The diffusion of 139Ce in polycrystalline NiO was studied at 600 to 1100C, under O at a pressure of 1atm. The solubility of Ce in the NiO bulk was negligible, but Ce was soluble at NiO grain boundaries and dislocations. Consequently, the Ce tracer diffused only along these pathways, and the resultant profiles were analyzed in order to give grain boundary,

D (cm2/s) = 6.3 x 10-4 exp[-2.0(eV)/kT]

 and dislocation diffusion coefficients. When combined with previous measurements of Ni and Co diffusion, it was found that grain-boundary coefficients decreased in the order: Co, Ni, Cr, Ce; as was also found for lattice diffusion (except for Ce, with its negligible bulk solubility).

A.Atkinson, R.I.Taylor: Journal of Physics and Chemistry of Solids, 1986, 47[3], 315-23