Electrical properties of A′Ca₂Nb₃O₁₀ (A′ = K, Rb, Cs) Layered Perovskite Ceramics

The electrical conductivity properties of Dion-Jacobson type layered perovskites A′Ca₂Nb₃O₁₀ (A′ = K, Rb, Cs) was investigated under different gas atmospheres. An increase in the electrical conductivity by about 2-5 orders in magnitude in both ammonia and hydrogen atmospheres is observed compared to air. Among the members of the series, the compound with the smallest size of the alkali ion, i.e. KCa ₂Nb₃O₁₀, exhibits the highest conductivity. In air and hydrogen, a single activation energy value in the range 0.25-0.80 eV is observed, while in ammonia a sharp increase in the electrical conductivity is found at about 500°C. The activation energy at low-temperatures (300-500°C) is attributed to ionic motion and at higher temperatures (500-700 °C) to both defect formation and ionic motion. The unusual electrical conductivity behavior in ammonia is explained on the basis of the model developed for alkali halides. EMF measurements reveal that the layered perovskites are ionic (proton) conductors. The electrical conductivity changes as a function of the ammonia gas concentration; accordingly, layered perovskites appear to be useful solid electrolytes in galvanic cells for practical applications, e.g. for gas sensors.