Shell-model calculation of some point-defect properties inα−Al2O3

A polarizable point-ion shell model has been developed for $\alpha -{\mathrm{Al}}_2{\mathrm{O}}_3$. The material is treated as perfectly ionic, the repulsive interactions were calculated from free-ion wave functions, and the single empirical parameter of the model was obtained from an analysis of dielectric data. The model yields a good account of the cohesive properties of the perfect crystal. Calculations of the formation energy of vacancies and interstitials predict that Schottky defects are energetically more favorable than Frenkel pairs. Preliminary calculations of defect motion energies suggest that ${\mathrm{O}}^{2-}$ vacancies are the most mobile defect. Existing data on diffusion and radiation-damage annealing are reviewed in light of the calculations.