Two-fold diffusion kinetics of oxygen re-equilibration in donor-doped BaTiO3

Oxygen (nonstoichiometry) re-equilibration kinetics was examined, via a conductivity relaxation method, on 1 m/o donor (La)doped BaTiO3 (nominal composition, Ba0.99La0.01Ti0.9975O3) against oxygen partial pressure in the range of -16 < log (P-O2/atm) <= 0 at 1200 degrees C. The kinetics has been found to be onefold with a single relaxation time or twofold with two different relaxation times depending on oxygen activity. It is attributed to the relative contributions depending on oxygen activity of fast relaxation of the oxygen sublattice and sluggish relaxation of the cation sublattices: their revelations are determined by the ratio of oxygen vacancy to cation vacancy (say, V-Ti) concentrations and their relaxation times. Their chemical diffusion coefficients have been extracted from the relaxation times as (D) over tilde (O)/cm(2)/s = 10(-4) similar to 10(-6) and D-Ti /cm(2)/s = 10(-15) similar to 10(-11) depending on oxygen activity, which are in good agreement with the reported values. Defect diffusivities are subsequently determined by using the thermodynamic factors of component O and Ti, which have been evaluated from the equilibrium conductivity isotherm, as D-Vo = (1.4(-0.9)(+2.7)) x 10(-5) cm(2)/s and D-VTi, = (1.4(-0.7)(+1.5)) X 10(-15) cm(2)/s.