The mechanism of near-surface isotope diffusion was investigated by using the edge source method. The activation energy for the localized surface diffusion of 57Co on the (110) NiO surface was 139kJ/mol, as compared with those for grain boundary and volume diffusion (180 and 227kJ/mol, respectively). The surface diffusion of Co2+ ions at 800C appeared to be between 1 and 2 orders of magnitude faster than grain boundary diffusion, and 6 orders or magnitude faster than volume diffusion. The effect of point

defects upon the near-surface diffusion of 57Co was very similar to the effect upon volume diffusion. It was concluded that similar mechanisms were involved in both near-surface and lattice diffusion.

V.S.Stubican: Philosophical Magazine A, 1993, 68[4], 809-18

Table 153

Grain-Boundary Diffusion of 57Co in NiO