Theoretical study of local lattice structure of Fe3+-V cd and Fe3+-Li+ systems in RbCdF3 and CsCdF3 crystals

A theoretical method for investigating the inter-relation between the electronic and the molecular structures of a 3d5 ion in a tetragonal ligand-field has been established on the basis of a 252×252 complete energy matrix. By means of this method, the local structure of the Fe3+-V cd and Fe3+-Li+ systems in RbCdF3:Fe3+ and CsCdF3:Fe3+ crystals are determined by the experimental EPR spectrum. Our calculation show that the local lattice structure around an octahedral Fe3+ center has a compression distortion along the crystalline axis in RbCdF3 as well as in CsCdF3 crystals, and that the compression magnitude of a tetragonal Fe3+-Li+ system is larger than that of the Fe3+-V cd system. This may be ascribed to the fact that a Fe3+ ion replaces a Cd2+ ion and a Li+ ion substitutes for another Cd2+ ion next to the Fe3+ ion in the Fe3+-Li+ system, and the Li+ ion will shift to the Fe3+ ion, which pushes the F1 ion toward the Fe3+ ion. Using this method, the experimental EPR parameters b20, b40 and b44 are also interpreted simultaneously.