X-ray photoelectron spectroscopy of the uranium/oxygen system

Other authors have presented evidence to show that the oxidised surface layer which forms on UO2 at 250C is amorphous UO3. In the present study X-ray photoelectron spectroscopy, infra-red spectroscopy and X-ray diffraction have been used to characterise the higher oxides α-UO3, β-UO3, γ-UO3 and δ-UO3. While the infra-red and X-ray diffraction results may be used to characterise each oxide the X-ray photoelectron spectra for each phase are very similar. During reduction of the oxide surface in the spectrometer changes in the spectra were observed which were shown to be associated with particular oxidation states of the metal rather than different uranium atom coordination sites within the oxide. A close structural relationship is demonstrated between these oxides and the product at the surface of air-oxidised UO2 fuel. (author)