Browsing by Author "Marzouki, R"

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    Synthesis, crystal structure, electrical properties, and sodium transport pathways of the new arsenate Na4Co7(AsO4)6
    (Elsevier, 2016-07-01) Ben Smida, Y; Marzouki, R; Georges, S; Kutteh, R; Avdeev, M; Guesmi, A; Zid, MF
    A new sodium cobalt (II) arsenate Na4Co7(AsO4)6 has been synthesized by a solid-state reaction and its crystal structure determined from single crystal X-ray diffraction data. It crystallizes in the monoclinic system, space group C2/m, with a=10.7098(9) Å, b=14.7837(9) Å, c=6.6845(7) Å, and β=105.545(9)°. The structure is described as a three-dimensional framework built up of corner-edge sharing CoO6, CoO4 and AsO4 polyhedra, with interconnecting channels along [100] in which the Na+ cations are located. The densest ceramics with relative density of 94% was obtained by ball milling and optimization of sintering temperature, and its microstructure characterized by scanning electron microscopy. The electrical properties of the ceramics were studied over a temperature interval from 280 °C to 560 °C using the complex impedance spectroscopy over the range of 13 MHz–5 Hz. The ionic bulk conductivity value of the sample at 360 °C is 2.51 10−5 S cm−1 and the measured activation energy is Ea=1 eV. The sodium migration pathways in the crystal structure were investigated computationally using the bond valence site energy (BVSE) model and classical molecular dynamics (MD) simulations. © 2016 Elsevier Inc.
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    Synthesis, electrical properties and Na+ migration pathways of Na2CuP1.5As0.5O7
    (MDPI, 2020-03-06) ALQarni, OSA; Marzouki, R; Ben Smida, Y; Alghamdi, MM; Avdeev, M; Belhadj Tahar, R; Zid, MF
    A new member of sodium metal diphosphate-diarsenate, Na2CuP1.5As0.5O7, was synthesized as polycrystalline powder by a solid-state route. X-ray diffraction followed by Rietveld refinement show that the studied material, isostructural with β-Na2CuP2O7, crystallizes in the monoclinic system of the C2/c space group with the unit cell parameters a = 14.798(2) Å; b = 5.729(3) Å; c = 8.075(2) Å; β = 115.00(3)°. The structure of the studied material is formed by Cu2P4O15 groups connected via oxygen atoms that results in infinite chains, wavy saw-toothed along the [001] direction, with Na+ ions located in the inter-chain space. Thermal study using DSC analysis shows that the studied material is stable up to the melting point at 688 °C. The electrical investigation, using impedance spectroscopy in the 260–380 °C temperature range, shows that the Na2CuP1.5As0.5O7 compound is a fast-ion conductor with σ350 °C = 2.28 10−5 Scm−1 and Ea = 0.6 eV. Na+ ions pathways simulation using bond-valence site energy (BVSE) supports the fast three-dimensional mobility of the sodium cations in the inter-chain space. © MDPI
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    Synthesis, structure and Na+ migration pathways of new Wylleite-type Na1.25Co2.187Al1.125(AsO4)3
    (IOP Publishing, 2019-12-04) Marzouki, R; Ben Smida, Y; Avdeev, M; Alghamdi, MM; Zid, MF
    A new sodium cobalt (II) aluminum arsenate Na1.25Co2.187Al1.125(AsO4)3 has been synthesized by solid state reaction method and its structure has been determined by single crystal X-ray diffraction at room temperature. The title material crystallizes in the monoclinic system, space group P21/c with the unit cell parameters: a = 6.532(2) Å, b = 12.492(2) Å, c = 11.060(2) Å, β = 99.44 (2)°, V = 890.3(3) Å3 and Z = 4. The peculiarity of this structure is the Al3+ and Co2+ distribution over four crystallographic independent sites. Charge distribution (CHARDI) calculations and bond-valence sum (BVS) analysis were used to support the proposed structural model. The crystal structure of the title compound features a 3D anionic framework built of corner-edge sharing (Al3+/Co2+)O6 and AsO4 polyhedra, with interconnecting channels where the Na+ cations are located. The title compound is a new member of Wylleite family with an additional new Na+ site denoted X(3). The modelling of pathways transport of Na+ in the anionic framework shows that only the sodium Na1 can diffuse through an infinite 1D pathway along [100] direction. The empirical activation energy deduced from the Bond-Valence Site Energy (BVSE) model is about 5.45 eV. © 2019 IOP Publishing Ltd
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    Synthesis, structure, electrical properties and Na+ migration pathways of Na2CoP1.5As0.5O7
    (Elsevier, 2020-05-01) Marzouki, R; Ben Smida, Y; Sonni, M; Avdeev, M; Zid, MF
    Sodium cobalt di(phosphate/arsenate) Na2CoP1.5As0.5O7 has been synthesized as polycrystalline powder and single crystals by solid state reaction. The structure has been determined by X-ray diffraction at room temperature. The title material crystallizes in the tetragonal system, space group P42/mnm with the unit cell parameters: a = 7.764(3) Å, c = 10.385(3) Å, V = 626.0(4) Å3 and Z = 4. The two tools of crystal structure validation, Bond Valence Sum (BVS) and Charge distribution (CHARDI) methods, have confirmed the crystal structure model. The anionic framework is built of layers of corner sharing (P/As)O4 and CoO6 polyhedra. The sodium atoms are located in the interlayer space. Quantitative analysis using ICP-MS is used to confirm the elemental composition of the polycrystalline powder. Thermal analyzes show a phase transition at 675 °C before the melting point of 700 °C. The electrical properties of the title compound have been characterized by impedance spectroscopy in the 240°C–360 °C temperature range. At 240 °C, the conductivity value of the sample with relative density of 85% is 4 10−6 Scm−1 and the activation energy was Ea = 0.56 eV. The calculated conductivity corrected for porosity is σd (240°C) = 1.88 10−5 Scm−1. The Na+ transport pathways in the interlayer space was simulated using the Band Valence Site Energy (BVSE) model. The BVSE model was also used to explain the effect of the P/As substitution on the electrical properties of the title compound. © 2019 Elsevier Inc.