@article{jana_gabilondo_mcguigan_maggard_2024, title={Syntheses, Crystal Structures, and Electronic Structures of Quaternary Group IV-Selenide Semiconductors}, volume={3}, ISSN={["1520-510X"]}, DOI={10.1021/acs.inorgchem.4c00363}, abstractNote={Early transition-metal chalcogenides have garnered recent attention for their optoelectronic properties for solar energy conversion. Herein, the first Zr-/Hf-chalcogenides with a main group cation, Ba9Hf3Sn2Se19 (1) and Ba8Zr2SnSe13(Se2) (2), have been synthesized. The structure of 1 is formed from isolated SnSe44- tetrahedra and distorted HfSe6 octahedra. The latter condense via face-sharing trimeric motifs that are further vertex-bridged into chains of 1∞[Hf(1)2Hf(2)Se11]10-. The structure of 2 is comprised of SnSe44- tetrahedra, Se22- dimers, and face-sharing dimers of distorted ZrSe6 octahedra. These represent the first reported examples of Hf-/Zr-chalcogenides exhibiting face-sharing octahedra with relatively short Hf-Hf and Zr-Zr distances. Their preparation in high purity is inhibited by their low thermodynamic stability, with calculations showing small calculated ΔUdec values of +7 and +9 meV atom-1 for 1 and 2, respectively. Diffuse reflectance measurements confirm the semiconducting nature of 1 with an indirect band gap of ∼1.4(1) eV. Electronic structure calculations show that the band gap absorptions arise from transitions between predominantly Se-4p valence bands and mixed Hf-5d/Sn-5p or Zr-4d/Sn-5p conduction bands. Optical absorption coefficients were calculated to be more than ∼105 cm-1 at greater than 1.8 eV. Thus, promising optical properties are demonstrated for solar energy conversion within these synthetically challenging chemical systems.}, journal={INORGANIC CHEMISTRY}, author={Jana, Subhendu and Gabilondo, Eric and McGuigan, Scott and Maggard, Paul A.}, year={2024}, month={Mar} }
 @article{jana_gabilondo_maggard_2024, title={Two new multinary chalcogenides with (Se<sub>2</sub>)<SUP>2-</SUP> dimers: Ba<sub>8</sub>Hf<sub>2</sub>Se<sub>11</sub>(Se<sub>2</sub>) and Ba<sub>9</sub>Hf<sub>3</sub>Se<sub>14</sub>(Se<sub>2</sub>)}, volume={329}, ISSN={["1095-726X"]}, DOI={10.1016/j.jssc.2023.124376}, abstractNote={Two multinary selenides, Ba8Hf2Se11(Se2) and Ba9Hf3Se14(Se2), with unprecedented structure types have been prepared using high-temperature synthesis techniques and represent the first known compounds in the Ba-Hf-Se system. Their structures were determined from single crystal X-ray diffraction (XRD) data. The Ba8Hf2Se11(Se2) compound crystallizes in the monoclinic C2/c space group with a = 12.3962(15) Å, b = 12.8928(15) Å, c = 18.1768(17) Å, and β = 90.685(4)º, while Ba9Hf3Se14(Se2) forms in the rhombohedral R 3¯ space group with a = b = 19.4907(6) Å and c = 23.6407(11) Å. Both have pseudo-zero-dimensional structures with homoatomic Se–Se bonding in the form of (Se2)2− at distances of 2.400–2.402 Å. The structure of Ba8Hf2Se11(Se2) is comprised of [Hf2Se11]14−, Ba2+, and (Se2)2− dimers. Conversely, the Ba9Hf3Se14(Se2) structure contains a novel perovskite-type cluster constructed from eight octahedrally-coordinated Hf cations, i.e., [Hf8Se36]40−, and isolated [HfSe6]8− units which are separated by (Se2)2− dimers and Ba2+ cations. Polycrystalline Ba8Hf2Se11(Se2) is synthesized at 1073 K using a two-step solid-state synthesis method, with the co-formation of a small amount of BaSe secondary phase. A direct bandgap of 2.2(2) eV is obtained for the polycrystalline sample of Ba8Hf2Se11(Se2), which is consistent with its yellow color. Density functional theory calculations reveal their bandgap transitions stem from predominantly filled Se-4p to empty Hf-5d at the edges of the valence bands (VB) and conduction bands (CB), respectively. The optical absorption coefficients are calculated to be large, exceeding ∼105 cm−1 at about >2.0 eV with effective masses in the CB varying from ∼0.5 me (Γ → A) in Ba8Hf2Se11(Se2) to ∼1.0 me (Γ → L) in Ba9Hf3Se14(Se2). Thus, their optoelectronic properties are shown to be competitive with existing perovskite-type chalcogenides that have been a focus of recent research efforts.}, journal={JOURNAL OF SOLID STATE CHEMISTRY}, author={Jana, Subhendu and Gabilondo, Eric A. and Maggard, Paul A.}, year={2024}, month={Jan} }
 @article{o'donnell_gabilondo_jana_koldemir_block_whangbo_kremer_pottgen_maggard_2023, title={Cation exchange route to a Eu(II)-containing tantalum oxide}, volume={328}, ISSN={["1095-726X"]}, DOI={10.1016/j.jssc.2023.124338}, abstractNote={Traditional synthetic efforts to prepare Eu(II)-containing oxides have principally involved the use of high temperature reactions starting from EuO or a controlled, highly-reducing, atmosphere. Conversely, chimie douce approaches that are more amenable to the targeted syntheses of new, and potentially metastable, Eu(II)-oxides have yet to be explored. Herein, a cation-exchange route to new Eu(II)-containing oxides, e.g., EuTa4-xO11 (x = 0.04), has been discovered and its structure determined by powder X-ray diffraction (Space group P6322 (#182), a = 6.2539(2) Å; c = 12.3417(2) Å). The compound derives from the cation exchange of Na2Ta4O11, via a reaction with EuBr2 at 1173 K, and replacement by half the number of divalent Eu cations. Rietveld refinements show preferential ordering of the Eu cations over one of the two possible cation sites, i.e., Wyckoff site 2d (∼94%; Eu1) versus 2b (∼6%; Eu2). Total energy calculations confirm an energetic preference of the Eu cation in the 2d site. Tantalum vacancies of ∼1% occur within the layer of Eu cations and TaO6 octahedra, and ∼20% partial oxidation of Eu(II) to Eu(III) cations from charge balance considerations. 151Eu Mössbauer spectroscopy measured at 78 K found a Eu(II):Eu(III) ratio of 69:31, with a relatively broad line width of the former signal of Γ = 7.6(2) mm s–1. Also, the temperature-dependent magnetic susceptibility could be fitted to a Curie Weiss expression, giving a μeff = 6.2 μB and θCW = −10 K and confirming a mixture of Eu(II)/Eu(III) cations. The optical bandgap of EuTa4-xO11 was found to be ∼1.5 eV (indirect), significantly redshifted as compared to ∼4.1 eV for Na2Ta4O11. Spin-polarized electronic structure calculations show that this redshift stems from the addition of Eu 4f7 states as a higher-energy valence band. Thus, these results demonstrate a new cation-exchange approach that represents a useful synthetic pathway to new Eu(II)-containing oxides for tunable magnetic and optical properties.}, journal={JOURNAL OF SOLID STATE CHEMISTRY}, author={O'Donnell, Shaun and Gabilondo, Eric and Jana, Subhendu and Koldemir, Aylin and Block, Theresa and Whangbo, Myung-Hwan and Kremer, Reinhard and Pottgen, Rainer and Maggard, Paul A.}, year={2023}, month={Dec} }