Phase separation in fluorite-related U 1– y Ce y O 2– x : new insights via variable temperature neutron diffraction
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Date
2024-09-01
Journal Title
Journal ISSN
Volume Title
Publisher
CEA
Abstract
The phase separation in the U1-yCey O2-x system for values of y between approximately 0.34 and 0.5 observed at low temperatures (below circa 600 K) purportedly involves only fluorite structures [1,3]. Therefore, to confirm this assumption it is logical to employ high resolution diffraction techniques that can track the progression of the oxygen-sub lattice and resolve peaks that may be overlapping. In this study, the phase separation in the U0.54Ce0.46O2-x system has been revisited using variable temperature high resolution neutron diffraction on samples that are sealed under Ar to prevent a change in oxidation state when heated.
As neutron scattering lengths for Unat and O do not differ to a large degree, U coherent cross section 8.903 barn vs O coherent cross section 4.232 barn, information about the oxygen sub lattice can be obtained from neutron diffraction patterns. This is not the case for X-ray diffraction which has been used for the bulk of the studies on this system.
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-x phase. Although the former is indeed a fluorite, we show that the other end-member phase has a C-type bixbyite structure, Figure 1. © The Authors
Description
Keywords
Fluorite, Neutron diffraction, Temperature range, Crystal lattices, Separation processes, Cross sections, Oxygen, X-ray diffraction, Substoichiometry, Cerium
Citation
Simeone, D., X., Garcia, P., Avdeev, M., Ablott, T., & Thorogood, G. J. (2024). Phase separation in fluorite-related U 1– y Ce y O 2– x : new insights via variable temperature neutron diffraction. Presentation to the 6th International ATALANTE Conference on Nuclear Chemistry for Sustainable Fuel Cycles (ATALANTE-2024) Avignon, France, September 1-6, 2024. In Book of Abstracts ATALANTE 2024 nuclear chemistry for sustainable fuel cycles, September 1-6, 2024 - Avignon, France, (pp. 111-112). Retrieved from: https://atalante2024.org/ATALANTE-2024-talks-BoA.pdf