Investigations of the Defect Structures and EPR Parameters for the Tetragonal and Cubic Ni2+ Centers in AgX (X=Cl, Br)
The defect structures and the electron paramagnetic resonance (EPR) parameters zero-field splitting and the g factors for the tetragonal and cubic Ni2+ centers in AgX (X=Cl, Br) are theoretically studied from the perturbation formulas of these parameters for a 3d8 ion in tetragonal and cubic octahedra. In these formulas, the ligand s-orbital contributions, which were usually neglected in the previous studies, are taken into account based on the cluster approach. The ligand X− intervening in the Ni2+ and the next nearest neighbour Ag+ vacancy VAg is suggested to suffer a small inward displacement (≈ 0.11 or 0.15Å for AgCl or AgBr, respectively) towards Ni2+ along the  (or C4) axis. The calculated EPR parameters based on the above defect structures show reasonable agreement with the experimental data.
D. J. Fisher
Z. H. Zhang et al., "Investigations of the Defect Structures and EPR Parameters for the Tetragonal and Cubic Ni2+ Centers in AgX (X=Cl, Br)", Defect and Diffusion Forum, Vol. 272, pp. 117-122, 2007