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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.
Inorganic Chemistry
|August 20, 2019
Summary
Phase separation in uranium-cerium oxide systems below 600 K involves two structures. Reexamination confirms a fluorite phase and an oxygen-deficient bixbyite phase, suggesting bixbyite structure across cerium compositions.
Area of Science:
- Materials Science
- Solid State Chemistry
- Crystallography
Background:
- Phase separation in U1-xCexO2-y systems is crucial for understanding material behavior.
- Previous studies suggested only fluorite structures in the miscibility gap below 600 K for specific compositions.
- An oxygen-deficient C-type bixbyite structure was reported for higher cerium content (y > 0.5).
Purpose of the Study:
- To reexamine the phase separation in U0.54Ce0.46O2-y using advanced diffraction techniques.
- To clarify the structural nature of the phases present in the miscibility gap.
- To determine if the oxygen-deficient phase exhibits a bixbyite structure across the cerium composition range.
Main Methods:
- X-ray diffraction analysis.
- Neutron diffraction analysis.
- Crystallographic structure determination.
Main Results:
- Confirmed the existence of two fluorite-related structures in the miscibility gap below a critical temperature.
- Identified a stoichiometric U0.54Ce0.46O2 phase with a fluorite structure.
- Showed that the oxygen-deficient U0.54Ce0.46O2-y phase possesses a C-type bixbyite structure.
Conclusions:
- The oxygen-deficient phase in the U-Ce-O system exhibits a C-type bixbyite structure.
- This finding suggests that the bixbyite structure can describe the oxygen-deficient phase across the entire cerium composition range.
- The study refines the understanding of phase equilibria and structural characteristics in uranium-cerium oxide solid solutions.
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