DOE OSTI2020
LiFeSi2O6 crystallizes in the monoclinic P2_1/c space group. The structure is three-dimensional. Li1+ is bonded in a 5-coordinate geometry to five O2- atoms. There are a spread of Li–O bond distances ranging from 2.07–2.42 Å. Fe3+ is bonded to six O2- atoms to form FeO6 octahedra that share corners with six SiO4 tetrahedra and edges with two equivalent FeO6 octahedra. There are a spread of Fe–O bond distances ranging from 1.94–2.18 Å. There are two inequivalent Si4+ sites. In the first Si4+ site, Si4+ is bonded to four O2- atoms to form SiO4 tetrahedra that share corners with three equivalent FeO6 octahedra and corners with two equivalent SiO4 tetrahedra. The corner-sharing octahedra tilt angles range from 32–59°. There is one shorter (1.61 Å) and three longer (1.65 Å) Si–O bond length. In the second Si4+ site, Si4+ is bonded to four O2- atoms to form SiO4 tetrahedra that share corners with three equivalent FeO6 octahedra and corners with two equivalent SiO4 tetrahedra. The corner-sharing octahedra tilt angles range from 40–60°. There are a spread of Si–O bond distances ranging from 1.62–1.66 Å. There are six inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted T-shaped geometry to one Li1+, one Fe3+, and one Si4+ atom. In the second O2- site, O2- is bonded in a distorted trigonal non-coplanar geometry to one Li1+, one Fe3+, and one Si4+ atom. In the third O2- site, O2- is bonded in a bent 150 degrees geometry to two equivalent Si4+ atoms. In the fourth O2- site, O2- is bonded in a 2-coordinate geometry to one Li1+ and two equivalent Si4+ atoms. In the fifth O2- site, O2- is bonded in a 4-coordinate geometry to one Li1+, two equivalent Fe3+, and one Si4+ atom. In the sixth O2- site, O2- is bonded in a 4-coordinate geometry to one Li1+, two equivalent Fe3+, and one Si4+ atom.