The EPR g factors g i (i = x, y, z) for the interstitial Ti 3+ in rutile are theoretically studied from the perturbation formulas of these parameters for a 3d 1 ion in rhombically compressed octahedra. The ligand octahedron in the impurity center is found to be less compressed than that on the host interstitial site due to the Jahn-Teller effect. The local compression parameter (≈0.026) and the rhombic distortion angle δφ (≈0.7 • ) around the impurity Ti 3+ are smaller than the host values (≈0.091 and 3.5 • ). The theoretical g factors based on the above local structural parameters are in good agreement with the experimental data. In addition, the g factors for a tetragonal interstitial Ti 3+ center are also reasonably interpreted.

The superhyperfine parameters T j ( j = x, y, z) for Cu 2+ in the squareplanar K 2 PdX 4 (X = Cl, Br) are theoretically studied from the perturbation formulas of these parameters for an octahedral 3d 9 cluster, by considering both the contributions from the crystal-field and charge-transfer mechanisms. The related molecular orbital coefficients are determined from the cluster approach in a uniform way. Based on one adjustable proportional factor ρ for the orbital admixture coefficients, the calculated results of present work show reasonable agreement with the observed values.Keywords Electron paramagnetic resonance (EPR) · Superhyperfine interactions · Cu 2+ · K 2 PdX 4 (X = Cl, Br)

The g factors and the ligand superhyperfine parameters A and B for Ni 3+ in KMgF3, CsCaF3 and RbCaF3 are theoretically studied from the formulas of these parameters for a 3d 7 ion under octahedral environments in the weak field scheme. The unpaired spin densities for the fluorine 2s, 2pσ and 2pπ orbitals are quantitatively determined from the molecular orbital and configuration interaction coefficients based on the cluster approach. The calculated results show good agreement with the experimental data, based on only one adjustable parameter (i.e., the proportionality factor ρ related to the ligand s-and p-orbitals). The superhyperfine parameters for the axial and planar ligands in RbCaF3:Ni 3+ are satisfactorily interpreted from the different impurity-ligand distances due to the elongation of the ligand octahedron during cubic-to-tetragonal phase transition.

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