Defect structure and oxygen diffusion in undoped and La-doped polycrystalline barium titanate

Oxygen diffusion coefficients in undoped and La-doped polycrystalline barium titanate were measured at an ambient oxygen pressure of about 40 Torr over the temperature range 770–1430 °C by a solid–gas exchange technique of O18. The undoped material was characterized only by an extrinsic region with a high diffusivity, whereas two types of La-doped materials displayed an intrinsic region with E?100 kcal/mol in addition to a common extrinsic region of a very low level of diffusivity. New ideas concerning defect equilibria for the doped materials are proposed for the extrinsic and intrinsic region. In addition, the origin of semiconducting behavior characteristic of the doped specimens is interpreted on a basis of new idea.