Electronic structure of hexagonal tungsten trioxide: XPS, XES, and XAS studies

X-Ray photoelectron (XPS), emission (XES) and absorption (XAS) spectroscopy methods were used to study the electronic structure of hexagonal tungsten trioxide, h-WO3. Its precursor, hexagonal hydrogen tungsten bronze, HxWO3, and the monoclinic form of tungsten trioxide, m-WO3, were also studied. For the mentioned compounds, both the XPS valence-band and core-level spectra, as well as the O K alpha emission bands and the W L-111 absorption edges w ere derived. It was established that, binding energies of both the W 4f and O 1 s core-level electrons do not change when going from the tungsten trio xides to HxWO3. A high-energy shift of the inflection point of the XAS W L- 111 spectrum of the HxWO3 bronze, with respect to its position on the spect rum of pure metallic tungsten, was found to be close to those of the spectr a of the two WO3 forms studied. Half-widths of both the XPS valence-band sp ectra and the O K alpha hands increase somewhat in the sequence m-WO3-->h-W O3-->HxWO3. The formation of a near-Fermi sub-band, which is absent for bot h the modifications of WO,, was observed on the XPS valence-band spectrum o f hexagonal H,WO,. The energy positions of the centers of gravity of the O K alpha band remain constant for all the compounds studied. (C) 2001 Elsevi er Science B.V. All rights reserved.