Materials Data on K2CaAs2O7 by Materials Project
K2CaAs2O7 crystallizes in the monoclinic P2_1/c space group. The structure is three-dimensional. there are two inequivalent K1+ sites. In the first K1+ site, K1+ is bonded in a 9-coordinate geometry to nine O2- atoms. There are a spread of K–O bond distances ranging from 2.85–3.23 Å. In the second K1+ site, K1+ is bonded in a 9-coordinate geometry to nine O2- atoms. There are a spread of K–O bond distances ranging from 2.79–3.34 Å. Ca2+ is bonded to six O2- atoms to form CaO6 octahedra that share corners with six AsO4 tetrahedra. There are a spread of Ca–O bond distances ranging from 2.34–2.43 Å. There are two inequivalent As5+ sites. In the first As5+ site, As5+ is bonded to four O2- atoms to form AsO4 tetrahedra that share corners with three equivalent CaO6 octahedra and a cornercorner with one AsO4 tetrahedra. The corner-sharing octahedra tilt angles range from 30–50°. There are a spread of As–O bond distances ranging from 1.70–1.83 Å. In the second As5+ site, As5+ is bonded to four O2- atoms to form AsO4 tetrahedra that share corners with three equivalent CaO6 octahedra and a cornercorner with one AsO4 tetrahedra. The corner-sharing octahedra tilt angles range from 19–51°. There are a spread of As–O bond distances ranging from 1.69–1.83 Å. There are seven inequivalent O2- sites. In the first O2- site, O2- is bonded in a 1-coordinate geometry to three K1+, one Ca2+, and one As5+ atom. In the second O2- site, O2- is bonded in a 2-coordinate geometry to three equivalent K1+, one Ca2+, and one As5+ atom. In the third O2- site, O2- is bonded in a 2-coordinate geometry to two K1+, one Ca2+, and one As5+ atom. In the fourth O2- site, O2- is bonded in a 2-coordinate geometry to three equivalent K1+, one Ca2+, and one As5+ atom. In the fifth O2- site, O2- is bonded in a 2-coordinate geometry to two K1+, one Ca2+, and one As5+ atom. In the sixth O2- site, O2- is bonded in a distorted bent 120 degrees geometry to two equivalent K1+ and two As5+ atoms. In the seventh O2- site, O2- is bonded in a 5-coordinate geometry to three K1+, one Ca2+, and one As5+ atom.