Investigations on the Defect Structures for the Tetragonal V²⁺ Centers in LiF and AgCl

The defect structures for the tetragonal V2+ centers in LiF and AgCl are theoretically studied from the perturbation formulas of the Electron Paramagnetic Resonance (EPR) parameters for a 3d3 ion in tetragonal symmetry based on the cluster approach. The structure model proposed in this work suggests that the ligand intervening in the impurity V2+ and the next-nearest-neighbouring cation vacancy (VC) in the C4 axis is expected to suffer an off-center displacement △Z towards the former due to electrostatic repulsion. The theoretical EPR parameters based on the above defect structures show a good agreement with the observed values.