Estimation of ionic and hole conductivity in bismuth titanate polycrystals at high temperatures

Oxide ionic and hole conduction of bismuth titanate (Bi4Ti3O12) polycrystals were investigated by measuring oxygen partial pressure dependence of electrical conductivity. Bismuth titanate showed mixed conduction of oxide ion and electron hole in the temperature range of 600 to 750 °C. The ionic conductivity was larger than hole conductivity above 600 °C, and much larger above Curie temperature (675 °C). The jump of ionic and hole conductivities was observed around the Curie temperature. Detailed impedance analysis taking inhomogeneity in polycrystalline specimens into account were also performed on the basis of a simple equivalent circuit. Ionic and hole conductivities estimated by impedance calculation showed an excellent agreement with those estimated from oxygen partial pressure dependence of the conductivities.