Mixed oxide ion and proton conduction and p-type semiconduction in BaTi_0.98Ca_0.02O_2.98 ceramics

Ca-doped BaTiO₃, BaTi_0.98Ca_0.02O _2.98 is primarily an oxide ion conductor with activation energy 0.77(1) eV when annealed at 700 °C and measured in an atmosphere of dry N₂. On exposure of this sample to moisture, proton conduction dominates the conductivity at low temperatures with activation energy 0.42(1) eV but the sample reverts to mainly oxide ion conduction above ∼500 °C as water is lost from the sample. When samples are annealed at 700 °C and measured in an atmosphere of dry O₂, p-type semiconduction with activation energy 0.70(2) eV dominates. The nature of the conducting species was determined by a combination of conductivity measurements as a function of oxygen partial pressure and characteristic features in low frequency impedance data.