Influence of the Crystal-Field Potential on Interionic Separation in Salts of Divalent Iron-Group Ions

Abstract

The crystal energies of ionic lattices containing iron group ions with nonspherically symmetric electronic ground states are appreciably lowered as a result of crystal field splitting of the lowest energy levels. This gives rise to a characteristic periodic variation of the equilibrium cation‐anion separation as the 3d shell is progressively filled. It is possible to estimate the contractions of interionic separation resulting from the crystal field effect by comparison with the distances in lattices containing only ions with S ground states. In the divalent oxides and halides, these contractions are of the order of 0.04–0.22 A. By treating the crystal‐field stabilization as a small perturbation, the contractions can be calculated for simple lattice structures. Good agreement between theory and experiment is found for oxides crystallizing in the sodium chloride lattice, with the exception of VO. The lattice contractions of D_3d³ iodides and D_4h¹⁴ fluorides can also be consistently correlated with stabilization energy in these salts.