Structural studies of the rhombohedral and orthorhombic monouranates: CaUO4, alpha-SrUO4, beta-SrUO4 and BaUO4

作者：Murphy Gabriel; Kennedy Brendan J^*; Johannessen Bernt; Kimpton Justin A; Avdeev Maxim; Griffith Christopher S; Thorogood Gordon J; Zhang Zhaoming

来源：Journal of Solid State Chemistry, 2016, 237: 86-92.

DOI：10.1016/j.jssc.2016.01.019

• Uranium oxide
• Neutron diffraction
• Anion vacancies
• Crystal structure

The structures of some AUO(4) (A=Ca, Sr, or Ba) oxides have been determined using a combination of neutron and synchrotron X-ray diffraction, supported by X-ray absorption spectroscopic measurements at the U L-3-edge. The smaller Ca cation favours a rhombohedral AUO(4) structure with 8-coordinate UO8 moieties whilst an orthorhombic structure based on UO6 groups is found for BaUO4. Both the rhombohedral and orthorhombic structures can be stabilised for SrUO4. The structural studies suggest that the bonding requirements of the A site cation play a significant role in determining which structure is favoured. In the rhombohedral structure, Bond Valence Sums demonstrate the A site is invariably over bonded, which, in the case of rhombohedral alpha-SrUO4, is compensated for by the formation of vacancies in the oxygen sub-lattice. The uranium cation, with its flexible oxidation state, is able to accommodate this by inducing vacancies along its equatorial coordination site as demonstrated by neutron powder diffraction.

• 出版日期2016-5