Synthesis, structural and electrical properties of a new cobalt arsenate NaCo sub(2)As sub(3)O sub(10)

The title compound sodium dicobalt triarsenate NaCo sub(2)As sub(3)O sub(10) has been synthesized by solid state reaction. Crystal structure and electrical properties were studied by X-ray diffraction and complex impedance spectroscopy, respectively. The obtained structural model is supported by charge-distribution (CHARDI) analysis and bond-valence-sum (BVS) validations tools. The structure (triclinic, P-1, a=6.800 (8) Aa, b=7.816 (9) Aa, c=8.718 (3) Aa, alpha =108.03 (2) degree , beta =108.48 (3) degree , gamma =100.11 (2) degree ) can be described as a three-dimensional framework resulted from corner-connection between cobalt metallic chains running along [-110] and As sub(3)O sub(10) groups; the negative charge is balanced by Na super(+) ions which house the two tunnels parallel to a and b axes. Ball milling was used as mechanical means to reduce the particles sizes of the synthesized powder. At the optimal sintering temperature of 650 degree C, 85% of the relative density was obtained. The conductivity measurements show that NaCo sub(2)As sub(3)O sub(10) is a cationic conductor with an activation energy of 0.48 eV and a conductivity of sigma =1.210 super(-5) S cm super(-1) at 310 degree C. The BVS model is extended to simulate the ionic migration pathways of alkali cations in the anionic framework. 1D pathways link Na atoms along the a-axis with bond valence mismatch | Delta V(Na)|=0.64 v.u.