Ab initio investigation of structural and electronic properties of tungsten dioxide

Abstract

, Phone: þ375 172 938 869; Fax: þ375 172 938 869 A detailed study of electronic properties of tungsten dioxide (WO 2 ) has been performed by means of the projectoraugmented wave method. Two phases were considered: stable monoclinic, which was characterized as a metallic one, and high-temperature metastable orthorhombic, which was found to be a semiconductor with an energy gap of about 0.6 eV. We also show a possibility that oxygen vacancies in the monoclinic tungsten oxide providing the WO 1.75 stoichiometry can result in the semiconducting behaviour of this compound as well.

Visible–Near-Infrared-Light-Driven Oxygen Evolution Reaction with Noble-Metal-Free WO2–WO3 Hybrid Nanorods

“…It is probably attributed to the localized surface plasmon effects of metallic WO 2 . Apart from the main band gap (around 2.6 eV) of WO 2 –WO 3 nanorods, interestingly, a smaller band gap (around 0.7 eV) (Figure c) was also detected arising from the WO 2 material. ,, These results, therefore, are consistent with the W4f XPS measurement (Figure c), for example, the existence of reduced oxidation states W 5+ and W 4+ .…”

IR-Driven Photocatalytic Water Splitting with WO2–NaxWO3 Hybrid Conductor Material

“…Among the oxide conductor materials, WO 2 and Na x WO 3 ( x > 2.5) are two key tungstic metallic oxides. , Their energy band structures are shown in Figure (the conduction band and valence band of WO 2 are denoted as CB 1 and VB 1 , respectively; the conduction band and the intrinsic valence band of Na x WO 3 are denoted as CB 2 and VB 2–0 , respectively; the new energy level produced by Na doping of Na x WO 3 is denoted as VB 2–1 ). According to the energy band structure of WO 2 , its valence-band top and conduction-band minimum are located at −0.1 eV and −0.7 eV, respectively. Thus, the energy band structure of WO 2 is suitable for water reduction but not for water oxidation.…”

“…The IR-driven photocatalytic water splitting ability of the WO 2 –Na x WO 3 hybrid conductor material was suggested to owe to the formation of special ladder-type narrow energy band structures originating from the overlapping bands between the metallic WO 2 and Na x WO 3 (Figure ), , which is demonstrated by the valence-band energy XPS spectrum and upconversion luminescence. As shown in Figure , the valence-band energy XPS spectra of NaHTB-C900 showed three valence-band peaks (marked as VB 1 , VB 2–1 , and VB 2–0 ), located at approximately 0.0, 1.0, and 3.0 eV (vs Fermi level, corresponding to −0.1, 2.0, and 2.7 eV vs NHE), respectively, exhibiting a ladder-type valence-band energy structure.…”

Sodium Adsorption on the Surface of Thermally Oxidized Tungsten

“…The WO 2 oxide has the following main phases: a stable monoclinic phase and metastable orthorhombic one for high temperatures [12,13,18]. The calculation [14,15] of the electron density of the states shows that the valence band near the Fermi level is made of the O 2p and W 5d states, the band with the binding energy above 2.5 eV is mainly made of the O 2p states with a minor impurity of the W 5d states. At the same time, the valence band spectrum is wide -10 eV.…”