Materials Data on K3GdSi2O7 by Materials Project
K3GdSi2O7 crystallizes in the hexagonal P6_3/mcm space group. The structure is three-dimensional. there are three inequivalent K1+ sites. In the first K1+ site, K1+ is bonded in a 8-coordinate geometry to eight O2- atoms. There are a spread of K–O bond distances ranging from 2.80–3.07 Å. In the second K1+ site, K1+ is bonded in a 9-coordinate geometry to nine O2- atoms. There are six shorter (2.95 Å) and three longer (3.05 Å) K–O bond lengths. In the third K1+ site, K1+ is bonded in a distorted hexagonal planar geometry to six equivalent O2- atoms. All K–O bond lengths are 2.78 Å. There are two inequivalent Gd3+ sites. In the first Gd3+ site, Gd3+ is bonded to six equivalent O2- atoms to form GdO6 octahedra that share corners with six equivalent SiO4 tetrahedra. All Gd–O bond lengths are 2.29 Å. In the second Gd3+ site, Gd3+ is bonded to six equivalent O2- atoms to form distorted GdO6 pentagonal pyramids that share corners with six equivalent SiO4 tetrahedra. All Gd–O bond lengths are 2.33 Å. Si4+ is bonded to four O2- atoms to form SiO4 tetrahedra that share corners with two equivalent GdO6 octahedra, a cornercorner with one GdO6 pentagonal pyramid, and a cornercorner with one SiO4 tetrahedra. The corner-sharing octahedral tilt angles are 12°. There is three shorter (1.64 Å) and one longer (1.69 Å) Si–O bond length. There are three inequivalent O2- sites. In the first O2- site, O2- is bonded in a 6-coordinate geometry to four K1+, one Gd3+, and one Si4+ atom. In the second O2- site, O2- is bonded in a 1-coordinate geometry to three K1+, one Gd3+, and one Si4+ atom. In the third O2- site, O2- is bonded in a 2-coordinate geometry to two equivalent K1+ and two equivalent Si4+ atoms.