材料期刊网

The local structure and the EPR parameters (zero-field splitting D, g factors g(parallel to) and g(perpendicular to) and hyperfine structure constants A(parallel to) andA(perpendicular to)) of Mn4+ in LiF:U:Mn crystal have theoretically been investigated by using the perturbation formulas of the EPR parameters for a 3d(3) ion in trigonally distorted octahedra. In this trigonal Mn4+ center, three U6+ ions locate on (1,1,0), (1,0,1) and (0,1,1) sites, each surrounded by Six O2- ions. Thus, the studied system is characterized as the Mn4+ associated with one host F- triangle, one O2- triangle and an additional equivalent F-,F-- triangle containing the three U6+ ions, i.e. an [MnF3O3F'(3)](8-) cluster. The central Mn4+ impurity is found to shift towards the oxygen triangle along the C-3 (or [111]) axis by an amount DeltaZ (approximate to 0.29 Angstrom) due to the strong electrostatic attraction between the Mn4+ and the oxygen triangle (and also the additional equivalent F-,F-- triangle), which increases the trigonal distortion of the Mn4+ center considerably. The calculated EPR parameters based on the above displacement DeltaZ agree reasonably with the observed values.