Crystal structures of the new fluorophosphates Li9Mg 3[PO4]4F3 and Li 2Mg[PO4]F and ionic conductivities of selected compositions

Hamdi Yahia, Masahiro Shikano, Tomonari Takeuchi, Hironori Kobayashi, Mitsuru Itoh

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Abstract

The new compounds Li2Mg[PO4]F and Li 9Mg3[PO4]4F3 have been synthesized by a solid state reaction route. The crystal structures were determined from single-crystal X-ray diffraction data. Li2Mg[PO 4]F crystallizes with the orthorhombic Li2Ni[PO 4]F structure, space group Pnma, a = 10.7874(3), b = 6.2196(5), c = 11.1780(4) Å, V = 721.13(10) Å3, and Z = 8, whereas Li9Mg3[PO4]4F3 crystallizes with hexagonal symmetry, space group P63, with a = 12.6159(6), c = 5.0082(4) Å, V = 690.32(7) Å3, and Z = 2. A merohedral twinning was taken into account for its structural refinement. The structure of Li2Mg[PO4]F contains MgO3F chains made up of edge-sharing MgO4F2 octahedra. These chains are interlinked by PO4 tetrahedra forming a 3D-Mg[PO4]F framework. The lithium atoms occupy mainly three distinct crystallographic sites. The structure of Li9Mg3[PO4] 4F3 consists of corner-sharing MgO4F 2 octahedra forming MgO4F chains running along the c axis. These chains are interlinked by PO4 tetrahedra forming a 3D-Mg 3[PO4]4F3 framework with hexagonal and pentagonal tunnels, in which are located the Li atoms. This study reveals also a strong relationship between Li2Mg[PO4]F-, Mg 1-xFexAl3[BO3][SiO 4]O2- and P21/c-Li5V[PO 4]2F2- structures; and between P6 3-Li9Mg3[PO4]4F 3 and P21/c-Na2Mn[PO4]F. The ionic conductivities σ of the composite material Li6Mg 4[PO4]3[SO4]F3 and Li9Mg3[PO4]4F3, estimated using electrochemical impedance spectroscopic analyses at 300 °C, are 3.9 × 10-5 and 10-4 S cm-1 with activation energies of 0.524 eV and 0.835 eV, respectively.

Original languageEnglish
Pages (from-to)5858-5869
Number of pages12
JournalJournal of Materials Chemistry A
Volume2
Issue number16
DOIs
Publication statusPublished - 28 Apr 2014
Externally publishedYes

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ASJC Scopus subject areas

  • Chemistry(all)
  • Renewable Energy, Sustainability and the Environment
  • Materials Science(all)

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