Octahedral 3d ~ 9-ion Spin Hamiltonian Parameters Of Theoretical Research

Based on the crystal field theory, perturbation formulas of the spin Hamiltonian parameters g-factors (fourth-order) and the hyperfine structure constants (third-order) of 3d9 ions under tetragonal symmetry (elongated octahedral) are established for the cases of small spin-orbit coupling coefficients (or weak covalency) and large spin-orbit coupling coefficients (or strong covalency) of the ligands. As for the ligands of larger ligand spin-orbit coupling coefficient (or strong covalency) such as Cl? and Br?, the contributions from the spin-orbit coupling and the p- and s- orbitals of the ligands are taken into account based on the cluster approach. Most importantly, the contributions from the charge transfer mechanism (related to charge transfer energy levels) which were usually neglected in previous treatments are included here, besides those from the crystal-field mechanism (related to crystal-field energy levels) considered in the previous works. Meanwhile, some model parameters in the formulas are connected with the local defect strcture and the optical spectra of the studied systems. Thus, the theoretical model and formulas seem superior to the more complicated ones in the previous treatments with many (eleven) adjustable parameters.The above perturbation formulas are then applied to LaSrAlO4:Cu2+ and K2PdX4 (X=Cl,Br):Cu2+, respectively, and the calculated values show good agreement with the experimental data. By analyzing the observed EPR spectra, the defect structure for Cu2+ in SrLaAlO4 can be described as one delocalized hole at the four planar oxygen ligands due to charge compensation, making the four planar Cu-O bonds shift outward by about 0.06 ?. As for Cu2+in K2PdX4 (X=Cl,Br) crystal, the theoretical results reveal that the charge transition contributions are obvious and unnegligible. In addition, the contributions from the charge transfer mechanism for X=Br? are much larger than those for X= Cl? due to the larger spin-orbit coupling coefficient and covalency of the former.