Chemical Diffusivity and Defect Chemistry of BaTiO_3−δ

Abstract

Chemical diffusion coefficient of BaTiO_3−δ was determined by a conductivity relaxation technique as afunction of oxygen partial pressure in the widest ever range of 10⁻¹⁵≤Po₂/atm≤1 including an n/p mixed regime, at elevated temperatures of 800≤T/°C≤1100. The chemical diffusivity varies convex-upwardly in the range of 10⁻⁵≤ /cm² s⁻¹ < 10⁻² at al1 temperatures and its maximum falls approximately at the oxygen partial pressure where n-to-p transition occurs or δ≈0. This behavior of is analyzed on the basis of C. Wagner's classic theory of chemical diffusion in association with the defect structure of BaTiO_3−δ. The measured total conductivity and chemical diffusivity combined leads, without using any assumptions, to the evaluation of the defect chemical parameters including carrier mobi1ities and defect equilibrium constants, and further to an insight into the nature of the inherent acceptors of “undoped’’ Ba-TiO_3−δ.