Theoretical study of local lattice structure of Mn2+ in perovskite fluorides A2MF4 (A=K, Rb; M=Mg, Zn, Cd) series

A theoretical method for investigating the inter-relation between the molecular structure and electronic structure has been established on the basis of the 252×252 complete energy matrices for a 3d5 configuration ion in a tetragonal ligand field. By means of this method, which is independent of the X-ray diffraction, the local structure of the paramagnetic Mn2+ ion in perovskite fluorides A2MF4 (A=K, Rb; M=Zn, Mg, Cd) are determined directly by analyzing the EPR spectrum of octahedral Mn2+ center in A2MF4 crystals and the optical absorption spectrum of the (MnF6)4− cluster. It is shown that, comparing with the octahedral cubic structure, the local micro-structure in the vicinity of Mn2+ displays an elongated distortion when b20>0 and a compressed distortion when b20<0, and ΔR   vs. 104b20 as well as ΔR   vs. 104b40 in the distortion region is, respectively, approximately linear. Simultaneously, the theoretical zero-field-splitting parameters b20, b40 and b44 are in good agreement with the experimental values.