VACANCY MIGRATION AT THE (410) [001] SYMMETRICAL TILT GRAIN-BOUNDARY OF MGO - AN ATOMISTIC SIMULATION STUDY/

We present the results of atomistic simulations to evaluate diffusion pathways and hence activation energies for cation and anion vacancy mi gration in the MgO {410}/[001] symmetric lilt grain boundary, which ca n be considered as a series of dislocation pipes. The approach employe d in this study is based on molecular dynamics and we found that tile diffusion routes were anisotropic with diffusion down the dislocation pipes favored over diffusion between the pipes. The lowest calculated activation energies for isolated vacancies were 1.05 eV for magnesium and 1.01 eV for oxygen at 0 GPa (cf. bulk activation energies of 1.94 eV for magnesium and 2.12 eV for oxygen). The lower activation energie s coupled with the enhanced defect concentrations at the interface Sho ws that boundaries are regions of high diffusivity. However, the conce ntration of vacancy pairs at the interface and the high binding energy of a magnesium-oxygen pair leads to the prediction that a large compo nent of the defects is bound, which in turn causes the activation ener gy for vacancy migration to approach that of the bulk. In this case th e higher boundary diffusivities are the result of high defect concentr ations at the boundary. [S0163-1829(97)04442-1].