It was recalled that oxidative cooling was a critical step during the processing of barrier-layer electro-ceramics that were based upon this material. It had been proposed that Ba vacancies formed at the grain boundaries in order to compensate donors, but no direct evidence for this mechanism existed. On the other hand, published data supported the compensation, of donors in the bulk, by Ba or Ti vacancies. Thus, the nature of the defects which formed at electrically active titanate grain boundaries during oxidation remained uncertain. The subject was investigated here by using scanning Auger electron spectroscopy, and observing changes in the surface composition of donor-doped BaTiO3 when cation vacancies were introduced during oxidation. Direct experimental support for the formation and in-diffusion of Ba vacancies during oxidative cooling was obtained in samples which contained 0.7%Nb. It was suggested that Ba vacancy compensation constituted a metastable defect equilibrium in BaTiO3. In the case of samples which contained 0.3%Nb, the results were inconclusive. This was attributed to a slower oxidation, that was limited by surface reaction kinetics.

A.Yamada, Y.M.Chiang: Journal of the American Ceramic Society, 1995, 78[4], 909-14