Nature of Cation Vacancies Formed to Compensate Donors during Oxidation of Barium Titanate

Abstract

Oxidative cooling is a critical step in the processing of barrier layer electroceramics based on BaTiO3. While it has been proposed that barium vacancies are formed at the grain boundaries to compensate donors,1, 2 no direct evidence for this mechanism exists. On the other hand, literature data can be found to support the compensation of donors in the bulk by either barium or titanium vacancies. As a result the defect(s) formed at electrically active titanate grain boundaries during oxidation has remained uncertain. We explore this phenomenon by observing changes in the surface composition of donor‐doped BaTiO3 when cation vacancies are introduced during oxidation, using SAES (scanning Auger electron spectroscopy). Direct experimental support for the formation and in‐diffusion of barium vacancies during oxidative cooling is obtained in a composition containing 0.7% Nb. It is suggested that barium vacancy compensation constitutes a metastable defect equilibrium in BaTiO3. In a sample of lower concentration (0.3% Nb), results are inconclusive, perhaps because of slower oxidation limited by surface reaction kinetics.