Electronic structure of FeWO4 and CoWO4 tungstates: First-principles FP-LAPW calculations and X-ray spectroscopy studies

Total and partial densities of states of the constituent atoms of iron tungstate, FeWO4, and cobalt tungstate, CoWO4, 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 FeWO4 and CoWO4 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 FeWO4 and CoWO4 compounds. Other significant contributors into the valence-band region are the Fe 3d- and W 5d-like states in FeWO4 and the Co 3d- and W 5d-like states in CoWO4. 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 FeWO4 and CoWO4 compounds.