The diffusion of doubly-charged Ni vacancies in a Σ = 5 (310)[001] tilt grain boundary was studied by using molecular dynamics techniques. The simulations were carried out for a constant number of particles, volume, and temperature, and interatomic interactions were described by invoking a rigid ion potential. An analysis of the atomic trajectories showed that the diffusion of vacancies occurred via jumps between first-neighbor sites. The migration path involved only a restricted number of sites in the grain boundary, and the residence time of the vacancy on the most frequently visited sites was computed. There was no direct relationship between the frequencies of visits, and the vacancy formation energies that were calculated for these sites. The vacancy jump frequencies were calculated and the diffusion coefficient of this defect at high temperatures was deduced. Vacancy diffusion was slightly faster along the direction parallel to the grain boundary tilt axis than in the perpendicular direction. The degree of anisotropy was consistent with experimental data on other oxides. Bulk diffusion of the Ni vacancy was investigated by means of simulations of a perfect crystal. A qualitative analysis of the atomic trajectories showed that Ni diffusion was enhanced at the boundary.

T.Karakasidis, M.Meyer: Physical Review B, 1997, 55[20], 13853-64