Materials Data on CaAlCuSi2O9 by Materials Project
CaCuAlSi2O9 crystallizes in the monoclinic C2/m space group. The structure is three-dimensional. Ca is bonded in a 8-coordinate geometry to eight O atoms. There are a spread of Ca–O bond distances ranging from 2.31–2.95 Å. Cu is bonded to five O atoms to form distorted CuO5 trigonal bipyramids that share corners with two equivalent SiO4 tetrahedra and edges with two equivalent AlO6 octahedra. There are a spread of Cu–O bond distances ranging from 1.85–2.10 Å. Al is bonded to six O atoms to form AlO6 octahedra that share corners with four equivalent SiO4 tetrahedra and edges with two equivalent CuO5 trigonal bipyramids. There is two shorter (1.88 Å) and four longer (1.94 Å) Al–O bond length. Si is bonded to four O atoms to form SiO4 tetrahedra that share corners with two equivalent AlO6 octahedra, corners with two equivalent SiO4 tetrahedra, and a cornercorner with one CuO5 trigonal bipyramid. The corner-sharing octahedra tilt angles range from 37–49°. There are a spread of Si–O bond distances ranging from 1.60–1.67 Å. There are six inequivalent O sites. In the first O site, O is bonded in a distorted bent 150 degrees geometry to two equivalent Ca and two equivalent Si atoms. In the second O site, O is bonded in a bent 150 degrees geometry to two equivalent Si atoms. In the third O site, O is bonded in a trigonal non-coplanar geometry to two equivalent Ca and one Cu atom. In the fourth O site, O is bonded in a distorted trigonal planar geometry to one Cu, one Al, and one Si atom. In the fifth O site, O is bonded in a distorted trigonal non-coplanar geometry to one Ca, one Cu, and one Al atom. In the sixth O site, O is bonded in a 3-coordinate geometry to one Ca, one Al, and one Si atom.