Crystal structure and electrical conductivity of BaR₂ZnO₅ (R = Sm, Gd, Dy, Ho, and Er)—a new structure family of oxide-ion conductors

Abstract

Metal oxides containing the divalent zinc cation (Zn²⁺, d¹⁰ electronic configuration) as an essential element are promising candidates for oxide-ion conductors, because there are several good oxide-ion conductors containing other d¹⁰ cations, such as Ga³⁺ and Ge⁴⁺. In the present study, we have found a new structure family of oxide-ion conductors, BaY₂CuO₅-type (BaCuY₂O₅-type) BaR₂ZnO₅ compounds (R = rare earths). BaR₂ZnO₅ compounds with a BaY₂CuO₅-type structure were found to be good candidates for oxide-ion conductors by the bond-valence method. BaR₂ZnO₅ compounds (R = Sm, Gd, Dy, Er, and Ho) were synthesized by solid-state reactions, and their electrical conductivities and crystal structures were investigated. Rietveld analyses of BaR₂ZnO₅ (R = Sm, Gd, Dy, Er, and Ho) using synchrotron X-ray powder diffraction data gave good fitting for the BaY₂CuO₅-type structure. BaHo₂ZnO₅ had the highest total electrical conductivity in air among BaR₂ZnO₅ compounds (R = Sm, Gd, Dy, Er, Ho). Oxide-ion conduction was confirmed for BaHo₂ZnO₅ by electrical conductivity measurements conducted under various oxygen partial pressures. Neutron powder diffraction data of BaHo₂ZnO₅ were analyzed by the Rietveld method, and the oxide-ion conduction paths were investigated by the bond-valence method.