Oxide Ion and Proton Conductivity in a Family of Highly Oxygen-Deficient Perovskite Derivatives

Functional oxides showing high ionic conductivity have many important technological applications. We report oxide ion and proton conductivity in a family of perovskite-related compounds of the general formula A(3)OhTd(2)O(7.5), where Oh is an octahedrally coordinated metal ion and Td is a tetrahedrally coordinated metal ion. The high tetrahedral content in these ABO(2.5) compositions relative to that in the perovskite ABO(3) or brownmillerite A(2)B(2)O(5) structures leads to tetrahedra with only three of their four vertices connected in the polyhedral framework, imparting a potential low-energy mechanism for O2- migration. The low- and high-temperature average and local structures of Ba3YGa2O7 (P2/c, a = 7.94820(5) angstrom, b = 5.96986(4) angstrom, c = 18.4641(1) angstrom, and beta = 91.2927(5) degrees at 22 degrees C) were determined by Rietveld and neutron pair distribution function (PDF) analysis, and a phase transition to a high-temperature P112(1)/a structure (a = 12.0602(1) A, b = 9.8282(2) A, c = 8.04982(6) A, and y = 107.844(3)degrees at 1000 degrees C involving the migration of O2- ions was identified. Ionic conductivities of Ba3YGa2O7.5 and compositions substituted to introduce additional oxide vacancies and interstitials are reported. Most phases show proton conductivity at lower temperatures and oxide ion conductivity at high temperatures, with Ba3YGa2O7.5 retaining proton conductivity at high temperatures. Ba2.9La0.1YGa2O7.55 and Ba3YGa1.9Ti0.1O7.55 appear to be dominant oxide ion conductors, with conductivities an order of magnitude higher than that of the parent compound.

Automated summary

Functional oxides with high ionic conductivity have important technological applications. The addition of oxide vacancies and interstitials can enhance ionic conductivity in perovskite-related compounds.