One-dimensional uranium-organic coordination polymers: crystal and electronic structures of uranyl-diacetohydroxamate

Polymorphism and phase transitions in Na2U2O7 from density functional perturbation theory

Polymorphism and phase transitions in sodium diuranate, Na₂U₂O₇, are investigated with density functional perturbation theory (DFPT). Thermal properties of crystalline α-, β- and γ-Na₂U₂O₇ polymorphs are predicted from DFPT phonon calculations, i.e., the first time for the high-temperature γ-Na₂U₂O₇ phase (R3̄m symmetry). The standard molar isochoric heat capacities predicted within the quasi-harmonic approximation are for P2₁/a α-Na₂U₂O₇ and C2/m β-Na₂U₂O₇, respectively. Gibbs free energy calculations reveal that α-Na₂U₂O₇ (P2₁/a) and β-Na₂U₂O₇ (C2/m) are almost energetically degenerate at low temperature, with β-Na₂U₂O₇ becoming slightly more stable than α-Na₂U₂O₇ as temperature increases. These findings are consistent with XRD data showing a mixture of α and β phases after cooling of γ-Na₂U₂O₇ to room temperature and the observation of a sluggish α → β phase transition above ca. 600 K. A recently observed α-Na₂U₂O₇ structure with P2₁ symmetry is also shown to be metastable at low temperature. Based on Gibbs free energy, no direct β → γ solid-solid phase transition is predicted at high temperature, although some experiments reported the existence of such phase transition around 1348 K. This, along with recent experiments, suggests the occurrence of a multi-step process consisting of initial β-phase decomposition, followed by recrystallization into γ-phase as temperature increases.

BR, Sundararajan M, Ghanty TK, Sivaraman N. Remarkable structural effects on the complexation of actinides with H-phosphonates: a combined experimental and quantum chemical study

Strikingly novel effects on pH-modulated actinide extraction by branched H-phosphonates are investigated by solvent extraction combined with DFT.

Effects of preorganization in the chelation of UO22+by hydroxamate ligands: cyclic PIPO−vs.linear NMA−

Thanks to preorganization, 1,2-PIPOH, the six-membered ring cyclic hydroxamic acid, binds uranyl six times more strongly than its linear, methyl-substituted homolog (NMAH).

On the mechanical stability of uranyl peroxide hydrates: implications for nuclear fuel degradation

The mechanical properties and stability of studtite, (UO₂)(O₂)(H₂O)₂·2H₂O, and metastudtite, (UO₂)(O₂)(H₂O)₂, were investigated using density functional perturbation theory.