Research on the Spin-Hamiltonian Parameters and Local Structure for the Tetragonal Mo5+ Centers in CaWO4 Crystal

The spin-Hamiltonian parameters (g factors g(parallel to) g(perpendicular to) and hyperfine structure constants A(parallel to) (A),A(perpendicular to) (A), A(parallel to) (B) and A(perpendicular to) (B), A(A) and A(B) belonging to isotopes Mo-95(5+) and Mo-97(5+)) of Mo5+ ion at the tetragonally-compressed tetrahedral W6+ site in CaWO4 crystal are calculated from the high-order perturbation formulae based on the two-mechanism model, where besides the contributions to spin-Hamiltonian parameters due to the crystal-field mechanism concerning the crystal-field excited states in the extensively-applied crystal-field theory, those due to charge-transfer mechanism concerning charge-transfer excited states (which are omitted in crystal-field theory) are included. The calculated results are in reasonable agreement with the experimental values. The calculations show that for the high-valence state d(n) ions (e. g., Mo5+ considered) in crystals, the contributions due to charge-transfer mechanism should be taken into account in the studies of spin-Hamiltonian parameters. The local structure of Mo5+ center in CaWO4 crystal due to the impurity-induced local lattice relaxation is estimated from the calculations. The results are discussed.