Materials Data on Ca4Ta2O9 by Materials Project
Ca3(CaTa2)O9 crystallizes in the triclinic P-1 space group. The structure is three-dimensional. there are five inequivalent Ca2+ sites. In the first Ca2+ site, Ca2+ is bonded in a 3-coordinate geometry to five O2- atoms. There are a spread of Ca–O bond distances ranging from 2.33–2.86 Å. In the second Ca2+ site, Ca2+ is bonded to six O2- atoms to form CaO6 octahedra that share corners with six equivalent CaO6 octahedra and corners with six equivalent TaO6 octahedra. The corner-sharing octahedra tilt angles range from 41–62°. There are two shorter (2.37 Å) and four longer (2.38 Å) Ca–O bond lengths. In the third Ca2+ site, Ca2+ is bonded to six O2- atoms to form CaO6 octahedra that share corners with six equivalent TaO6 octahedra. The corner-sharing octahedra tilt angles range from 35–37°. There are a spread of Ca–O bond distances ranging from 2.29–2.31 Å. In the fourth Ca2+ site, Ca2+ is bonded to six O2- atoms to form distorted CaO6 octahedra that share corners with three equivalent CaO6 octahedra, corners with three equivalent TaO6 octahedra, and edges with three equivalent TaO6 octahedra. The corner-sharing octahedra tilt angles range from 29–62°. There are a spread of Ca–O bond distances ranging from 2.34–2.43 Å. In the fifth Ca2+ site, Ca2+ is bonded in a distorted trigonal planar geometry to three O2- atoms. All Ca–O bond lengths are 2.25 Å. There are two inequivalent Ta5+ sites. In the first Ta5+ site, Ta5+ is bonded to six O2- atoms to form TaO6 octahedra that share corners with six CaO6 octahedra and a faceface with one TaO6 octahedra. The corner-sharing octahedra tilt angles range from 29–37°. There are a spread of Ta–O bond distances ranging from 1.92–2.12 Å. In the second Ta5+ site, Ta5+ is bonded to six O2- atoms to form distorted TaO6 octahedra that share corners with three equivalent CaO6 octahedra, edges with three equivalent CaO6 octahedra, and a faceface with one TaO6 octahedra. The corner-sharing octahedra tilt angles range from 41–42°. There are a spread of Ta–O bond distances ranging from 1.90–2.21 Å. There are nine inequivalent O2- sites. In the first O2- site, O2- is bonded in a 4-coordinate geometry to two Ca2+ and two Ta5+ atoms. In the second O2- site, O2- is bonded in a 4-coordinate geometry to two Ca2+ and one Ta5+ atom. In the third O2- site, O2- is bonded in a 3-coordinate geometry to two Ca2+ and one Ta5+ atom. In the fourth O2- site, O2- is bonded in a 4-coordinate geometry to three Ca2+ and one Ta5+ atom. In the fifth O2- site, O2- is bonded in a 3-coordinate geometry to two Ca2+ and one Ta5+ atom. In the sixth O2- site, O2- is bonded in a 4-coordinate geometry to two Ca2+ and two Ta5+ atoms. In the seventh O2- site, O2- is bonded in a 4-coordinate geometry to two Ca2+ and two Ta5+ atoms. In the eighth O2- site, O2- is bonded in a 3-coordinate geometry to two Ca2+ and one Ta5+ atom. In the ninth O2- site, O2- is bonded in a 4-coordinate geometry to three Ca2+ and one Ta5+ atom.