Studies of EPR theory and trigonal distortion of the (NiX6)4− clusters (X = halide ion) in the series of perovskite crystals AMX3 (A = Rb, Cs; M = Cd, Mg; X = halide ion)

A theoretical method is shown to yield a detailed explanation of numerous EPR parameters for d8 configuration ion in trigonal ligand field. On the basis of the complete energy matrix, the local lattice structures of the octahedral (NiX6)4− clusters in the series of perovskite crystals AMX3 (A = Rb, Cs; M = Cd, Mg; X = Cl, Br, I) with D3d site symmetry have been studied by simulating the EPR and optical spectra. Moreover, the influences of the local lattice structure parameters R and θ as well as the spin-orbit coupling coefficient ζ on the ZFS parameter D from different systems are discussed.