Investigations on the EPR parameters and local structures for the substitutional Ti³⁺ and W⁵⁺ centers in stishovite

Local structures and electron paramagnetic resonance (EPR) parameters (g factors g _x , g _y , and g _z ) for the substitutional Ti³⁺ and W⁵⁺ centers in stishovite are theoretically investigated by using the high-order perturbation formulas of these parameters for a d¹ ion in rhombically compressed octahedra. In the calculation formulas, the related molecular orbital coefficients are obtained from the cluster approach, and the relevant crystal-field (CF) parameters are determined from the superposition model, which enables to connect these CF parameters and, hence, the studied g factors with the local structures of the Ti³⁺ and W⁵⁺ centers in stishovite. Based on the calculations, the impurity–ligand bond lengths parallel and perpendicular to the C ₂-axis are found to be R′_|| (≈1.751 and 1.717 Å) and R′_⊥ (≈1.788 and 1.806 Å) with the planar bond angles θ′ (≈89.0° and 88.2°) for the studied [TiO₆]⁹⁻ and [WO₆]⁷⁻ clusters, respectively. The calculated results are in good agreement with the experimental data, and the validity of the results is discussed.