A new uranyl niobate sheet in the cesium uranyl niobate Cs{sub 9}[(UO{sub 2}){sub 8}O{sub 4}(NbO{sub 5})(Nb{sub 2}O{sub 8}){sub 2}]
- UCCS-Equipe de Chimie du Solide, UMR CNRS 8181, USTL-ENSCL, B.P. 90108, 59652 Villeneuve d'Ascq Cedex (France)
A new cesium uranyl niobate, Cs{sub 9}[(UO{sub 2}){sub 8}O{sub 4}(NbO{sub 5})(Nb{sub 2}O{sub 8}){sub 2}] or Cs{sub 9}U{sub 8}Nb{sub 5}O{sub 41} has been synthesized by high-temperature solid-state reaction, using a mixture of U{sub 3}O{sub 8}, Cs{sub 2}CO{sub 3} and Nb{sub 2}O{sub 5}. Single crystals were obtained by incongruent melting of a starting mixture with metallic ratio=Cs/U/Nb=1/1/1. The crystal structure of the title compound was determined from single crystal X-ray diffraction data, and solved in the monoclinic system with the following crystallographic data: a=16.729(2) A, b=14.933(2) A, c=20.155(2) A{beta}=110.59(1){sup o}, P2{sub 1}/c space group and Z=4. The crystal structure was refined to agreement factors R{sub 1}=0.049 and wR{sub 2}=0.089, calculated for 4660 unique observed reflections with I{>=}2{sigma}(I), collected on a BRUKER AXS diffractometer with MoK{alpha} radiation and a CCD detector. In this structure the UO{sub 7} uranyl pentagonal bipyramids are connected by sharing edges and corners to form a uranyl layer {sub {infinity}}{sup 2}[U{sub 8}O{sub 36}] corresponding to a new anion-sheet topology, and creating triangular, rectangular and square vacant sites. The two last sites are occupied by Nb{sub 2}O{sub 8} entities and NbO{sub 5} square pyramids, respectively, to form infinite uranyl niobate sheets {sub {infinity}}{sup 2}[(UO{sub 2}){sub 8}O{sub 4}(NbO{sub 5})(Nb{sub 2}O{sub 8}){sub 2}]{sup 9-} stacking along the [010] direction. The Nb{sub 2}O{sub 8} entities result from two edge-shared NbO{sub 5} square pyramids. The Cs{sup +} cations are localized between layers and ensured the cohesion of the structure. The cesium cation mobility between the uranyl niobate sheets was studied by electrical measurements. The conductivity obeys the Arrhenius law in all the studied temperature domains. The observed low conductivity values with high activation energy may be explained by the strong connection of the Cs{sup +} cations to the infinite uranyl niobate layers and by the high density of these cations in the interlayer space without vacant site. Infrared spectroscopy investigated at room temperature in the frequency range 400-4000 cm{sup -1}, showed some characteristic bands of uranyl ion and niobium polyhedra. - Graphical abstract: View of the {sub {infinity}}{sup 2}[U{sub 8}O{sub 36}] uranyl infinite layer formed by association of [U{sub 6}O{sub 30}] and [U{sub 2}O{sub 12}] uranyl blocks in Cs{sub 9}[(UO{sub 2}){sub 8}O{sub 4}(NbO{sub 5})(Nb{sub 2}O{sub 8}){sub 2}].
- OSTI ID:
- 21128242
- Journal Information:
- Journal of Solid State Chemistry, Vol. 181, Issue 4; Other Information: DOI: 10.1016/j.jssc.2008.01.015; PII: S0022-4596(08)00009-1; Copyright (c) 2008 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved; Country of input: International Atomic Energy Agency (IAEA); ISSN 0022-4596
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
ABSORPTION SPECTROSCOPY
ACTIVATION ENERGY
CESIUM COMPOUNDS
CESIUM IONS
CHARGE-COUPLED DEVICES
CRYSTALLOGRAPHY
INFRARED SPECTRA
LAYERS
MONOCLINIC LATTICES
MONOCRYSTALS
NIOBATES
NIOBIUM OXIDES
SPACE GROUPS
SYNTHESIS
TEMPERATURE RANGE 0273-0400 K
URANYL COMPOUNDS
X-RAY DIFFRACTION