DOE OSTI2020
Na2BaSi2O6 crystallizes in the monoclinic P2_1 space group. The structure is three-dimensional. there are two inequivalent Na1+ sites. In the first Na1+ site, Na1+ is bonded to five O2- atoms to form distorted NaO5 trigonal bipyramids that share a cornercorner with one BaO8 hexagonal bipyramid, corners with four SiO4 tetrahedra, corners with two equivalent NaO5 trigonal bipyramids, an edgeedge with one SiO4 tetrahedra, and edges with two equivalent NaO5 trigonal bipyramids. There are a spread of Na–O bond distances ranging from 2.30–2.57 Å. In the second Na1+ site, Na1+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of Na–O bond distances ranging from 2.38–2.82 Å. Ba2+ is bonded to eight O2- atoms to form distorted BaO8 hexagonal bipyramids that share corners with five SiO4 tetrahedra, a cornercorner with one NaO5 trigonal bipyramid, edges with six equivalent BaO8 hexagonal bipyramids, and edges with two equivalent SiO4 tetrahedra. There are a spread of Ba–O bond distances ranging from 2.73–3.10 Å. There are two inequivalent Si4+ sites. In the first Si4+ site, Si4+ is bonded to four O2- atoms to form SiO4 tetrahedra that share corners with three equivalent BaO8 hexagonal bipyramids, corners with two equivalent SiO4 tetrahedra, a cornercorner with one NaO5 trigonal bipyramid, and edges with two equivalent BaO8 hexagonal bipyramids. There is two shorter (1.62 Å) and two longer (1.68 Å) Si–O bond length. In the second Si4+ site, Si4+ is bonded to four O2- atoms to form SiO4 tetrahedra that share corners with two equivalent BaO8 hexagonal bipyramids, corners with two equivalent SiO4 tetrahedra, corners with three equivalent NaO5 trigonal bipyramids, and an edgeedge with one NaO5 trigonal bipyramid. There are a spread of Si–O bond distances ranging from 1.61–1.69 Å. There are six inequivalent O2- sites. In the first O2- site, O2- is bonded in a 5-coordinate geometry to three Na1+, one Ba2+, and one Si4+ atom. In the second O2- site, O2- is bonded in a 4-coordinate geometry to two Na1+ and two Si4+ atoms. In the third O2- site, O2- is bonded in a 5-coordinate geometry to four Na1+ and one Si4+ atom. In the fourth O2- site, O2- is bonded in a distorted single-bond geometry to one Na1+, three equivalent Ba2+, and one Si4+ atom. In the fifth O2- site, O2- is bonded in a distorted single-bond geometry to one Na1+, three equivalent Ba2+, and one Si4+ atom. In the sixth O2- site, O2- is bonded in a distorted bent 120 degrees geometry to one Ba2+ and two Si4+ atoms.