Materials Data on KNaCaTh(Si2O5)4 by Materials Project

Abstract

KNaCaTh(Si8O20) crystallizes in the tetragonal P-42c space group. The structure is three-dimensional. K1+ is bonded to twelve O2- atoms to form KO12 cuboctahedra that share corners with four equivalent NaO8 hexagonal bipyramids and edges with eight SiO4 tetrahedra. There are a spread of K–O bond distances ranging from 2.96–3.22 Å. Na1+ is bonded to eight O2- atoms to form distorted NaO8 hexagonal bipyramids that share corners with four equivalent KO12 cuboctahedra, corners with four equivalent SiO4 tetrahedra, and edges with four equivalent SiO4 tetrahedra. There are four shorter (2.51 Å) and four longer (2.66 Å) Na–O bond lengths. Ca2+ is bonded in a 8-coordinate geometry to eight O2- atoms. There are four shorter (2.41 Å) and four longer (2.62 Å) Ca–O bond lengths. Th4+ is bonded in a 8-coordinate geometry to eight O2- atoms. There are four shorter (2.40 Å) and four longer (2.45 Å) Th–O bond lengths. 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 SiO4 tetrahedra, an edgeedge with one KO12 cuboctahedra, and an edgeedge with one NaO8 hexagonal bipyramid. There are a spread of Si–O bond distances ranging from 1.59–1.66 Å. In the second Si4+ site, Si4+ is bonded to four O2- atoms to form SiO4 tetrahedra that share a cornercorner with one NaO8 hexagonal bipyramid, corners with three equivalent SiO4 tetrahedra, and an edgeedge with one KO12 cuboctahedra. There are a spread of Si–O bond distances ranging from 1.60–1.66 Å. There are five inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one K1+ and two Si4+ atoms. In the second O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one Ca2+ and two Si4+ atoms. In the third O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one Na1+ and two Si4+ atoms. In the fourth O2- site, O2- is bonded in a 1-coordinate geometry to one K1+, one Na1+, one Th4+, and one Si4+ atom. In the fifth O2- site, O2- is bonded in a 1-coordinate geometry to one K1+, one Ca2+, one Th4+, and one Si4+ atom.