Zhi Hong Zhang

Investigations on the local structure and spin Hamiltonian parameters for the orthorhombic Cu2+ center in Ca(OD)2

AbstactThe local structure and the spin Hamiltonian parameters (the g factors gi (i = x, y, z) and the hyperfine structure constants Ai) for Cu2+-doped Ca(OD)2 are theoretically investigated from the perturbation formulas of these parameters for a 3d9 ion in an orthorhombically elongated octahedron. From the studies, the planar Cu2+-OD− bonds are found to experience the relative variation ΔR (≈0.014 Å) along the X and Y axes, while those parallel to the Z axis may undergo the relative elongation ΔZ (≈0.25 Å) due to the Jahn-Teller effect. The theoretical spin Hamiltonian parameters based on the above local lattice distortions agree well with the experimental data. As compared with the previous treatments, the improvements of the theoretical spin Hamiltonian parameters are achieved in this work by adopting the uniform calculation formulas and the tetragonal field parameters based on the superposition model.

Theoretical Investigations of the Defect Structure for Ni3+ in ZnO

The defect structure for Ni3+ in ZnO crystal is theoretically investigated using the perturbation formulas of the spin Hamiltonian parameters for a 3d7 ion in trigonally distorted tetrahedra. In view of the significant covalency of the system due to the high valence state of Ni3+, the ligand orbital and spin-orbit coupling contributions are taken into account in a uniform way based on the cluster approach. The impurity Ni3+ is found not to occupy the ideal Zn2+ site in ZnO but to undergo the small axial displacement of about 0.044 Ǻ away from the oxygen triangle along the C3 axis. The theoretical spin Hamiltonian parameters based on the above impurity displacement show good agreement with the experimental data. The defect structure of this impurity center is compared with that for the similar Fe3+ in ZnO.

Theoretical Studies of the EPR Parameters for Rh+ in NaCl

The electron paramagnetic resonance (EPR) parameters g factor and the hyperfine structure constant A factor for the substitutional Rh+ in NaCl are theoretically studied from the perturbation formulas of these parameters for a 4d8 ion in cubic octahedra. In these formulas, the ligand orbital and spin-orbit coupling contributions which were normally omitted in the previous studies are taken into account using the cluster approach. The calculated g and A factors are in good agreement with the experimental data. The ligand contributions to the EPR parameters are somewhat important and should be considered in the analysis of the EPR spectra for a 4d8 ion in chlorides. The local structure of this center is also discussed.

Studies of the Spin Hamiltonian Parameters for NiX2 and CdX2:Ni2+ (X=Cl, Br)

The spin Hamiltonian parameters (zero-field splitting D and the g factors) for NiX2 and CdX2:Ni2+ (X=Cl, Br) are quantitatively investigated from the perturbation formulas of these parameters for a 3d8 ion in trigonally distorted octahedra based on the cluster approach. In the calculations, the trigonal field parameters uf06e and uf06euf020′ are determined from the superposition model and the local structures of Ni2+ in the halides. The theoretical g factors show reasonable agreement with the observed values, and the experimental D for CdX2:Ni2+ are also interpreted by considering suitable lattice distortions (angular decreases) in the impurity-ligand bond angles related to the C3 axis due to the size mismatching substitution. The contributions from the ligand orbital and spin-orbit coupling interactions are important and should be taken into account.

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 [100] (or C4) axis. The calculated EPR parameters based on the above defect structures show reasonable agreement with the experimental data.