Chemical diffusivity of BaTiO3-δ:: Defect chemical analysis

The chemical diffusivity of undoped BaTiO3-delta which was measured in Song and Yoo [Solid St. Ionics 120, 141 (1999)] is analyzed on the basis of the defect structure proposed and Wagner's classic theory of chemical diffusion. It is confirmed that a maximum of isothermal chemical diffusivity around the stoichiometric composition (delta = 0) is of thermodynamic origin. The combination of the isotherms of both electrical conductivity and chemical diffusivity enables one to evaluate, without recourse to any assumption at all, the concentration product of electrons and holes, K-i(= np), as well as the mobilities of electrons and holes, mu(n), and mu(p), separately.