Synthesis, crystal structure and lithium ion conductivity of LiMgFSO4
Lithium magnesium fluoride sulfate, LiMgFSO4, has been prepared by reaction of MgSO4·H2O, Li2CO3 and NH4F at 450–500 °C. It crystallizes in space group P of the triclinic system, with Z = 2 and a = 5.1623(7), b = 5.388(1), c = 7.073(1) Å, α = 106.68(1), β = 107.40(1) and γ = 97.50(1)°. The structure is built up from single chains of corner-sharing MgO4F2 octahedra running parallel to the c axis, cross linked via vertex-sharing SO4 tetrahedra, so that each tetrahedron links three different chains. Li resides within the cavities defined by the framework, wherein it is disordered between two half-occupied sites. This structure is isotypic with that of all members of the amblygonite (LiAlFPO4)–montebrasite (LiAlOHPO4) series, and that of tavorite (LiFeOHPO4). It is topologically identical to the titanite (CaTiOSiO4) and kieserite (MgSO4·H2O) structures. The framework structure of LiMgFSO4 facilitates lithium ion conduction [σ (520 °C) = 1.5 × 10-3 S cm−1; Ea = 0.94 eV].