The crystal structure of U3O7: Refinement of oxygen positions from neutron diffraction data
Uranium(IV) oxide (UO2) shows a tendency to oxidize when exposed to oxidizing compounds, but conversion to the thermodynamically more stable oxide U3O8 is usually undesirable because it is associated with a structure modification and volume expansion of about 36%. Oxidation of UO2 is a complex process involving long-range ordering of oxygen clusters in a fluorite-type parent structure. We focus here on the intermediate oxide U3O7, which is the last phase based on this arrangement before the transition to U3O8 occurs. Recently our group performed electron diffraction experiments on a U3O7 sample prepared at thermal equilibrium. The results allowed to unambiguously assign the symmetry involved in its long-range ordered structure. The proposed structural model, however, is different from the model derived from earlier neutron diffraction experiments which were performed in out-of-equilibrium conditions during the isothermal oxidation of a UO2 sample. Accurately collected neutron diffraction data on a set of U3O7 samples are essential to further refine the structural model, and to understand the transition to U3O8 in the oxidation process.
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LEINDERS Gregory; BALDINOZZI Gianguido; LAMOEN Dirk; RITTER Clemens; SCHREINEMACHERS Christian; SUARD Emmanuelle and VERWERFT Marc. (2019). The crystal structure of U3O7: Refinement of oxygen positions from neutron diffraction data. Institut Laue-Langevin (ILL) doi:10.5291/ILL-DATA.5-21-1119
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