The EPR 𝑔 factors $g_{i}$ $(i = x, y, z)$ for the interstitial Ti³⁺ in rutile are theoretically studied from the perturbation formulas of these parameters for a 3d¹ 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 $(\approx 0.026)$ and the rhombic distortion angle $\delta \phi'$ $(\approx 0.7^{\circ})$ around the impurity Ti³⁺ are smaller than the host values ($\approx 0.091$ 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 Ti³⁺ center are also reasonably interpreted.

The 𝑔 factors and the ligand superhyperfine parameters $A'$ and $B'$ for Ni³⁺ in KMgF₃, CsCaF₃ and RbCaF₃ are theoretically studied from the formulas of these parameters for a 3d⁷ ion under octahedral environments in the weak field scheme. The unpaired spin densities for the fluorine 2s, 2p$_{\sigma}$ and 2p$_{\pi}$ 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:Ni³⁺ are satisfactorily interpreted from the different impurity–ligand distances due to the elongation of the ligand octahedron during cubic-to-tetragonal phase transition.