Electronic structure of CuWO 4: XPS, XES and NEXAFS studies

Abstract

X-ray photoelectron spectroscopy (XPS), X-ray emission spectroscopy (XES) and near-edge X-ray absorption fine structure (NEXAFS) methods were applied to study the electronic structure of copper tungstate, CuWO 4. For the compound, XP valence-band spectra with different energies of excitation were studied, as well as the XE O Kα band and the NEXAFS O 1s spectrum were derived. The binding energies of the XP core-level electrons of the constituting elements of CuWO 4 were measured. For comparison, some spectra of the hexagonal form of tungsten trioxide, h-WO 3, were investigated. It was found that the half-width of the O Kα band decreases somewhat but that of the XP valence-band spectrum increases when going from h-WO 3 to CuWO 4, however the energy positions of the maxima and of the centres of gravity of the O Kα band remain constant for the above compounds. Measurements of the XP O 1s core-level binding energies and of the energy positions of the inflection point of the NEXAFS O 1s spectra reveal that the effective negative charge of oxygen atoms in CuWO 4 is close to that in h-WO 3, while XPS W 4f core-level measurements reveal that the positive effective charge of tungsten atoms decreases somewhat in the sequence h-WO 3 → CuWO 4.