Defect Chemistry of BaTiO₃ under Nonstoichiometric Ba/Ti Ratio

抄録

The equilibrium electrical conductivity of polycrystalline BaTiO₃ with nonstoichiometric Ba/Ti ratio was studied over the oxygen partial pressure of 10⁻¹⁵ to 1 atm, at temperatures higher than 1200°C. Conductivity results showed that more TiO₂ was incorporated into BaTiO₃ solid solution, resulting in the conductivity minimum shift. The oxygen vacancy content due to the extra TiO₂ was about three times as high as that of the stoichiometric composition, estimating from the relative position of the conductivity minimum. In contrast, the conductivity minimum of BaO excess samples was not shifted, which implies that the solubility of extra BaO in BaTiO₃ could not significantly exceed the background acceptor impurity (100 ppm). It is believed that the extrinsic oxygen vacancy due to the excess TiO₂ in BaTiO₃ could affect the microstructure development and dielectric degradation behavior.