EPR g factors and tetragonal distortion for the isoelectronic Ni+ and Cu2+ centers in the CuGaSe2 crystal

The EPR g factors, g|| and g⊥, for the isoelectronic 3d9 ions Ni+ and Cu2+ at the tetragonal Cu+ site of the CuGaSe2 crystal are calculated from the high-order perturbation formulas based on a two-spin–orbit-parameter model. In the model, both the contributions to g factors from the spin–orbit parameter of central 3d9 ion and that of ligand ion are contained. The calculated results appear to be consistent with the experimental values. The tetragonal distortions (characterized by θ−θ0, where θ is the angle between the metal–ligand bond and C4 axis, and θ0≈54.74° is the same angle in cubic symmetry) of Ni+ and Cu2+ centers, which are different from the corresponding angle in the host CuGaSe2 crystal and from impurity to impurity, are obtained from the calculations. The difference of the sign of g||−g⊥ between the isoelectronic Ni+ and Cu2+ centers is found to be due to the different tetragonal distortions of both centers in the CuGaSe2 crystal.

Research Highlights
► The EPR g factors g|| and g⊥ for the isoelectronic 3d9 ions Ni+ and Cu2+ at the tetragonal Cu+ site of the CuGaSe2 crystal are calculated from high-order perturbation formulas based on a two-spin-orbit-parameter model.
► The tetragonal distortions of Ni+ and Cu2+ centers in the host CuGaSe2 crystal are obtained from the theoretical analysis.
► The difference of the sign of g||−g⊥ between the isoelectronic Ni+ and Cu2+ centers is found to be due to the different tetragonal distortions of both centers in the CuGaSe2 crystal.