材料期刊网

The local structures and the spin Hamiltonian parameters for the substitutional Nb(4+) centers in MO(2) (M = Sn, Ti and Ge) crystals are theoretically studied using the perturbation formulas of these parameters for a 4d(1) ion in a rhombically compressed octahedron. The above Nb(4+) centers are found to experience the Jahn-Teller distortions, characteristic of the relative axial compressions (similar to 0.01-0.02 angstrom) and the non-axial (planar) angular increases (similar to 3 degrees). As a result, the ligand octahedra are transformed from original elongation on host tetravalent cation sites to compression in the impurity centers, with additional non-axial distortions smaller than those in the hosts. The influences of the,Jahn-Teller distortions and the ligand orbital contributions are also analyzed.