Surface segregation-induced Cr depth-profiles were determined for Cr-doped single crystals at various temperatures (1373 to 1673K) and O partial pressures (102 to 105Pa). It was shown that the shape of the depth profiles depended upon both the annealing conditions and upon the subsequent cooling procedure. It was observed that during the slow cooling of specimens, from the high equilibrium segregation temperature to room temperature, there was a substantial change in the concentration profile. This involved Cr diffusion from the surface to the bulk, and resulted in its depletion. It was also shown that the rate of the de-segregation which resulted in a decrease in surface concentration was slower than the lattice transport of Cr. It was concluded that the de-segregation was rate-controlled by the decomposition of a spinel-type bi-dimensional surface structure which formed at high temperatures due to Cr segregation.

A.Bernasik, J.Nowotny, S.Scherrer, S.Weber: Journal of the American Ceramic Society, 1997, 80[2], 349-56