Investigations on the impurity displacements and the g factors of the two tetragonal Ni3+ centres in SrTiO3

Abstract

The impurity displacements and the g factors g∥ and g⊥ of the two tetragonal Ni3+ centres (I and II) in SrTiO3 are theoretically investigated by using the perturbation formulae of the g factors for a 3d7 ion with low spin (S=1/2) in tetragonally distorted octahedra. In these formulae, the contributions to the g factors from the tetragonal distortion, the ligand spin–orbit coupling coefficient, and the ligand orbitals, which were usually neglected in previous studies (Muller K A et al 1969 Phys. Rev. B 186 361; Lacroix R et al 1964 Helv. Phys. Acta 37 627), are taken into account based on the cluster approach. Centre I (or II) was ascribed to the substitutional Ni3+ at the Ti4+ site, associated with the nearest neighbour oxygen vacancy VO (or the near neutral VO−(−2e)) along the C4 axis as a compensator. The impurity Ni3+ is found to shift away from (or towards) the compensator by about 0.033 nm (or 0.010 nm) along the C4 axis, respectively. As a result, the ligand octahedron around the impurity is elongated (compressed) in centre I (II), corresponding to the negative (positive) anisotropy Δg (=g∥−g⊥). The theoretical g factors based on the above impurity displacements show good agreement with the observed values.