Theoretical investigations on the local structures and the g factors of three Ni~(3+) centers in LaSrAl_(1-x)Ni_xO_4

摘要

The local structures and the EPR g factors of three Ni~(3+) centers (l)-(3) in LaSrAl_(1-x)Ni_xO_4 (LSAN) are theoretically investigated from the perturbation formulas of the g factors for a 3d~7 ion of low spin (S= 1/2) in tetragonally and orthorhombically distorted octahedra. In these formulas, the romnbations to the g factors from the low symmetrical parts of the crystal-fields, characterized by the crystal-field parameters D_s, D_t, D_(zeta) and D_(eta) are taken into account. Based on the studies, it is found that the ligand octahedra are elongated along [0 01] axis by about 0.9, 0.7 and 1.0 percent 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 (approx = 1.3 percent) in the host. Apart from the axial elongation, center (3) suffers additional orthorhombic distortion due to inequivalent variation by about + - 0.3 percent of the planar bonding lengths along [100] and [010] axes, respectively. The calculated g factors show good agreement with :bo observed values.