Theoretical studies on the off-center displacement of Ni 3+ in SrO by analyzing its anisotropic g factors

Abstract

The off-center displacement of Ni 3+ ion in SrO crystal is investigated by analyzing its anisotropic g factors g // and g ⊥ by using the perturbation formulas of the g factors for a 3d 7 ion in axial (tetragonal or trigonal) symmetry. In these formulas, the contributions to the g factors from the mixture of different energy states, low symmetry distortion and covalency effect are included and the parameters related to these effects can be obtained from the optical spectral and local structural parameters of the studied system. Based on the studies, it is found that the Ni 3+ impurity may take an off-center displacement by about 0.23 Å along the [1 1 1] direction and result in a trigonally distorted [NiO 6] 9− cluster. Interestingly, the observed Ni 3+ center has the unusual 4T 1 ground orbital triplet due to the weak crystal field of the host SrO, which is different from the usual 2E ground orbital doublet for Ni 3+ under strong octahedral fields. The reasonableness of the results is discussed.