COMPUTER-SIMULATION OF DEFECTS IN KTAO3

Using atomistic computer simulation methods we propose a general overv iew of the point defect structure of KTaO3. A set of short-range poten tial parameters was derived using an empirical fitting procedure. Thes e parameters were then applied within the framework of the shell model . We employed a two-region strategy in combination with the Mott-Littl eton technique for defect calculations. Intrinsic defects including Fr enkel and Schottky-type disorder, polarons, and reduction/oxidation me chanisms are treated in the study as well as a great number of extrins ic defects. The way these ions are introduced into the crystal, their agglomeration into defect complexes and possible off-center displaceme nts are investigated. It is found that in KTaO3, intrinsic disorder is of minor significance and small electron polarons possibly are stable . The calculations support the idea that reduction is significantly in fluenced by preexisting oxygen vacancies, which result from charge com pensation of accidental acceptor impurities in the material. Extrinsic monovalent ions substitute on the potassium site for which no charge compensation is necessary. Ions of other valencies are incorporated on both cation lattice sites which then gives rise to a charge self-comp ensation, in some cases combined with the formation of oxygen vacancie s.