The electronic spectrum of NiTa 2O 6

Abstract

The polarized absorption spectrum of single crystals of NiTa 2O 6 has been measured from 6000 to 28 000 cm −1 at various temperatures from 300 to 10 K. All the observed absorption regions are due to electronic transitions mainly localized on the Ni 2+ ions. The first band system in the region 6000–10500 cm −1 corresponds to a transition which occurs mainly by magnetic dipole mechanism. The band systems in the other regions are due to vibronic transitions. By applying our method of analysis of the site geometry based on symmetry descent, we deduce that the O h → D 2 h distortion of NiO 6 n− can be decomposed into two contributions related to the steps O h → D 4 h and D 4 h → D 2 h and that the second contribution is much larger than the first. Successively we give an explanation for most of the features of the spectra by considering only the D 4 h → D 2 h perturbation and the vibronic interactions. The effect of the spin-orbit coupling has also been considered.