Materials Data on K3NbAs2O9 by Materials Project
K3NbAs2O9 crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. there are three inequivalent K1+ sites. In the first K1+ site, K1+ is bonded to seven O2- atoms to form distorted KO7 hexagonal pyramids that share corners with two equivalent KO7 hexagonal pyramids, a cornercorner with one AsO4 tetrahedra, edges with three equivalent NbO6 octahedra, and edges with three AsO4 tetrahedra. There are a spread of K–O bond distances ranging from 2.74–2.86 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 2.76–3.41 Å. In the third 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 2.57–3.30 Å. Nb5+ is bonded to six O2- atoms to form distorted NbO6 octahedra that share corners with five AsO4 tetrahedra and edges with three equivalent KO7 hexagonal pyramids. There are a spread of Nb–O bond distances ranging from 1.77–2.42 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 two equivalent NbO6 octahedra and an edgeedge with one KO7 hexagonal pyramid. The corner-sharing octahedral tilt angles are 32°. There are a spread of As–O bond distances ranging from 1.68–1.77 Å. In the second As5+ site, As5+ is bonded to four O2- atoms to form AsO4 tetrahedra that share a cornercorner with one KO7 hexagonal pyramid, corners with three equivalent NbO6 octahedra, and edges with two equivalent KO7 hexagonal pyramids. The corner-sharing octahedra tilt angles range from 32–34°. There are a spread of As–O bond distances ranging from 1.69–1.75 Å. There are seven inequivalent O2- sites. In the first O2- site, O2- is bonded in a 1-coordinate geometry to four K1+ and one As5+ atom. In the second O2- site, O2- is bonded in a 2-coordinate geometry to three K1+ and one As5+ atom. In the third O2- site, O2- is bonded in a 1-coordinate geometry to four K1+ and one As5+ atom. In the fourth O2- site, O2- is bonded in a 1-coordinate geometry to three K1+, one Nb5+, and one As5+ atom. In the fifth O2- site, O2- is bonded in a distorted bent 150 degrees geometry to two K1+, one Nb5+, and one As5+ atom. In the sixth O2- site, O2- is bonded in a distorted single-bond geometry to four K1+ and one Nb5+ atom. In the seventh O2- site, O2- is bonded in a 2-coordinate geometry to one K1+, one Nb5+, and one As5+ atom.