DEFECT STRUCTURE, ELECTRICAL-PROPERTIES AND TRANSPORT IN BARIUM-TITANATE .6. GENERAL DEFECT MODEL

Electrical conductivity data are analysed in terms of defect equilibria for undoped BaTiO3 within a wide range of temperatures and oxygen partial pressures. Based on the Hall effect data reported by Seuter the equilibrium constants of the formation of (1) oxygen vacancies (K1), (2) Schottky disorder and (3) intrinsic disorder (K(i)) were determined. The defect diagram of BaTiO3 thus derived involves four regimes of different charge neutrality. The effect of doping with aliovalent ions on the concentration of intrinsic defects was also determined. It was shown that the validity of the extrinsic disorder is limited to the n-type regime. It has been argued that any model constructed in the p-type regime cannot ignore the formation of cation vacancies. A defect model based on a general charge neutrality was derived. The model is valid within a wide range of compositions involving both n- and p-type regimes, except extremely reducing conditions. The resulting defect diagrams indicate that Schottky-type defect structure predominates in undoped BaTiO3 in the p-type regime.