Theoretical studies of the EPR parameters and the local structure of the tetragonal Fe+ center in KTaO3

The EPR parameters (zero-field splitting D and g factors g parallel and g perpendicularto) and the local structure for the tetragonal Fe+ center in KTaO3 are theoretically studied by using the perturbation formulas of the EPR parameters for a 3d7 ion in tetragonally distorted dodecahedra. Based on these studies, we find that the impurity Fe+ may not locate on the regular dodecahedral K+ site but suffer a large off-center displacement ΔZ (∼ 0.43 Aa) along one of the <100> (or C4) axes, which is responsible for the large tetragonal distortion of the impurity center. The displacement ΔZ obtained in this work is comparable with that (∼0.46 Aa) of a similar monovalent Li+ on K+ site of KTaO3 obtained from the nuclear quadrupole shift and can be regarded as reasonable. The calculated g factors, particularly the anisotropy Δg (=g perpendicular to -g parallel) based on the above displacement, agree with the observed values. (orig.)