Synthesis,crystal structure and electrical characterization of Cs4[(UO2)2(V2O7)O2], a uranyl divanadate with chains of corner-sharing uranyl square bipyramids |
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| Affiliation: | 1. College of Electrical Engineering and Control Science, Nanjing Tech University, Nanjing, Jiangsu, China.;2. Department of Electronic Engineering, City University of Hong Kong, Hong Kong.;3. College of Automation, Harbin Engineering University, Harbin, Heilongjiang, China.;4. Centre for Vision, Speech and Signal Processing, University of Surrey, Guildford GU2 7XH, U.K.;5. University of Chemistry and Technology, Prague, Czech Republic.;6. School of Electrical and Electronic Engineering, Newcastle University, Newcastle upon Tyne NE1 7RU, U.K.;1. Institut für Informatik, Johannes Gutenberg-Universität Mainz, Mainz 55128, Germany;2. School of Computational Science & Engineering, Georgia Institute of Technology, Atlanta, GA 30332, USA |
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| Abstract: | A new cesium uranyl vanadate Cs4[(UO2)2(V2O7)O2] has been synthesized by solid-state reaction and its structure determined from single-crystal X-ray diffraction data. It crystallizes in the orthorhombic symmetry with space group Pmmn and following cell parameters: a=8.4828(15) Å, b=13.426(2) Å and c=7.1366(13) Å, V=812.8(3) Å3, Z=2 with ρmes=5.39(2) g/cm3 and ρcal=5.38(1) g/cm3. A full-matrix least-squares refinement on the basis of F2 yielded R1=0.027 and wR2=0.066 for 62 parameters with 636 independent reflections with I⩾2σ(I) collected on a BRUKER AXS diffractometer with MoKα radiation and a charge-coupled device detector. The crystal structure is characterized by ∞2[(UO2)2(V2O7)O2]4− corrugated layers parallel to (001). The layers are built up from distorted (UO2)O4 octahedra and divanadate V2O7 units resulting from two VO4 tetrahedra sharing corner. The distorted uranyl octahedra (UO2)O4 are linked by corners to form infinite ∞1[UO5]4− chains parallel to the a-axis. These chains are linked together by symmetrical divanadate units sharing two corners with each chain, the two last corners being oriented towards the same interlayer. The cohesion of the structure is assured by interlayer Cs+ ions. Their mobility within the interlayer space gives rise to a cationic conductivity with an important jump between 635°C and 680°C. Cs4[(UO2)2(V2O7)O2] is readily decomposed by water at 60°C to form the Cs-carnotite analog Cs2(UO2)2(V2O8) compound. |
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