Materials Data on BaCa2Mg(SiO4)2 by Materials Project

Abstract

BaCa2MgSi2O8 crystallizes in the trigonal P-3 space group. The structure is three-dimensional. Ba2+ is bonded to twelve O2- atoms to form BaO12 cuboctahedra that share edges with six equivalent BaO12 cuboctahedra, edges with six equivalent SiO4 tetrahedra, and faces with two equivalent MgO6 octahedra. There are six shorter (2.82 Å) and six longer (3.17 Å) Ba–O bond lengths. Ca2+ is bonded in a 4-coordinate geometry to four O2- atoms. There are one shorter (2.28 Å) and three longer (2.42 Å) Ca–O bond lengths. Mg2+ is bonded to six equivalent O2- atoms to form MgO6 octahedra that share corners with six equivalent SiO4 tetrahedra and faces with two equivalent BaO12 cuboctahedra. All Mg–O bond lengths are 2.10 Å. Si4+ is bonded to four O2- atoms to form SiO4 tetrahedra that share corners with three equivalent MgO6 octahedra and edges with three equivalent BaO12 cuboctahedra. The corner-sharing octahedral tilt angles are 24°. There is one shorter (1.62 Å) and three longer (1.66 Å) Si–O bond length. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted linear geometry to three equivalent Ba2+, one Ca2+, and one Si4+ atom. In the second O2- site, O2- is bonded in a 5-coordinate geometry to one Ba2+, one Ca2+, one Mg2+, and one Si4+ atom.