ELECTRONIC STRUCTURE OF H_YWO_3 AND WO_x STUDIED BY THE XPS, XES, AND XAS METHODS

摘要

X-Ray photoelectron (XPS), emission (XES), and absorption (XAS) spectroscopy methods have been used to study the electronic structure of the compounds H_tWO_3 (y=0.24) and WO_x (2.0 ≤ x ≤ 3.0). The XPS core-level binding energies (BE's) and valence-band structures for the above compounds have been determined. The XES O K_α and XAS W L_(Ⅲ) spectra for the compounds H_(0.24)WO_3 and WO_x have been derived. In all the tungsten oxides studied the energy positions of the centers of gravity of the O 2p-like emission bands remain constant. Halfwidths of both the XPS W 4f and O 1s core-level spectra increase in the sequence WO_3 → WO_2. The creation of a subband of M―M-interactions with a two-peak structure in the near-Fermi region of the XPS valence-band spectra has been observed for WO_x, where 2.0 ≤ x ≤ 2.77. The above subband intensity significantly increased in the sequence WO_(2.77) → WO_(2.3) → WO_2. The XPS O 1s core-level BE's remain constant (within the experimental error) for the hydrogen tungsten bronze H_(0.24)WO_3 and all the tungsten oxides studied. The O K_α band halfwidth somewhat increases going from the tungsten oxides WO_x to the compound H_(0.24)WO_3. It was established that, charge states of the tungsten and oxygen atoms in the H_(0.24)WO_3 compound are close to those in the tungsten trioxide WO_3. The inflection point of the W L_(Ⅲ) absorption spectra shifted monotonously towards the higher energies going from WO_2 to WO_3.