材料期刊网

The local structure and the spin Hamiltonian parameters (the zero-field splitting D, the g factors g parallel to, g perpendicular to and the hyperfine structure constants A// and A perpendicular to) for the trigonal Mn2+ center in Bi4Ge3O12 are theoretically studied from the perturbation formulas of these parameters for a 3d(5) ion in trigonal symmetry. The impurity Mn2+ replacing host Bi3+ is not found to occupy the exact Bi3+ site but to suffer a large off-center displacement by about 0.36 angstrom towards the center of the oxygen octahedron along the C-3-axis due to the size and charge mismatching substitution. The calculated spin Hamiltonian parameters based on the above displacement show good agreement with the observed values. The results and the mechanism of the impurity displacement are discussed.