Materials Data on CaAlSiO4F by Materials Project
CaAlFSiO4 crystallizes in the monoclinic C2/c space group. The structure is three-dimensional. Ca2+ is bonded in a 7-coordinate geometry to six O2- and one F1- atom. There are a spread of Ca–O bond distances ranging from 2.35–2.60 Å. The Ca–F bond length is 2.30 Å. Al3+ is bonded to four O2- and two equivalent F1- atoms to form AlO4F2 octahedra that share corners with two equivalent AlO4F2 octahedra and corners with four equivalent SiO4 tetrahedra. The corner-sharing octahedral tilt angles are 37°. There is two shorter (1.89 Å) and two longer (1.93 Å) Al–O bond length. Both Al–F bond lengths are 1.85 Å. Si4+ is bonded to four O2- atoms to form SiO4 tetrahedra that share corners with four equivalent AlO4F2 octahedra. The corner-sharing octahedra tilt angles range from 35–52°. There is two shorter (1.65 Å) and two longer (1.66 Å) Si–O bond length. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded in a 4-coordinate geometry to two equivalent Ca2+, one Al3+, and one Si4+ atom. In the second O2- site, O2- is bonded in a 3-coordinate geometry to one Ca2+, one Al3+, and one Si4+ atom. F1- is bonded in a 3-coordinate geometry to one Ca2+ and two equivalent Al3+ atoms.