Chemical diffusion in complex oxides with an emphasis on BaTiO3

Abstract

Chemical diffusion has long been studied mostly on binary oxides, but practical interest in it is increasing with more complex oxides these days, e.g., perovskite oxides that are finding a variety of electroceramic and electrochemical applications. In this paper, we compile the chemical diffusivity data of oxygen as measured on a prototype perovskite BaTiO₃ and review the connotation of their variation with oxygen activity in the light of the chemical or ambipolar diffusion theory. The chemical diffusivity of BaTiO₃ is compared with those of other perovskite oxides of mostly electrochemical concern and of typical binary transition metal oxides. The chemical diffusivity is further compared with those of the compounds such as Ag₂S, Ag₂Te, YSZ and Fe₃O₄, that have dissimilar crystal structures, but with a similar defect structure to BaTiO₃, in order to get a further insight into the inner workings of chemical diffusivity particularly in the stoichiometric regime of complex oxides. Finally, possible complication with nonstoichiometry re-equilibration kinetics due to cation mobility is pointed out with reference to what has been observed from LiNbO₃ under an oxygen activity gradient.