An analytical correlation between O partial pressures and point defect concentrations was presented for perovskites. A clear distinction between 3 different influences was identified. These were the sintering conditions, an intermediate metastable state and a low-temperature metastable state. The analytical solution, for a metastable state which resulted from non-equilibrated metal vacancies, permitted a more accurate and self-consistent approach to be made to the deduction of the equilibrium constants from conductivity versus O2 partial-pressure data. One reason for the higher accuracy was that there was no need to divide the regime of existence into sub-regimes having differing approximations to the electroneutrality equation (Brouwer approximation). An excellent fit of the experimental conductivity data to a single function was obtained by using only 2 adjustable parameters over the entire conductivity versus O2 partial-pressure space. The relative importance of frozen-in metal vacancies and foreign acceptors was considered for BaTiO3.

Point Defect Concentrations in Barium Titanate Revisited. Y.Tsur, C.A.Randall: Journal of the American Ceramic Society, 2001 84[9], 2147-9