Tracer diffusivities were deduced from measurements of the rate of weight-gain, of monocrystalline samples, that resulted from the exchange of 18O and 16O between solid and water in the gas phase. By combining the tracer diffusivities with self-diffusion coefficients (deduced from conductivity measurements), the correlation factor for O diffusion was estimated to be 0.65, when the anion vacancies were assumed to be doubly ionized. By exploiting the proportionality of the self-diffusivity and the vacancy concentration, it was possible to determine the anion vacancy diffusion coefficient. It was found that the presence of H in the gas increased the O diffusivity by about 10%. The low O potential of H-containing gas was attributed to an increase in the anion vacancy concentration. Depending upon the type of sample, the pre-exponential factor for O diffusion took values of 5.4 x 10-7, 7.3 x 10-7, 3.7 x 10-7 or 1.6 x 10-4cm2/s, with corresponding activation energies of 13.3, 14.0, 13.4 or 21.1kcal/mol. The vacancy diffusivity could be described by:

D (cm2/s) = 0.0047 exp[-15.4(kcal/mol)/RT]

K.Park, D.R.Olander: Journal of the Electrochemical Society, 1991, 138[4], 1154-9