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 450-500degreesC. It crystallizes in space group P (1) over bar of the triclinic system, with Z = 2 and a = 5.1623(7), b = 5.388(1), c = 7.073(1) Angstrom, alpha = 106.68(1), beta = 107.40(1) and gamma = 97.50(1)degrees. 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 [sigma (520degreesC) = 1.5 x 10(-3) S cm(-1); E-a = 0.94 eV].