材料期刊网

The local structures and the spin Hamiltonian parameters (zero-field splittings D and E and the anisotropic g factors g(x), g(y) and g(z)) for the rhombic Ni(2+) centers in AgX (X = Cl, Br) are theoretically studied from the perturbation formulas of these parameters for a 3d(8) ion under rhombically distorted octahedra. In these formulas, the ligand p- and s-orbital and spin-orbit coupling contributions are included on the basis of the cluster approach. The rhombic centers are attributed to the impurity Ni(2+) associated with one nearest-neighbor silver vacancy V(Ag) along the [110] direction as charge compensation. Based on the calculations, Ni(2+) is found to suffer an off-center displacement 0.092 angstrom (or 0.335 angstrom) for AgCl (or AgBr) towards the V(Ag) along the [110] axis, while the ligands closest to the V(Ag) undergo a small shift 0.065 angstrom (or 0.006 angstrom) away from (or towards) the V(Ag). The theoretical spin Hamiltonian parameters based on the above defect structures show good agreement with the experimental data.