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- Title
Revision of the symmetry and the crystal structure of cejkaite, Na<sub>4</sub>(UO<sub>2</sub>)(CO<sub>3</sub>)<sub>3</sub>.
- Authors
PLÁŠIL, JAKUB; FEJFAROVÁ, KARLA; DUŠEK, MICHAL; ŠKODA, RADEK; ROHLÍČEK, JAN
- Abstract
The crystal structure of čejkaite, Na4(UO2)(CO3)3, from the type locality, was determined for the first time by single-crystal X-ray diffraction. In contrast to the previously reported pseudohexagonal triclinic symmetry, the current data indicate čejkaite is monoclinic, triply twinned, and belongs to the space group Cc. Refined unit-cell parameters are a = 9.2919(8), b = 16.0991(11), c = 6.4436(3) Å, b = 91.404(5)°, and V = 963.62(12) Å3. The monoclinic unit cell is also supported by the good fit to the powder diffraction data. The structure of čejkaite consists of uranyl tricarbonate clusters, forming sheets sub-parallel to (001) by sharing edges with (NaΦ) polyhedra. Sheets are interconnected through the uranyl O atoms and columns of (Na1Φ) polyhedra that share their trigonal faces. All Na atoms in the structure are in sixfold coordination . The structure refinement yielded Robs = 0.0424 for 1687 observed reflections [Iobs > 3σ(I)] and 0.0538 for all 2016 unique reflections. Refinement and bond-valence analysis of the structure confirmed the previously proposed formula Na4(UO2)(CO3)3, Z = 4.
- Subjects
SYMMETRY; CRYSTAL structure; SODIUM compounds; ALKALI metal compounds; URANIUM compounds
- Publication
American Mineralogist, 2013, Vol 98, Issue 4, p549
- ISSN
0003-004X
- Publication type
Article
- DOI
10.2138/am.2013.4331