The band structure of WO3 and non-rigid-band behaviour in Na0.67WO3 derived from soft x-ray spectroscopy and density functional theory

B. Chen, J. Laverock, L. F.J. Piper, A. R.H. Preston, S. W. Cho, A. Demasi, K. E. Smith, D. O. Scanlon, G. W. Watson, R. G. Egdell, P. A. Glans, J. H. Guo

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The electronic structure of single-crystal WO3 and Na 0.67WO3 (a sodium-tungsten bronze) has been measured using soft x-ray absorption and resonant soft x-ray emission oxygen K-edge spectroscopies. The spectral features show clear differences in energy and intensity between WO3 and Na0.67WO3. The x-ray emission spectrum of metallic Na0.67WO3 terminates in a distinct Fermi edge. The rigid-band model fails to explain the electronic structure of Na0.67WO3 in terms of a simple addition of electrons to the conduction band of WO3. Instead, Na bonding and Na 3s-O 2p hybridization need to be considered for the sodium-tungsten bronze, along with occupation of the bottom of the conduction band. Furthermore, the anisotropy in the band structure of monoclinic γ-WO3 revealed by the experimental spectra with orbital-resolved geometry is explained via density functional theory calculations. For γ-WO3 itself, good agreement is found between the experimental O K-edge spectra and the theoretical partial density of states of O 2p orbitals. Indirect and direct bandgaps of insulating WO3 are determined from extrapolating separations between spectral leading edges and accounting for the core-hole energy shift in the absorption process. The O 2p non-bonding states show upward band dispersion as a function of incident photon energy for both compounds, which is explained using the calculated band structure and experimental geometry.

Original languageEnglish
Article number165501
JournalJournal of Physics Condensed Matter
Issue number16
Publication statusPublished - 2013 Apr 24

All Science Journal Classification (ASJC) codes

  • Materials Science(all)
  • Condensed Matter Physics


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