Computer simulation of defects in KTaO3.

Abstract

Using atomistic computer simulation methods we propose a general overview of the point defect structure of ${\mathrm{KTaO}}_{3}$. A set of short-range potential parameters was derived using an empirical fitting procedure. These parameters were then applied within the framework of the shell model. We employed a two-region strategy in combination with the Mott-Littleton technique for defect calculations. Intrinsic defects including Frenkel and Schottky-type disorder, polarons, and reduction/oxidation mechanisms are treated in the study as well as a great number of extrinsic defects. The way these ions are introduced into the crystal, their agglomeration into defect complexes and possible off-center displacements are investigated. It is found that in ${\mathrm{KTaO}}_{3}$, intrinsic disorder is of minor significance and small electron polarons possibly are stable. The calculations support the idea that reduction is significantly influenced by preexisting oxygen vacancies, which result from charge compensation 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-compensation, in some cases combined with the formation of oxygen vacancies.