The local structures of the two rhombic Ni3+ centers (on the substitutional and interstitial sites) in rutile (TiO2) were theoretically studied from the perturbation formulas of the g factors for a 3d7 ion of low spin (S = 1/2) in rhombically distorted octahedra. In these formulas, the contributions to the g factors from the low symmetrical parts of the crystal-fields as well as the spin-orbit coupling interaction and orbitals of the ligands were taken into account. From the investigations, the ligand octahedron in the substitutional Ni3+ center may suffer a slightly larger axial elongation (characterized by the axial distortion angle Δαs ≈ -1.09°) than that (ΔαsH ≈ -0.73°) in the host and the much smaller perpendicular distortion (characterized by the rhombic distortion angle Δθs ≈ -0.75°) than that (ΔθsH ≈ -9.0°) in the host due to the Jahn-Teller effect. For the interstitial Ni3+ center, the ligand octahedron was found to undergo a smaller compression (characterized by the axial distortion angle Δαi ≈ 1.48°) than that (ΔαiH ≈ 8.17°) in the host and a slighter rhombic distortion (Δθi ≈ 0.1°) than that (ΔθiH ≈ 7.0 °) in the host due to the Jahn-Teller effect. The calculated g factors based on the above structural parameters gave better agreement than did those based on the host structural parameters and those in the absence of the spin-orbit coupling and the orbitals of the ligands with the experimentally observed values.

Studies on the Local Structures of the Substitutional and Interstitial Ni3+ Centers in Rutile. Wu, S.Y., Gao, X.Y., Lin, J.Z., Fu, Q., Lu, G.D.: Chemical Physics, 2006, 328[1-3], 26-32