The defect chemistry of sapphire (α-Al2O3)

The point defect chemistry in sapphire (alpha-Al2O3) has been investigated using traditional mass action calculations. These required a consistent set of defect formation and cluster binding energies, which were provided by atomistic simulation calculations. The defect reactions studied include those associated with intrinsic defects and the aliovalent impurities Mg2+ and Ti4+. Both perfect co-doping and doping that assumes an excess of Mg2+ or Ti4+ ions were considered. In all cases the intrinsic defect concentrations are dramatically affected by dopant ions, even at the p.p.m. level. This is a consequence of the high intrinsic defect formation energies. Thus, even in unintentionally doped sapphire, it is suggested that the point defect chemistry will be controlled by background trace impurity ions. (C) 1998 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All rights reserved.