Materials Data on Ca3HfSi2O9 by Materials Project
Ca3HfSi2O9 crystallizes in the monoclinic P2_1/c space group. The structure is three-dimensional. there are three inequivalent Ca2+ sites. In the first Ca2+ site, Ca2+ is bonded in a 7-coordinate geometry to seven O2- atoms. There are a spread of Ca–O bond distances ranging from 2.34–2.70 Å. In the second Ca2+ site, Ca2+ is bonded in a 6-coordinate geometry to seven O2- atoms. There are a spread of Ca–O bond distances ranging from 2.34–3.00 Å. In the third Ca2+ site, Ca2+ is bonded in a 7-coordinate geometry to seven O2- atoms. There are a spread of Ca–O bond distances ranging from 2.34–2.73 Å. Hf4+ is bonded to six O2- atoms to form HfO6 octahedra that share corners with three SiO4 tetrahedra and an edgeedge with one HfO6 octahedra. There are a spread of Hf–O bond distances ranging from 2.00–2.19 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 a cornercorner with one HfO6 octahedra and a cornercorner with one SiO4 tetrahedra. The corner-sharing octahedral tilt angles are 41°. There are a spread of Si–O bond distances ranging from 1.62–1.68 Å. In the second Si4+ site, Si4+ is bonded to four O2- atoms to form SiO4 tetrahedra that share corners with two equivalent HfO6 octahedra and a cornercorner with one SiO4 tetrahedra. The corner-sharing octahedra tilt angles range from 37–61°. There are a spread of Si–O bond distances ranging from 1.61–1.67 Å. There are nine inequivalent O2- sites. In the first O2- site, O2- is bonded in a 4-coordinate geometry to three Ca2+ and one Si4+ atom. In the second O2- site, O2- is bonded in a 3-coordinate geometry to one Ca2+, one Hf4+, and one Si4+ atom. In the third O2- site, O2- is bonded in a 3-coordinate geometry to three Ca2+ and one Si4+ atom. In the fourth O2- site, O2- is bonded to three Ca2+ and one Si4+ atom to form distorted corner-sharing OCa3Si tetrahedra. In the fifth O2- site, O2- is bonded in a 4-coordinate geometry to two Ca2+, one Hf4+, and one Si4+ atom. In the sixth O2- site, O2- is bonded in a distorted bent 150 degrees geometry to two Ca2+ and two Si4+ atoms. In the seventh O2- site, O2- is bonded in a 4-coordinate geometry to two Ca2+, one Hf4+, and one Si4+ atom. In the eighth O2- site, O2- is bonded to three Ca2+ and one Hf4+ atom to form distorted OCa3Hf tetrahedra that share corners with five OCa3Si tetrahedra and edges with two OCa3Hf tetrahedra. In the ninth O2- site, O2- is bonded to two Ca2+ and two equivalent Hf4+ atoms to form distorted OCa2Hf2 tetrahedra that share corners with four OCa3Si tetrahedra and edges with two OCa3Hf tetrahedra.