@article{sohag_o'donnell_fuoco_maggard_2021, title={A Metastable p-Type Semiconductor as a Defect-Tolerant Photoelectrode}, volume={26}, ISSN={["1420-3049"]}, url={https://www.mdpi.com/1420-3049/26/22/6830}, DOI={10.3390/molecules26226830}, abstractNote={A p-type Cu3Ta7O19 semiconductor was synthesized using a CuCl flux-based approach and investigated for its crystalline structure and photoelectrochemical properties. The semiconductor was found to be metastable, i.e., thermodynamically unstable, and to slowly oxidize at its surfaces upon heating in air, yielding CuO as nano-sized islands. However, the bulk crystalline structure was maintained, with up to 50% Cu(I)-vacancies and a concomitant oxidation of the Cu(I) to Cu(II) cations within the structure. Thermogravimetric and magnetic susceptibility measurements showed the formation of increasing amounts of Cu(II) cations, according to the following reaction: Cu3Ta7O19 + x/2 O2 → Cu(3−x)Ta7O19 + x CuO (surface) (x = 0 to ~0.8). With minor amounts of surface oxidation, the cathodic photocurrents of the polycrystalline films increase significantly, from <0.1 mA cm−2 up to >0.5 mA cm−2, under visible-light irradiation (pH = 6.3; irradiant powder density of ~500 mW cm−2) at an applied bias of −0.6 V vs. SCE. Electronic structure calculations revealed that its defect tolerance arises from the antibonding nature of its valence band edge, with the formation of defect states in resonance with the valence band, rather than as mid-gap states that function as recombination centers. Thus, the metastable Cu(I)-containing semiconductor was demonstrated to possess a high defect tolerance, which facilitates its high cathodic photocurrents.}, number={22}, journal={MOLECULES}, author={Sohag, Zahirul and O'Donnell, Shaun and Fuoco, Lindsay and Maggard, Paul A.}, year={2021}, month={Nov} }
 @article{king_sahoo_fuoco_stuart_dougherty_liu_maggard_2014, title={Copper Deficiency in the p-Type Semiconductor Cu1–xNb3O8}, volume={26}, ISSN={0897-4756 1520-5002}, url={http://dx.doi.org/10.1021/CM404147J}, DOI={10.1021/cm404147j}, abstractNote={The p-type semiconductor CuNb3O8 has been synthesized by solid-state and flux reactions and investigated for the effects of copper extrusion from its structure at 250–750 °C in air. High purity CuNb3O8 could be prepared by solid-state reactions at 750 °C at reaction times of 15 min and 48 h, and within a CuCl flux (10:1 molar ratio) at 750 °C at reaction times of 15 min and 12 h. The CuNb3O8 phase grows rapidly into well-faceted micrometer-sized crystals under these conditions, even with the use of Cu2O and Nb2O5 nanoparticle reactants. Heating CuNb3O8 in air to 450 °C for 3 h yields Cu-deficient Cu0.79(2)Nb3O8 that was characterized by powder X-ray Rietveld refinements (Sp. Grp. P21/a, Z = 4, a = 15.322(2) A, b = 5.0476(6) A, c = 7.4930(6) A, β = 107.07(1)o, and V = 554.0(1) A3). The parent structure of CuNb3O8 is maintained with ∼21% copper vacancies but with notably shorter Cu–O distances (by 0.16–0.27 A) within the Cu–O–Nb1 zigzag chains down its b-axis. Copper is extruded at high temperatures in air ...}, number={6}, journal={Chemistry of Materials}, publisher={American Chemical Society (ACS)}, author={King, Nacole and Sahoo, Prangya Parimita and Fuoco, Lindsay and Stuart, Sean and Dougherty, Daniel and Liu, Yi and Maggard, Paul A.}, year={2014}, month={Mar}, pages={2095–2104} }
 @article{sullivan_sahoo_fuoco_hewitt_stuart_dougherty_maggard_2014, title={Cu-Deficiency in the p-Type Semiconductor Cu5–xTa11O30: Impact on Its Crystalline Structure, Surfaces, and Photoelectrochemical Properties}, volume={26}, ISSN={0897-4756 1520-5002}, url={http://dx.doi.org/10.1021/CM502891T}, DOI={10.1021/cm502891t}, abstractNote={The p-type semiconductor Cu5Ta11O30 has been investigated for the effect of Cu extrusion on its crystalline structure, surface chemistry, and photoelectrochemical properties. The Cu5Ta11O30 phase was prepared in high purity using a CuCl-mediated flux synthesis route, followed by heating the products in air from 250 to 750 °C in order to investigate the effects of its reported film preparation conditions as a p-type photoelectrode. At 650 °C and higher temperatures, Cu5Ta11O30 is found to decompose into CuTa2O6 and Ta2O5. At lower temperatures of 250 to 550 °C, nanosized CuIIO surface islands and a Cu-deficient Cu5–xTa11O30 crystalline structure (i.e., x ∼ 1.8(1) after 450 °C for 3 h in air) is found by electron microscopy and Rietveld structural refinement results, respectively. Its crystalline structure exhibits a decrease in the unit cell volume with increasing reaction temperature and time, owing to the increasing removal of Cu(I) ions from its structure. The parent structure of Cu5Ta11O30 is conserved...}, number={23}, journal={Chemistry of Materials}, publisher={American Chemical Society (ACS)}, author={Sullivan, Ian and Sahoo, Prangya P. and Fuoco, Lindsay and Hewitt, Andrew S. and Stuart, Sean and Dougherty, Daniel and Maggard, Paul A.}, year={2014}, month={Nov}, pages={6711–6721} }
 @article{mclamb_sahoo_fuoco_maggard_2013, title={Flux Growth of Single-Crystal Na2Ta4O11 Particles and their Photocatalytic Hydrogen Production}, volume={13}, ISSN={["1528-7483"]}, DOI={10.1021/cg301859d}, abstractNote={Single-crystal particles of the layered natrotantite, i.e., Na2Ta4O11, were prepared within a K2SO4/Na2SO4 flux for flux-to-reactant molar ratios from 12:1 to 1:1 at a reaction temperature of 1000 °C for 2 h. Depending on the conditions, the flux reactions yielded crystals of Na2Ta4O11 that ranged in size from ∼100 nm to ∼1000 nm. The highest and lowest flux amounts yielded more isolated single crystals with sharper facets and surfaces, whereas intermediate flux amounts yielded more aggregates of particles with smooth and rounded surface features. All products were characterized by UV–vis diffuse reflectance techniques and were found to exhibit an indirect bandgap size of ∼4.1–4.3 eV and a larger direct bandgap transition of ∼4.5 eV. When the crystals are suspended in aqueous solutions and irradiated by ultraviolet light, they exhibit stable photocatalytic rates for hydrogen production of ∼13.4 μmol of H2·g–1·h–1 to ∼34.1 μmol of H2·g–1·h–1. The higher photocatalytic rates are found for the single crystal...}, number={6}, journal={CRYSTAL GROWTH & DESIGN}, author={McLamb, Nathan and Sahoo, Prangya Parimita and Fuoco, Lindsay and Maggard, Paul A.}, year={2013}, month={Jun}, pages={2322–2326} }
 @article{arney_fuoco_boltersdorf_maggard_2013, title={Flux Synthesis of Na2Ca2Nb4O13: The Influence of Particle Shapes, Surface Features, and Surface Areas on Photocatalytic Hydrogen Production}, volume={96}, ISSN={["0002-7820"]}, DOI={10.1111/jace.12122}, abstractNote={The layered perovskite (n = 4) Ruddlesden‐Popper phase Na2Ca2Nb4O13 was prepared within molten NaCl and Na2SO4 fluxes, yielding either rod‐shaped or platelet‐shaped particles, respectively. The flux‐to‐reactant molar ratios of 5:1 or 20:1 were found to significantly influence particle sizes and surface areas, while still maintaining the overall particle shapes. Measured surface areas of flux‐prepared Na2Ca2Nb4O13 particles ranged from ∼0.36 to 4.6 m2/g, with the highest surface areas obtained using a 5:1 (NaCl‐to‐Na2Ca2Nb4O13) molar ratio. All samples exhibited a bandgap size of ∼3.3 eV, as determined by UV–Vis diffuse reflectance measurements. Photocatalytic rates for hydrogen production under ultraviolet light for platinized Na2Ca2Nb4O13 particles in an aqueous methanol solution ranged from ∼230 to 1355 μmol H2 g−1 h−1 when using the photochemical deposition (PCD) method of platinization, and ∼113–1099 μmol H2 g−1 h−1 when using the incipient wetness impregnation (IWI) method of platinization. The higher photocatalytic rates were obtained for the rod‐shaped particles with the highest surface areas, with an apparent quantum yield (AQY) measured at ∼6.5% at 350 nm. For the platelet‐shaped particles, the higher photocatalytic rates were observed for the sample with the lowest surface area but the largest concentration of stepped edges and grooves observed at the particle surfaces. The latter origin of the photocatalytic activity is confirmed by the significant enhancement of the photocatalytic rates by the PCD method that allows for the preferential deposition of the surface Pt cocatalyst islands at the stepped edges and grooves, while the photocatalytic enhancement is much smaller when using the more general IWI platinization method.}, number={4}, journal={JOURNAL OF THE AMERICAN CERAMIC SOCIETY}, author={Arney, David and Fuoco, Lindsay and Boltersdorf, Jonathan and Maggard, Paul A.}, year={2013}, month={Apr}, pages={1158–1162} }
 @article{fuoco_joshi_maggard_2012, title={Preparation and Photoelectrochemical Properties of p-type Cu5Ta11O30 and Cu3Ta7O19 Semiconducting Polycrystalline Films}, volume={116}, ISSN={["1932-7447"]}, DOI={10.1021/jp300267v}, abstractNote={New p-type polycrystalline films of semiconducting Cu5Ta11O30 and Cu3Ta7O19 were prepared on fluorine-doped tin oxide (FTO) glass starting from their CuCl-flux synthesis as highly faceted micrometer-sized particles. The particles were annealed on FTO at 400–500 °C, followed by a mild oxidation in air at between 250 and 550 °C. In an aqueous 0.5 M Na2SO4 electrolyte solution (pH = 6.3), the films exhibit strong cathodic photocurrents under irradiation by visible and/or ultraviolet light, which increased with higher annealing and oxidation temperatures owing to increased p-type carrier concentration and better electrical contact between particles. Thermogravimetric analyses show that the oxidation treatments result in an oxygen uptake at concentrations of ∼3 × 1020 cm–3 at 250 °C, to ∼4 × 1021 cm–3 at 550 °C, with the higher temperatures leading to the decomposition of the film. The Cu5Ta11O30 and Cu3Ta7O19 bulk powders exhibit band-gap sizes of ∼2.59 and ∼2.47 eV, respectively, and show an onset of their c...}, number={19}, journal={JOURNAL OF PHYSICAL CHEMISTRY C}, author={Fuoco, Lindsay and Joshi, Upendra A. and Maggard, Paul A.}, year={2012}, month={May}, pages={10490–10497} }
 @article{fuoco_rodriguez_peppel_maggard_2011, title={Molten-Salt-Mediated Syntheses of Sr2FeReO6, Ba2FeReO6, and Sr2CrReO6: Particle Sizes, B/B ' Site Disorder, and Magnetic Properties}, volume={23}, ISSN={["1520-5002"]}, DOI={10.1021/cm202545z}, abstractNote={The half-metallic double-perovskites Sr2FeReO6, Ba2FeReO6, and Sr2CrReO6 were synthesized in high purity and homogeneity using a NaCl/KCl molten flux at 750–800 °C in as little as 3–6 h. The partic...}, number={24}, journal={CHEMISTRY OF MATERIALS}, author={Fuoco, Lindsay and Rodriguez, Dianny and Peppel, Tim and Maggard, Paul A.}, year={2011}, month={Dec}, pages={5409–5414} }