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The local structures of the two rhombic Ni3+ centers (on the substitutional and interstitial sites) in rutile (TiO2) are theoretically studied from the perturbation formulas of the g factors for a 3d(7) 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 are 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 Delta alpha(s) approximate to -1.09 degrees) than that (Delta alpha(H)(s) approximate to -0.73 degrees) in the host and the much smaller perpendicular distortion (characterized by the rhombic distortion angle Delta theta(s) approximate to -0.75 degrees) than that (Delta alpha(H)(s) approximate to -9.0 degrees) in the host due to the Jahn-Teller effect. For the interstitial Ni3+ center, the ligand octahedron is found to undergo a smaller compression (characterized by the axial distortion angle Delta alpha(i) approximate to 1.48 degrees) than that (Delta alpha(H)(i) approximate to 8.17 degrees) in the host and a slighter rhombic distortion (Delta theta(i) approximate to 0.1 degrees) than that (Delta theta(H)(i) approximate to 7.0 degrees) in the host due to the Jahn-Teller effect. The calculated g factors based on the above structural parameters show better agreement than those based on the host structural parameters and those in absence of the spin-orbit coupling and the orbitals of the ligands with the experimentally observed values. (c) 2006 Elsevier B.V. All rights reserved.