Electronic structure of FeWO 4 and CoWO 4 tungstates: First-principles FP-LAPW calculations and X-ray spectroscopy studies

Abstract

Total and partial densities of states of the constituent atoms of iron tungstate, FeWO 4, and cobalt tungstate, CoWO 4, have been calculated using the first-principles self-consistent full potential linearized augmented plane wave (FP-LAPW) method. The results obtained reveal that the O 2p-like states are the dominant contributors into the valence band of the tungstates under consideration, whilst the bottom of the conduction band of FeWO 4 and CoWO 4 is dominated by contributions of the empty Fe 3d- and Co 3d-like states, respectively. The FP-LAPW data indicate that the O 2p-like states contribute mainly into the top of the valence band, with also significant contributions throughout the whole valence-band region, of FeWO 4 and CoWO 4 compounds. Other significant contributors into the valence-band region are the Fe 3d- and W 5d-like states in FeWO 4 and the Co 3d- and W 5d-like states in CoWO 4. All the above d-like states contribute throughout the whole valence-band region of the tungstates under consideration, however maximum contributions of the W 5d-like states occur in the lower, whilst the Fe (Co) 3d-like states in the upper portions of the valence band, respectively. To verify the above FP-LAPW data, the X-ray emission bands representing the energy distributions of mainly the valence O p-, Fe (Co) d-, Fe (Co) p- and W d-like states were measured and compared on a common energy scale with the X-ray photoelectron valence-band spectrum of the corresponding tungstate. The experimental data were found to be in good agreement with the theoretical FP-LAPW results for the electronic structure of FeWO 4 and CoWO 4 compounds.