Materials Data on CaSO4 by Materials Project

Abstract

CaSO4 is Zircon-like structured and crystallizes in the orthorhombic C222 space group. The structure is three-dimensional. there are two inequivalent Ca2+ sites. In the first Ca2+ site, Ca2+ is bonded to eight O2- atoms to form distorted CaO8 hexagonal bipyramids that share corners with four SO4 tetrahedra, edges with four CaO8 hexagonal bipyramids, and edges with two equivalent SO4 tetrahedra. There are a spread of Ca–O bond distances ranging from 2.40–2.57 Å. In the second Ca2+ site, Ca2+ is bonded to eight O2- atoms to form distorted CaO8 hexagonal bipyramids that share corners with four equivalent SO4 tetrahedra, edges with four equivalent CaO8 hexagonal bipyramids, and edges with two equivalent SO4 tetrahedra. There are four shorter (2.41 Å) and four longer (2.57 Å) Ca–O bond lengths. There are two inequivalent S6+ sites. In the first S6+ site, S6+ is bonded to four O2- atoms to form SO4 tetrahedra that share corners with four CaO8 hexagonal bipyramids and edges with two equivalent CaO8 hexagonal bipyramids. All S–O bond lengths are 1.49 Å. In the second S6+ site, S6+ is bonded to four equivalent O2- atoms to form SO4 tetrahedra that share corners with four equivalent CaO8 hexagonal bipyramids and edges with two equivalent CaO8 hexagonal bipyramids. All S–O bond lengths are 1.49 Å. There are three inequivalent O2- sites. In the first O2- site, O2- is bonded in a 1-coordinate geometry to two Ca2+ and one S6+ atom. In the second O2- site, O2- is bonded in a 1-coordinate geometry to two Ca2+ and one S6+ atom. In the third O2- site, O2- is bonded in a 1-coordinate geometry to two equivalent Ca2+ and one S6+ atom.