材料期刊网

The anisotropic g factors (gx, gy, gz) at low temperature and the motionally averaged isotropic g factor at high temperature for two Cr5+ centers, the tetragonal t-Cr5+ center and the rhombic O-Cr5+ center, in ferroelectric PbTiO3 are calculated from the high-order perturbation formulas based on a two-mechanism model. In the model, the contributions to g factors from both the crystal-field (CF) mechanism concerning the CF excited states and the charge-transfer (CT) mechanism (which is neglected in CF theory) concerning the CT excited states are contained. The calculated results are in reasonable agreement with the experimental values. From the calculations, the defect models of t-Cr5+ center (which is attributed to Cr5+ in the tetragonally-compressed octahedron caused by Jahn-Teller effect rather than in the tetragonally-elongated octahedron in the host PbTiO3) and O-Cr5+ center (which is due to the t-Cr5+ center perturbated by the electrical polarization perpendicular to the C4 axis) are confirmed, and the defect structure of t-Cr5+ center is obtained. It is found that in the precise calculations of g factors for the high valence state d1 ions in crystals, both the contributions due to CF and CT mechanisms should be taken into account. (c) 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)