A New Look at the Structural Properties of Trisodium Uranate Na₃UO₄

Abstract

The crystal structure of trisodium uranate, which forms following the interaction between sodium and hyperstoichiometric urania, has been solved for the first time using powder X-ray and neutron diffraction, X-ray absorption near-edge structure spectroscopy, and solid-state (23)Na multiquantum magic angle spinning nuclear magnetic resonance. The compound, isostructural with Na3BiO4, has monoclinic symmetry, in space group P2/c. Moreover, it has been shown that this structure can accommodate some cationic disorder, with up to 16(2)% sodium on the uranium site, corresponding to the composition α-Na3(U1-x,Nax)O4 (0 < x < 0.18). The α phase adopts a mixed valence state with the presence of U(V) and U(VI). The two polymorphs of this compound described in the literature, m- and β-Na3(U1-x,Nax)O4, have also been investigated, and their relationship to the α phase has been established. The completely disordered low-temperature cubic phase corresponds to a metastable phase. The semiordered high-temperature β phase is cubic, in space group Fd3̅m.

High-energy resolution X-ray spectroscopy at actinide M4,5 and ligand K edges: what we know, what we want to know, and what we can know

“…The actinide M 4,5 HERFD-XANES method gives the opportunity to fingerprint the oxidation state of the actinidecontaining materials. The first U M 4 experiment has been done on the mixed uranium oxides 3 , which was followed by several other Please do not adjust margins Please do not adjust margins studies on the chemical state verification in actinide systems 3,6,9,12,[60][61][62][63][64][65][66][67][68][69][70][71][72][73][74][75][76][77] . Fig.…”

“…The identification of the oxidation states by HERFD has become important for many areas of actinide science since it provides information on how electrons are distributed between elements. The oxidation-reduction (redox) reactions involve the transfer of electrons between chemical species 3,60,63,66,68,69,72,76,77,79 . Many biological processes rely on the electron transfer.…”

Uranium solubility and speciation in reductive soda-lime aluminosilicate glass melts

“…The estimated uncertainty is about 10% for each uranium valence state. A more precise quantitative analysis could be performed using other reference systems, like U4O9 [26,27,30] as a mixed U V /U IV compound or KUO3 [27] as a pure U V reference.…”

“…HR-XANES spectra of the U-doped glasses (AU-Ox, AU-Ar, and AU-C samples) measured at the U M4 edge and compared with the reference spectra of UO2, U3O8 and (UO2)O2(H2O)2.The HR-XANES spectra of the U-doped glasses were collected at the U M4 edge, along with spectra of UO2, U3O8, and metastudtite (UO2)O2(H2O)2 which were used as reference systems. UO2 and (UO2)O2(H2O)2 correspond to pure valence, U IV and U VI respectively, and U3O8 is a mixed-valence uranium oxide containing 33% U VI and 67% U V[26,30]. In Fig.5, the glass absorption spectra recorded are compared with reference spectra.…”

A New Look at the Structural and Magnetic Properties of Potassium Neptunate K2NpO4 Combining XRD, XANES Spectroscopy, and Low-Temperature Heat Capacity

“…4−7 Those studies have revealed intriguing magnetic properties for the α-Na 2 Np VI O 4 7 and Na 4 Np VI O 5 6 compositions and have stressed the need to re-evaluate the Np(VI) crystal-field ground state.…”