Browsing by Author "Murakami, T"
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- ItemHigh proton conductivity in Ba5Er2Al2ZrO13, a hexagonal perovskite-related oxide with intrinsically oxygen-deficient layers(American Chemical Society, 2020-05-15) Murakami, T; Hester, JR; Yashima, MFor the development of proton-based electrolytes, high proton conductivity at intermediate temperatures (300–600 °C) is crucial, but the available materials have been confined to a limited number of the structure families, such as cubic perovskites. Herein, we report Ba5Er2Al2ZrO13, a hexagonal perovskite-related oxide, as a new class of proton conductors exhibiting higher conductivities than 10–3 S cm–1 between 300 and 1200 °C. The protons as charge carriers are found to exist in the inherently oxygen-deficient h′ layer of Ba5Er2Al2ZrO13, which are supported by Rietveld analysis of neutron-diffraction data, bond-valence-based energy calculations, and thermogravimetric analysis. Our discovery of a new structure family of proton conductors with the inherently oxygen-deficient h′ layer offers a strategy in designing superior proton conductors based on hexagonal perovskite-related oxides. © 2020 American Chemical Society
- ItemHigh proton conductivity in β-Ba2ScAlO5 enabled by octahedral and intrinsically oxygen-deficient layers(John Wiley & Sons Inc., 2022-12-19) Murakami, T; Avdeev, M; Morikawa, R; Hester, JR; Yashima, MProton conductors are promising materials for clean energy, but most available materials exhibit sufficient conductivity only when chemically substituted to create oxygen vacancies, which often leads to difficulty in sample preparation and chemical instability. Recently, proton conductors based on hexagonal perovskite-related oxides have been attracting attention as they exhibit high proton conductivity even without the chemical substitutions. However, their conduction mechanism has been elusive so far. Herein, taking three types of oxides with different stacking patterns of oxygen-deficient layers (β-Ba2ScAlO5, α-Ba2Sc0.83Al1.17O5, and BaAl2O4) as examples, the roles of close-packed double-octahedral layers and oxygen-deficient layers in proton conduction are shown. It is found that “undoped” β-Ba2ScAlO5, which adopts a structure having alternating double-octahedral layer and double-tetrahedral layer with intrinsically oxygen-deficient hexagonal BaO (h') layer, shows high proton conductivity (≈10−3 S cm−1 above 300 °C), comparable to representative proton conductors. In contrast, the structurally related oxides α-Ba2Sc0.83Al1.17O5 and BaAl2O4 exhibit lower conductivity. Ab initio molecular dynamics simulations revealed that protons in β-Ba2ScAlO5 migrate through the double-octahedral layer, while the h′ layer plays the role of a “proton reservoir” that supplies proton carriers to the proton-conducting double-octahedral layers. The distinct roles of the two layers in proton conduction provide a strategy for developing high-performance proton conductors. © 2022 The Authors. Advanced Functional Materials published by Wiley-VCH GmbH.