Spin-Hamiltonian parameters and defect structure for the tetragonal Mo5+ center in the reduced BaTiO3:Mo crystal

The spin-Hamiltonian parameters (g factors g(parallel to), g(perpendicular to) and hyperfine structure constants A(parallel to), A(perpendicular to)) of the tetragonal Mo5+ center in reduced BaTiO3:Mo crystal with low temperature phase are calculated from the high-order perturbation formulas based on the two-mechanism model for d(1) ions in octahedral clusters with the ground state B-2(2) (vertical bar d(xy)>). In the model, both the contributions to spin-Hamiltonian parameters from the crystal-field (CF) mechanism and that from the charge-transfer (CT) mechanism (which is neglected in the widely-used crystal field theory) are considered. The calculated results are in reasonably agreement with the experimental values. The calculations show that for the spin-Hamiltonian parameters of BaTiO3:Mo5+, the relative importances of CT mechanism vertical bar Q(CT)/Q(CF)vertical bar are about 17%, 9%, 7% and 7% for Q=Delta g(parallel to), Delta g(perpendicular to), A(parallel to)((2)), and A(perpendicular to)((2)) (where Delta g=g-g(e), g(e) approximate to 2.0023, the g factor of free electron), respectively. It appears that for the high valence state d(n) ion clusters in crystals, the precise and complete calculations of spin-Hamiltonian parameters should take both the CF and CT mechanisms into account. The tetragonally-compressed distortion of (MoO6)(7-) octahedral clusters in the low-temperature rhombohedral phase of BaTiO3 caused by the static Jahn-Teller effect is also acquired from the calculations. The results are discussed. (c) 2013 Elsevier B.V. All rights reserved.