THE DEFECT CHEMISTRY OF SAPPHIRE (ALPHA-AL2O3)

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