and 10H-Ba(5)Co(5)F(0.77)O(12.88) were prepared, and their structures were examined by X-ray and neutron diffraction and by (19)F solid state NMR spectroscopy. The magnetic and transport properties of these compounds were probed by magnetic susceptibility and electrical resistivity measurements, and their electronic structures by density functional and tight-binding calculations. The [BaOF(1-x)] layers of these compounds create corner-sharing tetrahedral Co(2)O(7) dimers at the interface between their face-sharing octahedral oligomers. Our density functional calculations leads to an unambiguous charge distribution model, which assigns high-spin Co(3+) ions for the tetrahedral sites and low-spin Co(3+)/Co(4+) ions for the octahedral sites, and this model should be valid for the parent BaCoO(3-delta) and the related oxychlorides and oxybromides as well. The F(-) vacancies in the [BaOF(1-x)] layers cause a strong distortion in the tetrahedral dimer Co(2)O(7), which in turn affects the spin orientation of the high-spin Co(3+) ions of the CoO(4) tetrahedra, i.e., parallel to the c-direction in Ba(6)Co(6)F(1-x)O(16-delta) but perpendicular to the c-direction in Ba(5)Co(5)F(1-x)O(13-delta). This difference in the spin orientations is related to the d-states of the distorted CoO(4) tetrahedra with high-spin Co(3+) (d(6)) ion on the basis of tight binding calculations and spin-orbit coupling as perturbation.}, number={13}, journal={JOURNAL OF THE AMERICAN CHEMICAL SOCIETY}, author={Mentre, Olivier and Kabbour, Houria and Ehora, Ghislaine and Tricot, Gregory and Daviero-Minaud, Sylvie and Whangbo, Myung-Hwan}, year={2010}, month={Apr}, pages={4865–4875} } @article{tong_lee_whangbo_kremer_simon_koehler_2010, title={Cooperative Jahn-Teller distortion leading to the spin-1/2 uniform antiferromagnetic chains in triclinic perovskites AgCuF3 and NaCuF3}, volume={12}, ISSN={["1293-2558"]}, DOI={10.1016/j.solidstatesciences.2009.02.028}, abstractNote={Abstract Polycrystalline samples of AgCuF 3 , isostructural with NaCuF 3 , were synthesized by solid state reaction and characterized by powder X-ray diffraction. The magnetic properties of AgCuF 3 and NaCuF 3 were examined by measuring their magnetic susceptibilities and evaluating their spin exchange interactions. The three-dimensional CuF 3 network of corner-sharing CuF 6 octahedra present in AgCuF 3 and NaCuF 3 shows a cooperative Jahn–Teller distortion such that their magnetic susceptibilities above 50 K are well described by an S = 1/2 Heisenberg uniform antiferromagnetic chain model with average spin exchange of J / k B ≈ −300 and −180 K, respectively. The relative strengths of these interactions are well reproduced by spin dimer analysis based on tight-binding calculations, but not by mapping analysis based on first principles density functional calculations.}, number={5}, journal={SOLID STATE SCIENCES}, author={Tong, J. and Lee, C. and Whangbo, M. -H. and Kremer, R. K. and Simon, A. and Koehler, J.}, year={2010}, month={May}, pages={680–684} } @article{law_hoch_whangbo_kremer_2010, title={Description of Anhydrous (Black) Dioptase as a S=1/2 Uniform Antiferromagnetic Chain System}, volume={636}, ISSN={["0044-2313"]}, DOI={10.1002/zaac.200900403}, abstractNote={Abstract The structural and magnetic properties of anhydrous (black) dioptase, CuSiO 3 , were investigated by carrying out single‐crystal X‐ray diffraction, specific heat, and magnetic susceptibility measurements as well as by performing spin dimer analysis based on extended Hückel tight‐binding calculations. Our spin dimer analysis indicates that black dioptase is a S = 1/2 uniform antiferromagnetic chain system with the interchain spin exchange weaker than the intrachain exchange by three orders of magnitude. Specific heat and magnetic susceptibility measurements show that the intrachain exchange is –174(2) K, and the interchain exchange is of the order of ~2 K. They lead to long‐range magnetic ordering at about 5 K as evidenced by a broad anomaly in the specific heat.}, number={1}, journal={ZEITSCHRIFT FUR ANORGANISCHE UND ALLGEMEINE CHEMIE}, author={Law, Joseph M. and Hoch, Constantin and Whangbo, Myung-Hwan and Kremer, Reinhard K.}, year={2010}, pages={54–61} } @article{schlueter_wiehl_park_souza_lang_koo_whangbo_2010, title={Enhanced Critical Temperature in a Dual-Layered Molecular Superconductor}, volume={132}, ISSN={["1520-5126"]}, DOI={10.1021/ja105854m}, abstractNote={Single-crystal X-ray diffraction has shown that the high-critical-temperature (T(c)) phase of the filamentary molecular superconductor (BEDT-TTF)(2)Ag(CF(3))(4)(1,1,2-trichloroethane) [BEDT-TTF = bis(ethylenedithio)tetrathiafulvalene] contains layers of BEDT-TTF radical cations with alternating κ- and α'-type packing motifs. This molecule-based superconductor with dual BEDT-TTF packing motifs has a T(c) five times higher than that of its polymorph that contains only κ-type packing.}, number={46}, journal={JOURNAL OF THE AMERICAN CHEMICAL SOCIETY}, author={Schlueter, John A. and Wiehl, Leonore and Park, Hyunsoo and Souza, Mariano and Lang, Michael and Koo, Hyun-Joo and Whangbo, Myung-Hwan}, year={2010}, month={Nov}, pages={16308–16310} } @article{kan_xiang_wu_lee_yang_whangbo_2010, title={Ferrimagnetism in zigzag graphene nanoribbons induced by main-group adatoms}, volume={96}, number={10}, journal={Applied Physics Letters}, author={Kan, E. and Xiang, H. J. and Wu, F. and Lee, C. and Yang, J. L. and Whangbo, M. H.}, year={2010} } @article{kan_xiang_lee_wu_yang_whangbo_2010, title={Ferroelectricity in Perovskites with s(0) A-Site Cations: Toward Near-Room-Temperature Multiferroics}, volume={49}, ISSN={["1433-7851"]}, DOI={10.1002/anie.200905997}, abstractNote={The origin of the ferroelectricity in the indium-based multiferroic perovskites (In1−xMx)MO3 (M=Mn0.5Fe0.5), and the question of how to lower their magnetic ordering (TN) and the ferroelectric Curie temperatures, was investigated by density functional calculations. The analyses explain why TN is near room temperature and why the perovskites with s0 and s2 A-site cations have similar ferroelectric distortions. Magnetic ferroelectric (FE) materials (that is, multiferroics) have received much attention and can have wide technological applications owing to the possibility of controlling their electric properties and their magnetic properties by electric fields.1, 2 An important class of multiferroic and FE3 materials is based on perovskites, ABO3, with two different cations A and B (for example A2+ and B4+ or A3+ and B3+), in which corner-sharing BO6 octahedra form the three-dimensional lattice with every B8 cube containing one A cation. An ideal cubic perovskite, in which the B-OB bonds are linear with A located at the center of each B8 cube (thus forming a AO12 polyhedron), is expected when the tolerance factor τ=(rO+rA)/(rO+rB) is unity (rA and rB are the ionic radii of the A and B cations, respectively, with rO as that of the O2− anion). In most cases, the A cations are small, so that τ<1 and the AO bonds are too long to maintain the ideal cubic structure. Consequently, the A cation moves away from the center of the B8 cube, which is accompanied by the bending of the B-O-B bonds and the rotation of the BO6 octahedra to form a lower-coordinate AOn polyhedron (n<12) with short AO bonds. The distortion of the ideal cubic perovskite toward a non-centrosymmetric FE structure requires another local instability apart from τ<1, namely, the second-order Jahn–Teller (SOJT) instability4–6 of the A-site and/or B-site cation. As found for PbTiO3,7 PbVO3,8 and BiCoO3,9 moving the A cation toward the center of one B4 face (Figure 1 a) leads to a tetragonal FE structure with space group P4mm. The B cations move away from the approaching A cations such that the coordinate environment of each B cation is more like a BO5 square pyramid with shortened axial BO bond. In PbTiO3, PbVO3, and BiCoO3, the s2 A-site cations Pb2+ and Bi3+ are susceptible to a SOJT distortion, which mixes the empty 6p orbital of A into the filled 6s2 orbital of A hence forming a lone pair on A.4 In PbTiO3, the B-site cation Ti4+ (d0) is also susceptible to a SOJT distortion, which mixes the empty Ti 3d orbitals into the filled 2p orbitals of the oxygen atom of the axial TiO bond.5, 6 Thus, in PbTiO3, the need to make short PbO bonds and the SOJT instabilities of both Pb2+ and Ti4+ ions cooperate to give rise to the observed FE distortion.10, 11 Perspective views of the local structures around the A cation in three perovskites ABO3, where the large, medium, and small circles refer to the A, B, and O atoms, respectively. a) The FE distortion in ABO3 with space group P4mm. Only eight corner-sharing BO5 square pyramids and one A cation are shown. b) The FE distortion of ABO3 with space group R3c. For simplicity, only the two BO6 octahedra at the two corners of the B8 cube along the body-diagonal direction and the AO3 unit lying between the two octahedra are shown. The AO3 unit merges with the upper BO6 octahedron to form a distorted AO6 octahedron, which shares its face with the upper BO6 octahedron, resulting in the face-sharing octahedral dimer ABO9. c) The PE structure of ABO3 with space group Rc, by which one FE structure is converted into the other FE structure with opposite polarization. The B cation in each BO6 octahedron is located at the center of the O6 octahedron, and the AO3 unit lying at the midpoint between the two octahedra is planar. Another type of the A-cation displacement from the center of the B8 cube is the movement toward one corner of the B8 cube along the body-diagonal direction (that is, the C3 rotational axis; Figure 1 b) to form a non-centrosymmetric FE trigonal structure with space group R3c, as found for BiFeO3.12 The movement of the A cation toward one corner is equivalent to that toward the opposite corner, and the two energetically-equivalent FE structures are mutually interconverted through the centrosymmetric paraelectric (PE) trigonal structure with space group Rc (Figure 1 c).13, 14 For BiFeO3, the FE Curie temperature (TE=1123 K)15 and the three-dimensional antiferromagnetic ordering temperature (TN=650 K)16 are well above room temperature. For practical applications, it is highly desirable to find multiferroics with both TE and TN close to room temperature. Recently, Belik et al.17 have achieved a partial success toward this goal; they synthesized the indium-based multiferroics (In1−xMx)MO3 (x≈0.112-0.176; M=Mn0.5Fe0.5) that have a TN value close to room temperature; however, TE is still high (for x=0.176, TN≈270 K and TE is expected to be above 670 K, but the phase is transformed irreversibly to a corundum-type structure above 670 K). These multiferroics, which are isostructural with BiFeO3, are quite surprising in two aspects. First, magnetic ordering of a system made up of magnetic ions is generally prevented when disorder is present in the system. However, long-range magnetic ordering occurs near room temperature despite the expected disorder in the A and B sites (that is, the statistical distribution of high-spin Mn3+ and Fe3+ cations). Second, it is believed that the strong FE distortion in perovskites with s2 A-site cations, such as BiFeO3, PbTiO3, PbVO3, and BiCoO3, arises from the need to create space for the lone pair on A. However, a strong FE distortion that is almost as strong as found for BiFeO3 occurs in the indium-based multiferroics, although the A-site cations (In3+, Mn3+, and Fe3+) do not possess a lone pair. Herein, we explore these puzzling observations on the basis of systematic density functional calculations for BiFeO3 and model perovskites ABO3 (A=Ga, In, Tl; B=Mn, Fe, Mn0.5Fe0.5) that simulate the indium-based multiferroics (In1−xMx)MO3. Unless stated otherwise, our calculations were carried out for the antiferromagnetic (AFM) states of ABO3 (A=Ga, In, Tl; B=Mn, Fe, Mn0.5Fe0.5) and BiFeO3 in which all nearest-neighbor (NN) spins of the B-site cations are antiferromagnetically coupled. In the hexagonal setting of the trigonal space group R3c, a unit cell of these compounds has six layers of B cations perpendicular to the c axis. To simulate the random arrangement of the Mn3+ and Fe3+ ions in A(Mn0.5Fe0.5)O3, we adopted the ordered arrangement in which layers of Mn3+ ions alternate with layers of Fe3+ ions along the c direction. This arrangement is statistically most probable because each B8 cube is given by Mn4Fe4 such that all NN cations are different. In our GGA+U calculations for the FE structures of ABO3 (A=Ga, In, Tl; B=Mn, Fe, Mn0.5Fe0.5) and BiFeO3 (with space group R3c), the positions of the atoms were fully optimized but the cell parameters were kept constant at the experimental values. The cell parameters of ABO3 (A=Ga, In, Tl; B=Mn, Fe, Mn0.5Fe0.5) were fixed at those found for (In1−xMx)MO3 (x≈0.176; M=Mn0.5Fe0.5).17 The results of our structure optimizations for the FE structures of ABO3 are summarized in terms of the three parameters ΔrA, ΔzA and ΔzB (Figure 1 b), where ΔrA is the A-cation displacement from the center of the B8 cube to the actual position of A in the B8 cube; the strength of the AO6 (BO6) octahedron distortion is measured by the displacement ΔzA (ΔzB) from the center of the O6 octahedron to the actual position of the A (B) cation. Given that the z axis taken along the c direction of the hexagonal setting (i.e., the body-diagonal direction of the B8 cube; Figure 1 b) shows that ΔzA<0 and ΔzB>0. The values of ΔrA are summarized in Table 1, and the ΔzA and ΔzB values are given in Table 2. The ΔrA values are substantial, and are largely determined by the A cation. For a given ABO3 series and BiFeO3, the ΔrA values decrease in the order Ga3+>In3+>Tl3+>Bi3+, which reflects that the A-cation size increases in the order Ga3+