A new structure family of oxide-ion conductors Ca_0.8Y_2.4Sn_0.8O₆ discovered by a combined technique of the bond-valence method and experiments

Mg₃TeO₆-type Ca_0.8Y_2.4Sn_0.8O₆ has been found as a new structure family of oxide-ion conductors. From bond-valence-based energy (BVE) calculations for 147 compositions, which contain tin (Sn) as an essential element, Mg₃TeO₆-type Ca_0.8Y_2.4Sn_0.8O₆ was found to have a low energy barrier for oxide-ion migration. Ca_0.8Y_2.4Sn_0.8O₆ was synthesized by the solid-state reaction, and its electrical conductivity and crystal structure were investigated. The total electrical conductivity at various partial oxygen pressures and band gap estimated from the UV-vis spectrum suggested that Ca_0.8Y_2.4Sn_0.8O₆ is a pure oxide-ion conductor. The activation energy for the oxide-ion conductivity of Ca_0.8Y_2.4Sn_0.8O₆ was 1.39(4) eV. Synchrotron X-ray powder diffraction data of Ca_0.8Y_2.4Sn_0.8O₆ at 300 and 1273 K were successfully analyzed with the Mg₃TeO₆-type structure. The BVE calculation using the refined crystal structure of Ca_0.8Y_2.4Sn_0.8O₆ at 1273 K strongly suggested three dimensional oxide-ion diffusion.