Low-temperature absorption spectrum of the nickel(II) ion in single crystals of the columbite NiNb2O6

Abstract

The ligand-field spectrum of Ni^II in NiNb₂O₆ crystals has been investigated in the range 5000–30 000 cm^–1 at temperatures from 300 to 4.2 K. The spectra were measured using polarized light with the electric vector parallel to all three crystallographic axes. The spilittings and intensities of the bands are interpreted in terms of a major C_2ν and a minor C₂ perturbation of the octahedral site. Most of the observed intensity is derived from the static low-symmetry distortion, but the effects of spin–orbit coupling and of vibronic interactions are also taken into account. The spectrum is remarkably similar to that of Ni^II in the structurally related wolframites MWO₄(M = Mg, Zn, Cd).