Theoretical Investigations Of The Local Structure And EPR Parameters For The 3d~n Ions

Electron paramagnetic resonance (EPR) spectrum is an significant tool to investigate the microcosmic local structure, magnetic and optical properties of crystals and complexes doped with transition-metal and rare-earth ions. EPR experimental results are usually described by the spin Hamiltonian parameters(Zero-field splittings,g factors and hyperfine structure constants,et. al).There are lots of EPR experiments for the 3d3,5,9 cluster. However, most of the theoretical explanations related to the above experimental results are unsatisfactory because the contribution arising from the charge transfer(CT), the ligand orbitals and spin-orbital coupling are not included in the traditional crystal model. The various adjustable parameters (eg. the crystal field parameters and so on) introduced in the description of the low-symmetry and the defect local structures are not quantitativly connect with the discussion for the Spin Hamiltonian Parameters (SHP). Hence the local structure information of the impurity centers are difficult to obtain.In order to conquer the above disadvantages, the high order perturbation formulas established from the improved cluster model are utilized in the systematic theoretical treatments for the SHP of 3d3,5,9 and 4f3 ions cluster. The local information of the defects are acquired and the following EPR phenomenon are reasonably explained:(i) In the rhombic substitutional Fe3+, Cr3+ and Mn4+ in rutile (TiO2) single crystal, the impurity centres are found to undergo the local axial distortions △Z and the planar bond angle variations △φp for Fe3+, Cr3+ and Mn4+, respectively. The signs for ZFSs D and E are analyzed in the light of those for △Z and rhombic distortion angle δφ<p (=φ’-π/4) related to an ideal octahedron. The magnitudes of △Z and △φ are conveniently illustrated by the axial and perpendicular ZFS relative variations △F and △G for the deviations of D and E based on the local distortion parameters from those (DH and EH) based on the host structural data of Ti4+ site, (ⅱ) The three Cr(CN)63-centres in NaCl are studied at three temperatures, the signs and magnitudes of the ZFSs D and E are in accordance with those of average bond length discrepancy △R (=(1/6)∑δRi, i=1-6) and rhombic distortion parameter H(=-(△φ)1/2(△R)3/D. (ⅲ) In a rhombically distorted octahedral 3d3 cluster.The paramagnetic systems are found to undergo the local axial distortions △Z and the planar bond angle variations △φ for K3Cr(CN)6 with K3Co(CN)6, K3Cr(CN)6 with K3Mn(CN)6 and K4V(CN)6·3H2O with K4Fe(CN)6·3H2O, respectively. Microscopically, the magnitudes of △Z and △φ can be conveniently illustrated by the axial (ADD) and perpendicular distortion degrees (PDD), respectively, for the paramagnetic systems with the corresponding diluents. (ⅳ) The electron paramagnetic resonance (EPR) g factors are quantitatively investigated for tetragonal Cu2+(2) site in Sr2Ca2Cu3Ox by utilizing the perturbation formulas of the g factors for a tetragonally elongated octahedral 3d9 cluster from the cluster approach. The anisotropy of the g factors is discussed from the local tetragonal elongation of this five-fold coordinated copper site.