Studies of the local phase-transition behaviour for Ni+-II centers in RbCaF3 crystal from EPR data

By fitting the calculated EPR g(i)(i = x, y, z) factors to the observed val ues, the local release factor k(l) which is introduced to characterize the release (or elongation) effect of impurity-ligand bonds along the rotationa l axis in the cubic-to-tetragonal phase transition of ABX(3) perovskites, i s obtained for the Ni+-II center in RbCaF3 crystal. The result shows that, similar to the local rotational angle (or order parameter) phi, the local r elease factor is unlike that of the host crystal. It suggests that in the d oped crystal the impurity can affect the local phase transition behaviour i n the vicinity of impurity ions.