The influence of P/As substitution in the melilite‐like Na2Co(P2–xAsx)O7 (x = 0.40 and 0.93) solid solutions

• Published in: Acta crystallographica. Section C, Crystal structure communications Crystal structure communications, 2017-04, Vol.73 (4), p.331-336
• Main Authors: Issaoui, Chokri, Chebbi, Hammouda, Guesmi, Abderrahmen
• Format: Article
• Language: English
• Subjects: Arsenic; bidimensional conduction pathways; bond valence sum (BVS); Cations; charge distribution (CHARDI); Cobalt; Crystal structure; Electric properties; Electrical properties; Na2Co(P,As)2O7; P/As substitution; Slabs; Sodium; sodium conduction properties; Solid solutions; Structural models
• ISSN: 2053-2296; 0108-2701; 2053-2296; 1600-5759
• DOI: 10.1107/S2053229617003771

To investigate the influence of P/As substitution on structures and electrical properties, e.g. the effect on material densities, two new solid P/As‐doped solutions, Na2CoP1.60As0.40O7 (disodium cobalt diphosphorus arsenic heptaoxide) and Na2CoP1.07As0.93O7 (disodium cobalt phosphorus arsenic heptaoxide), with melilite‐like structures have been synthesized by solid‐state reactions. Their unit‐cell parameters are in agreement with Vegard's law. The obtained structural models were investigated by the bond valence sum (BVS) and charge distribution (CHARDI) validation tools and, for the latter, the structures are described as being built on anion‐centred polyhedra. The frameworks can be described as layered and formed by {[Co(P,As)2O7]2−}∞ slabs, with alkali cations sandwiched between the layers and with the interlayer spaces increased due to P/As substitution. The BVS model was extended to a preliminary simulation of the sodium conduction properties in the studied structural type and suggests that the most probable sodium conduction pathways are bidimensional, at the (002) planes. Crystal structures of the solid solutions Na2CoP1.60As0.40O7 and Na2CoP1.07As0.93O7 have been determined and investigated by BVS (bond valence sum) and CHARDI (charge distribution) validation tools. The BVS model also allowed simulation of the sodium conduction pathways in the studied structural type.