Materials Data on Ca3AlAs3 by Materials Project

Abstract

Ca3AlAs3 crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. there are three inequivalent Ca2+ sites. In the first Ca2+ site, Ca2+ is bonded to six As3- atoms to form CaAs6 octahedra that share corners with seven equivalent CaAs6 octahedra, corners with three equivalent AlAs4 tetrahedra, corners with three equivalent CaAs5 trigonal bipyramids, edges with four equivalent CaAs6 octahedra, edges with three equivalent AlAs4 tetrahedra, edges with three equivalent CaAs5 trigonal bipyramids, and a faceface with one CaAs6 octahedra. The corner-sharing octahedra tilt angles range from 42–54°. There are a spread of Ca–As bond distances ranging from 2.96–3.43 Å. In the second Ca2+ site, Ca2+ is bonded to five As3- atoms to form distorted CaAs5 trigonal bipyramids that share corners with nine CaAs6 octahedra, corners with two equivalent AlAs4 tetrahedra, edges with four CaAs6 octahedra, edges with two equivalent AlAs4 tetrahedra, edges with two equivalent CaAs5 trigonal bipyramids, and a faceface with one CaAs6 octahedra. The corner-sharing octahedra tilt angles range from 24–58°. There are a spread of Ca–As bond distances ranging from 2.92–3.05 Å. In the third Ca2+ site, Ca2+ is bonded to six As3- atoms to form CaAs6 octahedra that share corners with seven equivalent CaAs6 octahedra, corners with three equivalent AlAs4 tetrahedra, corners with six equivalent CaAs5 trigonal bipyramids, edges with four equivalent CaAs6 octahedra, edges with two equivalent AlAs4 tetrahedra, an edgeedge with one CaAs5 trigonal bipyramid, a faceface with one CaAs6 octahedra, and a faceface with one CaAs5 trigonal bipyramid. The corner-sharing octahedra tilt angles range from 42–54°. There are a spread of Ca–As bond distances ranging from 2.97–3.30 Å. Al3+ is bonded to four As3- atoms to form AlAs4 tetrahedra that share corners with six CaAs6 octahedra, corners with two equivalent AlAs4 tetrahedra, corners with two equivalent CaAs5 trigonal bipyramids, edges with five CaAs6 octahedra, and edges with two equivalent CaAs5 trigonal bipyramids. The corner-sharing octahedra tilt angles range from 21–51°. There are two shorter (2.52 Å) and two longer (2.56 Å) Al–As bond lengths. There are three inequivalent As3- sites. In the first As3- site, As3- is bonded in a 7-coordinate geometry to five Ca2+ and two equivalent Al3+ atoms. In the second As3- site, As3- is bonded in a 7-coordinate geometry to six Ca2+ and one Al3+ atom. In the third As3- site, As3- is bonded to six Ca2+ and one Al3+ atom to form distorted face-sharing AsCa6Al pentagonal bipyramids.