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Surface oxidation of (110)-oriented UO(2) single crystals leached in demineralized water at 180 C for 24 hours has been studied by means of the backscattering/channelling technique. The O sublattice was analyzed using the (16)O((4)He, (4)He)(16)O resonance occurring at 3045 keV. Quasiepitaxial growth of an oxidized surface layer was observed and attributed to the phase transformation from the cubic UO(2) to a monoclinic UO(r) phase with r = 2.28±0.05. X-ray diffractometry was also used to study the orientation of (110) atomic planes of the transformed layer with respect to the bulk crystal and to measure the change of the (110) interplane distance. A simple geometrical model of the quasiepitaxial growth is proposed and the distortion of the UO(2) cubic elementary cell due to the incorporation of surplus oxygen atoms is determined. Monte Carlo simulations of channelling data confirm the model and provide indications about atom location. The observed monoclinic phase is compared with other phases of uranium oxides.

Additional information

Authors: NOWICKI L ET AL, Soltan Institute for Nuclear Studies, Warsaw (PL);CHOFFEL C ET AL, Centre de Spectrométrie Nucléaire et de Spectrométrie de Masse, Orsay (FR);GACA J ET AL, Institute of Electronic Materials Technology, Warsaw (PL);MATZKE H, JRC Karlsruhe (DE)
Bibliographic Reference: Article: Physical Review B, Vol. 56 (1997) No. 2, pp. 534-542
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