Diffusion profiles were recorded  in situ  and were evaluated by using an optical technique. It was shown that theoretical calculations could reproduce the experimental data (figure 9), without using adjustable parameters, if account was taken of coupling of the diffusing species to internal redox changes in the dopants. Measurements on single crystals and on bicrystals, with and without crack formation, provided valuable information concerning the effect of free relaxed surfaces, freshly produced crack surfaces, and grain boundaries upon diffusion. In particular, the inward diffusion of O via crack surfaces was characterized by enhanced diffusion coefficients.

I.Denk, F.Noll, J.Maier: Journal of the American Ceramic Society, 1997, 80[2], 279-85