Investigations on the local angular distortions and the spin-Hamiltonian parameters for Ni+ in sulfides

The local angular distortions and the spin-Hamiltonian parameters (the g factors and the hyperfine parameters) for Ni+ in ABS(2) (A=Cu, Ag; B=Al, Ga) ternary sulfides are theoretically investigated from the perturbation formulas of these parameters for 3d(9) ions in a tetragonally distorted tetrahedron. In view of the strong covalency of such systems, the ligand orbital and spin-orbit coupling contributions are taken into account using the cluster approach. The local impurity-ligand bond angles in the Ni+ centers are found to be about 1.4-4.5 degrees smaller than those of the host monovalent A sites in the pure crystals, due to size mismatching substitution. As a result, the ligand tetrahedra exhibit slight elongation in CuBS2:Ni+ and slight compression in AgGaS2:Ni+. The calculated spin-Hamiltonian parameters, optical transitions and the relative intensity ratios show reasonable agreement with the experimental data. (C) 2009 Elsevier B.V. All rights reserved.