Materials Data on Ca2Al2Si(HO4)2 by Materials Project

Abstract

Ca2Al2Si(HO4)2 crystallizes in the tetragonal I-42m space group. The structure is three-dimensional. Ca2+ is bonded to six O2- atoms to form CaO6 octahedra that share corners with two equivalent SiO4 tetrahedra, corners with four equivalent AlO4 tetrahedra, and edges with three equivalent CaO6 octahedra. There are a spread of Ca–O bond distances ranging from 2.31–2.53 Å. Al3+ is bonded to four O2- atoms to form AlO4 tetrahedra that share corners with four equivalent CaO6 octahedra, corners with two equivalent AlO4 tetrahedra, and corners with two equivalent SiO4 tetrahedra. The corner-sharing octahedra tilt angles range from 67–69°. There is two shorter (1.76 Å) and two longer (1.79 Å) Al–O bond length. Si4+ is bonded to four equivalent O2- atoms to form SiO4 tetrahedra that share corners with four equivalent CaO6 octahedra and corners with four equivalent AlO4 tetrahedra. The corner-sharing octahedral tilt angles are 64°. All Si–O bond lengths are 1.65 Å. H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.97 Å. There are three inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted single-bond geometry to three equivalent Ca2+ and one H1+ atom. In the second O2- site, O2- is bonded in a distorted trigonal planar geometry to one Ca2+ and two equivalent Al3+ atoms. In the third O2- site, O2- is bonded in a distorted trigonal planar geometry to one Ca2+, one Al3+, and one Si4+ atom.