Transition-metal ion impurities in KTaO3 -: art. no. 012102

A systematic study of transition-metal impurity centers in pervoskites is undertaken by considering isolated Co2+, Fe3+, and Cu2+ point defects, in KTaO3. Within the generalized gradient approximation (GGA), the defect center magnetic moments agree with experiments, except for A-site Fe3+ complexes which exhibit 3mu(B) and 5mu(B) structures competitive in energies. It is argued that the anomaly is an artifact of GGA, which underestimates Fe3+ 3d electron correlations. Large (similar to1 Angstrom) off-center displacements of K-substituting impurities obtain due to metal-oxygen covalent bonding. These A-site dipoles exhibit relaxation dynamics barriers which agree well with experiments, The Fe3+-O-1(2-) complex is considered in some detail; it exhibits Fe-O bonds considerably shorter than shell-model predictions.