Papers by Keyword: Ni³⁺

Abstract: 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.

Abstract: The electron paramagnetic resonance (EPR) gyromagnetic factors for the Ni3+ center in MgO are theoretically investigated using the improved g formulas for a tetragonally elongated octahedral 3d7 complex suffering the dynamical Jahn-Teller effect. From the studies, the impurity Ni3+ center is found to undergo the relative elongation along the tetragonal axis by about 1%. The calculated g value shows good agreement with the observed result, and the improvement in the theoretical calculations is achieved in this work as compared with the previous treatments. The local structure of the impurity center is discussed.

Abstract: The axial displacements for Co2+ and Ni3+ in Al2O3 are theoretically investigated starting from the perturbation formulas of the EPR parameters for a 3d7 ion with high spin (S=3/2) and low spin (S=1/2) in trigonal symmetry, respectively. Based upon these studies, the Co2+ is found to shift towards the center of the oxygen octahedron by an amount
ZCo (≈ 0.03 Å) along the C3 axis, while the Ni3+ may suffer another axial displacement
ZNi (≈ −0.38 Å) away from the center of the octahedron. The calculated EPR parameters based upon the above axial displacements show good agreement with the observed values. The differences in the EPR parameters and the axial displacements for the two 3d7 ions are discussed.