Synthesis, crystal structure, electrical properties, and sodium transport pathways of the new arsenate Na4Co7(AsO4)6

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) angstrom, b = 14.7837(9) angstrom, c = 6.6845(7) angstrom, and beta = 105.545(9)degrees. 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 Nal-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 degrees C to 560 degrees C using the complex impedance spectroscopy over the range of 13 MHz-5 Hz. The ionic bulk conductivity value of the sample at 360 degrees 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. (C) 2016 Elsevier Inc. All rights reserved.