Materials Data on CaMgAsO4F by Materials Project

Abstract

CaMgAsO4F crystallizes in the monoclinic Cc 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 2.44–2.73 Å. The Ca–F bond length is 2.27 Å. Mg2+ is bonded to four O2- and two equivalent F1- atoms to form MgO4F2 octahedra that share corners with two equivalent MgO4F2 octahedra and corners with four equivalent AsO4 tetrahedra. The corner-sharing octahedral tilt angles are 45°. There are a spread of Mg–O bond distances ranging from 2.10–2.15 Å. Both Mg–F bond lengths are 1.95 Å. As5+ is bonded to four O2- atoms to form AsO4 tetrahedra that share corners with four equivalent MgO4F2 octahedra. The corner-sharing octahedra tilt angles range from 44–56°. There is two shorter (1.72 Å) and two longer (1.73 Å) As–O bond length. There are four inequivalent O2- sites. In the first O2- site, O2- is bonded in a 3-coordinate geometry to one Ca2+, one Mg2+, and one As5+ atom. In the second O2- site, O2- is bonded in a 4-coordinate geometry to two equivalent Ca2+, one Mg2+, and one As5+ atom. In the third O2- site, O2- is bonded in a 4-coordinate geometry to two equivalent Ca2+, one Mg2+, and one As5+ atom. In the fourth O2- site, O2- is bonded in a 3-coordinate geometry to one Ca2+, one Mg2+, and one As5+ atom. F1- is bonded in a distorted trigonal planar geometry to one Ca2+ and two equivalent Mg2+ atoms.