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 23Na 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.

SMITH Anna;  RAISON Philippe;  MARTEL Laura;  PRIEUR Damien;  CHARPENTIER Thibault;  WALLEZ G;  SUARD E.;  SCHEINOST Andreas;  HENNIG Christoph;  MARTIN P.;  KVASHNINA Kristina;  CHEETHAM A.K.;  KONINGS Rudy; 

2015-09-21

AMER CHEMICAL SOC

JRC90135

0020-1669,   

http://pubs.acs.org/doi/abs/10.1021/acs.inorgchem.5b00136,    https://publications.jrc.ec.europa.eu/repository/handle/JRC90135,   

10.1021/acs.inorgchem.5b00136,