Intermediate-spin state of a 3D ion in the octahedral environment and generalization of the Tanabe - Sugano diagrams

摘要

Electronic spectra of 3d~n transition ions in an octahedral ligand surrounding have been studied using the modified crystal field approach (MCFA), which includes a relativistic spin - orbital interaction. A new variable parameter, the effective nuclear charge Z_(eff) of a metal ion that allows accounting implicitly the covalence degree of a metal - ligand bond, has been introduced. Energy diagrams similar to the Tanabe - Sugano ones have been calculated. To study the spin state evolution of the metal ion in an arbitrary distorted octahedral complex, a spin state diagram approach has been proposed. The intermediate-spin (IS) state problem for 3d~4, 3d~5, and 3d~6 metal ions has been considered and conditions for the IS state realization have been formulated. The regions of the mixed high-, intermediate-, and low-spin states have been found. The possibility of coexistence of the different spin states of 3d ions in the octahedral complexes has been considered using crystallography data for the YBaCo_2O_(5.5) layered cobaltite.