Abstract
The PTC-type BaTiO 3 ceramics of similar microstructure are obtained by careful control of a sintering scheme. The defect chemistry of them is modified by varying the cooling rate and annealing conditons. In addition to applying Heywang and Jonker models for explaining the resistivity anomaly of these samples, the outward diffusion of oxygen vacancies (V O ), which left excess barium vacancies (V Ba ) behind, is proposed to be the formation mechanism of surface states. The formation of defect complex consisting of a V O .. - Ba ″ pair is assumed to be the cause of small diffusivity of V O in these materials. The phenomena, in which the slower cooling rate raises the resistivity of samples, is ascribed to the higher concentration of excess barium vacancies (V Ba ) contained in these samples. However, the maximum potential barrier height (φ max ) of the samples is the same, irrespective of the amount of surface state concentration (N s ) and is estimated to be φ max = 0.66eV, from the In (ρ{variant} max )-1/T max plot. © 1990 Chapman and Hall Ltd.