Theoretical studies of diffusion processes down coincident tilt boundaries in NiO

Static minimization techniques have been used to study diffusion processes down coincident tilt boundaries in NiO. The activation energies calculated for cation vacancy hopping down grain boundaries were found to be significantly lower than the corresponding energy in bulk NiO. Indeed the ratios for the total activation energies of diffusion in the boundaries to the bulk value were found to range between 0·56 and 0·77 for the four boundaries considered. This compares favourably with the measured value of 0·7 for polycrystalline NiO. The total activation energy for anion interstitial diffusion was also found to be lower than the bulk value, but in this case the reduction was due to the large decrease in interstitial formation energy for the particular boundary considered.