Pressure-induced evolution of the lattice dynamics for selected UO3 polymorphs

• Published in: Journal of nuclear materials 2023-10, Vol.584, p.154577, Article 154577
• Main Authors: Shields, Ashley E., Niedziela, J.L., Brubaker, Zachary, Spano, Tyler L., Isbill, Sara B., Kapsimalis, Roger J., Miskowiec, Andrew
• Format: Article
• Language: English
• Subjects: NUCLEAR FUEL CYCLE AND FUEL MATERIALS
• ISSN: 0022-3115; 1873-4820
• DOI: 10.1016/j.jnucmat.2023.154577

•Four phases of UO3 investigated up to 45 GPa with density functional theory.•Two phases exhibit isotropic response to pressure; two an anisotropic response.•Eigenvector decomposition tracks changes in coordination environment via phonon modes. Uranium trioxide (UO3) is a stable chemical form of uranium oxide with multiple polymorphs found throughout the nuclear fuel cycle. The pressure-induced changes in the structure and lattice dynamics of four of these polymorphs are simulated with density functional perturbation theory and analyzed. Two phases, α- and δ-UO3 are found to exhibit an isotropic response to pressure and do not undergo any changes in coordination geometry up to ∼40 GPa. In contrast, the other two phases investigated, β- and γ-UO3, exhibit an anisotropic response to pressure. Decomposition of the phonon eigenvectors allows us to assign specific pressure-induced structural changes to individual phonon modes. This analysis has been performed on a per atom basis for the relatively simple α- and δ-UO3 structures, which have one symmetrically unique uranium site, and on a per coordination environment basis for β- and γ-UO3, which have multiple U sites.