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Phase Separation in Fluorite-Related U1-CeO2-: A Re-Examination by X-ray and Neutron Diffraction
David Simeone1,2, Philippe Garcia3, Audrey Miard3
1CEA/DEN/DMN/SRMA/LA2M-LRC CARMEN, CEA , Université Paris-Saclay , F-91191 Gif-sur-Yvette , France.
Abstract:
The phase separation observed at low temperature (below circa 600 K) in the U1-CeO2- system and for values of y between roughly 0.34 and 0.5 purportedly involves fluorite structures only. However, for y values above 0.5, an oxygen-deficient C-type bixbyite is also reported. In this work, the phase separation in U0.54Ce0.46O2- has been reexamined using X-ray and neutron diffraction. Below a critical temperature, the existence of two fluorite related structures in the miscibility gap is confirmed: a stoichiometric U0.54Ce0.46O2 phase and an oxygen-deficient U0.54Ce0.46O2- phase. Although the former is indeed a fluorite, we show that the other end-member phase has a C-type bixbyite structure. This would suggest that the oxygen-deficient phase can be described as a bixbyite over the entire cerium composition range.
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