Density-functional and shell-model calculations of the energetics of basal-plane stacking faults in sapphire

First-principles density-functional calculations have been performed for ba sal-plane stacking faults in sapphire (alpha -Al2O3). The present results c onfirm predictions of empirical atomistic studies where these faults are fo und to have high energies. Examination of the cation-layer stacking sequenc es along [0001] shows that important changes in the Al-Al coordination occu r; with respect to the bulk, several cations have additional or no cation n earest neighbours in adjacent basal cation layers. The obtained generalized stacking-fault energies for displacement paths along the close-packed [10 (1) over bar0] directions of the oxygen sublattice are discussed in connect ion with existing theories of basal slip and twinning.