An arsenate with the alpha-CrPO4 structure type, NaCa1-xNi3-2xAl2x(AsO4)(3) (x=0.23): crystal structure, charge-distribution and bond-valencesum analyses

作者：Ben Smail Ridha; Zid Mohamed Faouzi

来源：Acta Crystallographica Section C-Structural Chemistry, 2017, 73(11): 896-+.

DOI：10.1107/S2053229617013213

<jats:p>Since the discovery of electrochemically active LiFePO<jats:sub>4</jats:sub>, materials with tunnel and layered structures built up of transition metals and polyanions have become the subject of much research. A new quaternary arsenate, sodium calcium trinickel aluminium triarsenate, NaCa<jats:sub>1–<jats:italic>x</jats:italic>
</jats:sub>Ni<jats:sub>3–2<jats:italic>x</jats:italic>
</jats:sub>Al<jats:sub>2<jats:italic>x</jats:italic>
</jats:sub>(AsO<jats:sub>4</jats:sub>)<jats:sub>3</jats:sub> (<jats:italic>x</jats:italic> = 0.23), was synthesized using the flux method in air at 1023 K and its crystal structure was determined from single-crystal X-ray diffraction (XRD) data. This material was also characterized by qualitative energy-dispersive X-ray spectroscopy (EDS) analysis and IR spectroscopy. The crystal structure belongs to the α-CrPO<jats:sub>4</jats:sub> type with the space group <jats:italic>Imma</jats:italic>. The structure is described as a three-dimensional framework built up of corner-edge-sharing NiO<jats:sub>6</jats:sub>, (Ni,Al)O<jats:sub>6</jats:sub> and AsO<jats:sub>4</jats:sub> polyhedra, with channels running along the [100] and [010] directions, in which the sodium and calcium cations are located. The proposed structural model has been validated by bond-valence-sum (BVS) and charge-distribution (CHARDI) tools. The sodium ionic conduction pathways in the anionic framework were investigated by means of the bond-valence site energy (BVSE) model, which predicted that the studied material will probably be a very poor Na<jats:sup>+</jats:sup> ion conductor (bond-valence activation energy ∼7 eV).</jats:p>

• 出版日期2017-11