Crystal structure and ionic conductivity of the new cobalt polyphosphate NaCo(PO3)3

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Polycrystalline sample of sodium cobalt triphosphate NaCo(PO3)3 was obtained by solid-state reaction and characterized by X-ray powder diffraction. The title compound is isostructural to NaZn(PO3)3 and its structure was refined by the Rietveld refinement in the cubic system, space group Pa̅, with a=14.2484(4) Å. The obtained structural model is supported by bond valence sum (BVS) and charge distribution (CD) methods. The structure is described as a three-dimensional open-anionic framework built up of corner-sharing CoO6 and PO4 polyhedra with interconnecting channels along the 3-axis, in which the Na+ cations are located. The ionic conductivity measurements are performed on pellets with relative density of 84%. The electrical conductivity is 1.01×10−5 S cm−1 at 480 °C and the activation energy deduced from the slope is 1.1 eV. The correlation between crystal structure and ionic conductivity was studied by the means of the bond-valence-site-energy (BVSE) model. The main result is that sodium transport is made mainly via Na2 and Na3 sites. © 2015 Elsevier Inc.
X-ray diffraction, Ionic conductivity, Crystal structure, Valence, Polycrystals, Phosphates
Ben Smida, Y., Guesmi, A., Georges, S., Avdeev, M., & Zid, M. F. (2016). Crystal structure and ionic conductivity of the new cobalt polyphosphate NaCo(PO3)3. Journal of Solid State Chemistry, 234, 15-21. doi:10.1016/j.jssc.2015.11.029