材料期刊网

The spin Hamiltonian (SH) parameters (g factors g (x) , g (y) and g (z) and the hyperfine structure constants A (x) , A (y) and A (z) ) and local structure for the rhombic Rh(4+) and Ir(4+) centers in TiO(2) (rutile) are theoretically studied from the perturbation formulas of these parameters for a low spin (S = 1/2) d (5) ion under rhombically distorted octahedra. In the calculations, the ligand orbital and spin-orbit coupling contributions as well as the influence of the local lattice distortions are taken into account using the cluster approach. The local axial elongation ratios are found to be about 1.7 and 3 times, respectively, larger for the Rh(4+) and Ir(4+) centers than that (a parts per thousand 0.0075) for the host Ti(4+) site in rutile, while the perpendicular distortion angles (a parts per thousand a'0.28A degrees and -0.42A degrees, respectively) are more than one order in magnitude smaller than the host value (a parts per thousand a'9.12A degrees). This means that the impurity centers exhibit further elongations of the oxygen octahedra and much smaller perpendicular rhombic distortions as compared with those of the host Ti(4+) site in TiO(2). The above local lattice distortions can be mainly ascribed to the substitution of the host Ti(4+) by the nd (5) impurities, which may induce different physical and chemical properties for the metal-ligand clusters. In addition, the influence of the Jahn-Teller effect on the local structure may not be completely excluded. The calculated SH parameters show reasonable agreement with the observed values.