AA′₂M₃O₁₀ (A = K, Rb, Cs; A′ = Ca; M = Nb) layered perovskites: Low-temperature proton conductors in hydrogen atmospheres

Electrical conductivity of the Dion-Jacobson (D-J) type layered perovskite oxides, AA′₂M₃O₁₀ (A = K, Rb, Cs: A′=Ca; M=Nb, Ta), is determined by AC impedance analysis in hydrogen atmospheres and in air. The electrical conductivity behavior of the layered perovskite oxides in hydrogen is different from that in air. Among the layered perovskites, KCa₂Nb₃O₁₀ exhibits the highest electrical conductivity, σ, of 3.2 × 10^-4 S cm^-1 at 45 °C with an activation energy, E_a of 0.25 eV in a hydrogen atmosphere. Open circuit voltage measurements at room temperature with hydrogen-oxygen gas concentration cells reveal that the mobile charge carriers are most likely protonic in origin. The electrical (proton) conductivity is comparable to that of fast lithium ionic conductors based on the perovskite structure such as (Li,La)TiO₃ at the same temperature.