The chemical diffusion coefficient was determined by using a conductivity relaxation technique, as a function of O partial pressures ranging from 10-15 to 1atm, at 1073 to 1373K. It was found that the chemical diffusivity plot was convex-upwards between 10-5 and 10-2cm2/s, at all temperatures. The maximum was located roughly at the O partial pressure where an n-to-p transition occurred. This behavior was explained by the ambipolar diffusion of mobile oxide ions and electrons.

Defect Structure and Chemical Diffusion in BaTiO3. H.I.Yoo, C.R.Song: Solid State Ionics, 2000, 135[1-4], 619-23