Abstract
Iron tungstate (FeWO 4) and cobalt tungstate (CoWO 4) nanostructures were prepared by the hydrothermal method using sodium tungstate (Na 2WO 4·2H 2O), ferrous ammonium sulfate [(NH 4) 2Fe(SO 4) 2·6H 2O] and cobalt chloride (CoCl 2·6H 2O) solutions as precursors. The crystal structure and morphology of the as-prepared tungstates were characterized by X-ray diffraction analysis and transmission electron microscopy. The above characterizations render that the products obtained belong to the monoclinic crystal system and P2/a space group, with average sizes of nanoparticles of about 150 nm and 70 nm in the case of FeWO 4 and CoWO 4, respectively. Electronic properties of the FeWO 4 and CoWO 4 tungstates were studied using several X-ray spectroscopy methods, mainly X-ray photoelectron spectroscopy (XPS), X-ray emission spectroscopy (XES) and X-ray absorption spectroscopy (XAS). The XPS valence-band and core-level spectra, the XAS W L III edges (unoccupied W d-like states) as well as the XES bands reflecting the energy distribution of the valence W d- and O p-like states were recorded. The present XPS and XAS results reveal that the as-prepared FeWO 4 and CoWO 4 tungstates are in a composition close to a stoichiometric one. The XES results render that the W 5d- and O 2p-like states contribute throughout the whole valence-band region of the FeWO 4 and CoWO 4 tungstates, however maximum contributions of the O 2p-like states occur in the upper, whilst the W 5d-like states in the lower portions of the valence band, respectively.
Published Version
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