STUDIES ON THE LOCAL STRUCTURE AND THE SPIN HAMILTONIAN PARAMETERS FOR THE TRIGONAL Mn2+ CENTER IN Bi4Ge3O12.

The local structure and the spin Hamiltonian parameters (the zero-field splitting D, the g factors g_//, g_⊥ and the hyperfine structure constants A_// and A_⊥) for the trigonal Mn²⁺ center in Bi₄Ge₃O₁₂ are theoretically studied from the perturbation formulas of these parameters for a 3d⁵ 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 Å towards the center of the oxygen octahedron along the C₃-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. [ABSTRACT FROM AUTHOR]