DOE OSTI2020
Li2FeO2F is Molybdenum Carbide MAX Phase-derived structured and crystallizes in the monoclinic C2 space group. The structure is three-dimensional. there are five inequivalent Li1+ sites. In the first Li1+ site, Li1+ is bonded to four O2- and two F1- atoms to form LiO4F2 octahedra that share corners with two LiO2F4 octahedra, corners with four FeO6 octahedra, edges with four FeO6 octahedra, and edges with eight LiO4F2 octahedra. The corner-sharing octahedra tilt angles range from 2–10°. There are a spread of Li–O bond distances ranging from 2.03–2.25 Å. There are one shorter (2.13 Å) and one longer (2.16 Å) Li–F bond lengths. In the second Li1+ site, Li1+ is bonded to four O2- and two F1- atoms to form LiO4F2 octahedra that share corners with two LiO2F4 octahedra, corners with four FeO6 octahedra, edges with four FeO6 octahedra, and edges with eight LiO4F2 octahedra. The corner-sharing octahedra tilt angles range from 1–7°. There are a spread of Li–O bond distances ranging from 2.07–2.20 Å. There are one shorter (2.19 Å) and one longer (2.22 Å) Li–F bond lengths. In the third Li1+ site, Li1+ is bonded to two equivalent O2- and four F1- atoms to form LiO2F4 octahedra that share corners with six LiO4F2 octahedra, edges with three equivalent FeO2F4 octahedra, and edges with nine LiO4F2 octahedra. The corner-sharing octahedra tilt angles range from 1–9°. Both Li–O bond lengths are 2.06 Å. There are two shorter (2.12 Å) and two longer (2.13 Å) Li–F bond lengths. In the fourth Li1+ site, Li1+ is bonded to four O2- and two F1- atoms to form LiO4F2 octahedra that share corners with two LiO2F4 octahedra, corners with four FeO6 octahedra, edges with four FeO6 octahedra, and edges with eight LiO4F2 octahedra. The corner-sharing octahedra tilt angles range from 3–9°. There are a spread of Li–O bond distances ranging from 2.03–2.30 Å. Both Li–F bond lengths are 2.12 Å. In the fifth Li1+ site, Li1+ is bonded to two equivalent O2- and four F1- atoms to form LiO2F4 octahedra that share corners with six LiO4F2 octahedra, edges with three equivalent FeO2F4 octahedra, and edges with nine LiO4F2 octahedra. The corner-sharing octahedra tilt angles range from 2–7°. Both Li–O bond lengths are 2.10 Å. There are two shorter (2.05 Å) and two longer (2.17 Å) Li–F bond lengths. There are four inequivalent Fe3+ sites. In the first Fe3+ site, Fe3+ is bonded to six O2- atoms to form FeO6 octahedra that share corners with six LiO4F2 octahedra, edges with six LiO4F2 octahedra, and edges with six FeO6 octahedra. The corner-sharing octahedra tilt angles range from 3–4°. There are two shorter (2.05 Å) and four longer (2.06 Å) Fe–O bond lengths. In the second Fe3+ site, Fe3+ is bonded to two equivalent O2- and four F1- atoms to form FeO2F4 octahedra that share corners with six LiO4F2 octahedra and edges with twelve LiO4F2 octahedra. The corner-sharing octahedra tilt angles range from 5–10°. Both Fe–O bond lengths are 1.86 Å. There are two shorter (2.08 Å) and two longer (2.19 Å) Fe–F bond lengths. In the third Fe3+ site, Fe3+ is bonded to six O2- atoms to form FeO6 octahedra that share corners with six LiO4F2 octahedra, edges with six LiO4F2 octahedra, and edges with six FeO6 octahedra. The corner-sharing octahedra tilt angles range from 5–7°. There are four shorter (2.05 Å) and two longer (2.06 Å) Fe–O bond lengths. In the fourth Fe3+ site, Fe3+ is bonded to six O2- atoms to form FeO6 octahedra that share corners with six LiO4F2 octahedra, edges with six LiO4F2 octahedra, and edges with six FeO6 octahedra. The corner-sharing octahedra tilt angles range from 5–7°. There are two shorter (2.05 Å) and four longer (2.06 Å) Fe–O bond lengths. There are four inequivalent O2- sites. In the first O2- site, O2- is bonded to three Li1+ and three Fe3+ atoms to form OLi3Fe3 octahedra that share corners with two FLi5Fe octahedra, corners with four OLi3Fe3 octahedra, edges with two FLi5Fe octahedra, and edges with ten OLi3Fe3 octahedra. The corner-sharing octahedra tilt angles range from 0–6°. In the second O2- site, O2- is bonded to five Li1+ and one Fe3+ atom to form OLi5Fe octahedra that share corners with two FLi5Fe octahedra, corners with four OLi3Fe3 octahedra, edges with four OLi3Fe3 octahedra, and edges with eight FLi5Fe octahedra. The corner-sharing octahedra tilt angles range from 1–10°. In the third O2- site, O2- is bonded to three Li1+ and three Fe3+ atoms to form OLi3Fe3 octahedra that share corners with two FLi5Fe octahedra, corners with four OLi3Fe3 octahedra, edges with two FLi5Fe octahedra, and edges with ten OLi3Fe3 octahedra. The corner-sharing octahedra tilt angles range from 0–9°. In the fourth O2- site, O2- is bonded to three Li1+ and three Fe3+ atoms to form OLi3Fe3 octahedra that share corners with two FLi5Fe octahedra, corners with four OLi3Fe3 octahedra, edges with two FLi5Fe octahedra, and edges with ten OLi3Fe3 octahedra. The corner-sharing octahedra tilt angles range from 0–8°. There are two inequivalent F1- sites. In the first F1- site, F1- is bonded to five Li1+ and one Fe3+ atom to form FLi5Fe octahedra that share corners with two FLi5Fe octahedra, corners with four OLi3Fe3 octahedra, edges with five FLi5Fe octahedra, and edges with seven OLi3Fe3 octahedra. The corner-sharing octahedra tilt angles range from 1–15°. In the second F1- site, F1- is bonded to five Li1+ and one Fe3+ atom to form FLi5Fe octahedra that share corners with two FLi5Fe octahedra, corners with four OLi3Fe3 octahedra, edges with five FLi5Fe octahedra, and edges with seven OLi3Fe3 octahedra. The corner-sharing octahedra tilt angles range from 1–10°.