Materials Data on CaFe3Si2O9 by Materials Project
CaFe3Si2O9 crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. Ca2+ is bonded in a 7-coordinate geometry to seven O2- atoms. There are a spread of Ca–O bond distances ranging from 2.27–2.53 Å. There are two inequivalent Fe+2.67+ sites. In the first Fe+2.67+ site, Fe+2.67+ is bonded to six O2- atoms to form FeO6 octahedra that share corners with two equivalent FeO6 octahedra, corners with three SiO4 tetrahedra, and edges with five FeO6 octahedra. The corner-sharing octahedral tilt angles are 15°. There are a spread of Fe–O bond distances ranging from 1.88–2.24 Å. In the second Fe+2.67+ site, Fe+2.67+ is bonded to six O2- atoms to form distorted FeO6 octahedra that share corners with five SiO4 tetrahedra and edges with four equivalent FeO6 octahedra. There are a spread of Fe–O bond distances ranging from 1.93–2.30 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 five FeO6 octahedra and a cornercorner with one SiO4 tetrahedra. The corner-sharing octahedra tilt angles range from 39–63°. There are a spread of Si–O bond distances ranging from 1.59–1.67 Å. In the second Si4+ site, Si4+ is bonded to four O2- atoms to form SiO4 tetrahedra that share corners with six FeO6 octahedra and a cornercorner with one SiO4 tetrahedra. The corner-sharing octahedra tilt angles range from 49–65°. There are a spread of Si–O bond distances ranging from 1.65–1.68 Å. There are seven inequivalent O2- sites. In the first O2- site, O2- is bonded in a 4-coordinate geometry to one Ca2+, two equivalent Fe+2.67+, and one Si4+ atom. In the second O2- site, O2- is bonded in a 4-coordinate geometry to one Ca2+, two Fe+2.67+, and one Si4+ atom. In the third O2- site, O2- is bonded in a distorted trigonal planar geometry to one Ca2+ and two Si4+ atoms. In the fourth O2- site, O2- is bonded in a bent 150 degrees geometry to one Fe+2.67+ and one Si4+ atom. In the fifth O2- site, O2- is bonded to five Fe+2.67+ atoms to form edge-sharing OFe5 square pyramids. In the sixth O2- site, O2- is bonded in a distorted trigonal non-coplanar geometry to one Ca2+ and two equivalent Fe+2.67+ atoms. In the seventh O2- site, O2- is bonded in a distorted rectangular see-saw-like geometry to one Ca2+, two Fe+2.67+, and one Si4+ atom.