Atomistic simulations were used to evaluate the diffusion pathways and activation energies for cation and anion vacancy migration in {410}/[001] symmetrical tilt grain boundaries. These could be considered as being an array of dislocation pipes. The approach used was based upon molecular dynamics, and it was found that the diffusion paths were anisotropic; with diffusion down the dislocation pipes being favored over diffusion between the pipes. The lowest calculated activation energies for isolated vacancies were equal to 1.05eV for Mg and to 1.01eV for O at 0GPa. The bulk activation energies were equal to 1.94eV for Mg and to 2.12eV for O. The lower activation energies, coupled with increased defect concentrations at the interface, showed that the boundaries were regions of high diffusivity. However, the concentrations of vacancy pairs at the interface and the high binding energy of Mg-O pairs led to the prediction that a large fraction of the defects were bound. This in turn caused the activation energy for vacancy migration to approach that of the bulk. In this case, the higher boundary diffusivities were the result of high defect concentrations at the boundary.

D.J.Harris, G.W.Watson, S.C.Parker: Physical Review B, 1997, 56[18], 11477-84