Synthesis, crystal structure and ionic conduction of the new alluaudite Na3Bi2(AsO4)3

Abstract Transparent single crystals of alluaudite – type sodium (I) bismuth (III) trisorthoarsenate (V), Na 3 Bi 2 (AsO 4 ) 3 , have been prepared by solid state reaction and have been characterized by X-ray diffraction techniques, infrared spectroscopy and scanning electron microscopy. The title compound crystallizes in the monoclinic space group, C 2/ c , with a = 13.673 (2) A; b = 13.474 (3) A; c = 6.885 (2) A, β = 116.22 (2)°, V = 1137.9 A 3 and Z = 4. The main structural feature is the presence of infinite chains of edge-sharing Bi 2 O 10 dimers, which are linked together by AsO 4 tetrahedra, leading to a three –dimensional open framework enclosing two types of tunnels where Na + cations lodge. The structural model was confirmed by both bond valence sum (BVS) and charge distribution (CHARDI) methods. The conductivity measurements of the compound were carried out from 250 to 500 °C using a frequency response analyzer. The conductivity of the sample at 350 °C is 1.30 × 10 −5  S cm −1 and the activation energy is E a  = 0.85 eV. Compared with other sodium-ion conductors studied previously, the investigated material Na 3 Bi 2 (AsO 4 ) 3 is a medium cation conductor.