Chemical diffusivity of BaTiO3−δ: I. Experimental determination

The chemical diffusivity of ‘undoped' polycrystalline BaTiO_3?δ was determined via a conductivity relaxation technique, at elevated temperatures (800≤T/°C≤1100) as a function of the ambient oxygen partial pressure in the range of 10^?16≤P_O2/atm≤1 including an n- to p-type transition regime. Mathematical formulation was developed to convert conductivity relaxation to the corresponding nonstoichiometry (δ) relaxation in the transition regime. It has been found that the chemical diffusivity appears to exhibit a maximum at the n-to-p transition point where the electronic minimum conductivity falls, and that surface reaction becomes more rate-determining than diffusion as the transition point is approached from both n-type and p-type branches. Experimental details are given and the results are exhaustively compared with those reported up to date on the ‘undoped' BaTiO₃.