Materials Data on KNb2PO8 by Materials Project
KNb2PO8 crystallizes in the trigonal R3 space group. The structure is three-dimensional. K1+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of K–O bond distances ranging from 2.91–3.29 Å. There are two inequivalent Nb5+ sites. In the first Nb5+ site, Nb5+ is bonded to six O2- atoms to form NbO6 octahedra that share corners with four NbO6 octahedra and corners with two equivalent PO4 tetrahedra. The corner-sharing octahedra tilt angles range from 4–38°. There are a spread of Nb–O bond distances ranging from 1.89–2.13 Å. In the second Nb5+ site, Nb5+ is bonded to six O2- atoms to form NbO6 octahedra that share corners with four NbO6 octahedra and corners with two equivalent PO4 tetrahedra. The corner-sharing octahedra tilt angles range from 4–39°. There are a spread of Nb–O bond distances ranging from 1.90–2.13 Å. P5+ is bonded to four O2- atoms to form PO4 tetrahedra that share corners with four NbO6 octahedra. The corner-sharing octahedra tilt angles range from 36–41°. There is one shorter (1.54 Å) and three longer (1.55 Å) P–O bond length. There are eight inequivalent O2- sites. In the first O2- site, O2- is bonded in a bent 150 degrees geometry to one K1+ and two Nb5+ atoms. In the second O2- site, O2- is bonded in a linear geometry to two Nb5+ atoms. In the third O2- site, O2- is bonded in a 2-coordinate geometry to one K1+, one Nb5+, and one P5+ atom. In the fourth O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one K1+ and two equivalent Nb5+ atoms. In the fifth O2- site, O2- is bonded in a 2-coordinate geometry to one K1+, one Nb5+, and one P5+ atom. In the sixth O2- site, O2- is bonded in a bent 150 degrees geometry to one Nb5+ and one P5+ atom. In the seventh O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one K1+, one Nb5+, and one P5+ atom. In the eighth O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one K1+ and two equivalent Nb5+ atoms.