Study of the Crystal Structures of Sodium Magnesium and Sodium Nickel Diphosphates

Author： Erragh F. Boukhari A. Abraham F. Elouadi B.

ISSN： 0022-4596

Source： Journal of Solid State Chemistry, Vol.152, Iss.2, 2000-07, pp. : 323-331

Disclaimer: Any content in publications that violate the sovereignty, the constitution or regulations of the PRC is not accepted or approved by CNPIEC.

Previous Menu Next

Abstract

Single-crystal X-ray crystallography studies have shown that diphosphates Na_3.64Mg_2.18(P₂O₇)₂ and Na_3.64Ni_2.18(P₂O₇)₂ crystallize with the same structural type and the same space group P1. Their triclinic lattice parameters are equal to a=10.901 (2), b=9.765 (2), c=6.382 (1) Å, α=112.43 (1)°, β=99.64 (1)°, γ=107.53 (1)°, Z=2 and a=10.889 (5), b=9.705 (4), c=6.358 (4) Å, α=112.46 (4)°, β=99.92 (4)°, γ=107.54 (4)°, Z=2, respectively. The structure could be regarded as a packing of diphosphate groups [P₂O₇]^4- and [MO₆] octahedra (M=Mg, Ni) delimiting cavities and tunnels which host sodium cations. The tunnels are running along [001]. The structure is characterized by mixed (Na, M) sites with an occupation factor ratio equal to ca. 0.82/0.18. Sodium cations are located in five different sites: two cavities (one penta- and the other octa-coordinated) totally occupied and three octahedral interstices, which are partially filled by Na(3), Na(4), and Na(5) according to the respective occupation factors of 0.15, 0.42, and 0.25 for Na_3.64Mg_2.18(P₂O₇)₂ and 0.13, 0.40, and 0.29 in the case of Na_3.64Ni_2.18(P₂O₇)₂.