The migration of 57Co across (110) NiO surfaces was investigated by using the edge source method. The surface diffusion parameter, D, where  was the segregation factor, D was the surface diffusion coefficient, and  was the thickness of the high-diffusivity layer, was determined at temperatures ranging from 750 to 1200C. The Whipple solution was used to treat the experimental results. At higher temperatures, vapor transport appeared to be the predominant diffusion mechanism. At lower temperatures, ionic transport predominated. Ionic transport predominated, in the surface diffusion of 57Co, over the entire temperature range. This was explained in terms of a weak bond between Co-vapor species and the NiO surface. The results suggested that the surface diffusion of Co2+ ions at 750C was some 7 orders of magnitude faster than volume diffusion while, at 1200C, it was some 5 orders of magnitude faster than volume diffusion. The activation energies were 139 and 227kJ/mol, for surface and volume diffusion, respectively.

E.P.Macey, V.S.Stubican: Journal of the American Ceramic Society, 1993, 76[2], 557-9