Abstract
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 Pa (3) over bar, with a = 14.2484 (4) angstrom. 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 x 10(-5) S cm(-1) at 480 degrees 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. (C) 2015 Elsevier Inc. All rights reserved.