Theoretical investigations on the local structures and the g factors of three Ni3+ centers in LaSrAl1−xNixO4

The local structures and the EPR g factors of three Ni3+ centers (1)-(3) in LaSrAl1−xNixO4 (LSAN) are theoretically investigated from the perturbation formulas of the g factors for a 3d7 ion of low spin (S = 1/2) in tetragonally and orthorhombically distorted octahedra. In these formulas, the contributions to the g factors from the low symmetrical parts of the crystal-fields, characterized by the crystal-field parameters Ds, Dt, Dξ and Dη are taken into account. Based on the studies, it is found that the ligand octahedra are elongated along [0 0 1] axis by about 0.9, 0.7 and 1.0% for centers (1)-(3). The above distortions have a Jahn-Teller nature instead of ordinary lattice deformation, leading to the ligand octahedra less elongated than that (≈1.3%) in the host. Apart from the axial elongation, center (3) suffers additional orthorhombic distortion due to inequivalent variation by about ±0.3% of the planar bonding lengths along [1 0 0] and [0 1 0] axes, respectively. The calculated g factors show good agreement with the observed values.