Crystal structure and electrical conductivity of Ba<i>R</i><sub>2</sub>ZnO<sub>5</sub> (<i>R</i> = 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.