Materials Data on KNb2O5 by Materials Project
KNb2O5 crystallizes in the monoclinic Pc space group. The structure is three-dimensional. there are three inequivalent K1+ sites. In the first K1+ site, K1+ is bonded to twelve O2- atoms to form KO12 cuboctahedra that share corners with two equivalent NbO6 pentagonal pyramids, faces with two equivalent KO12 cuboctahedra, and faces with eight NbO6 octahedra. There are a spread of K–O bond distances ranging from 2.80–3.10 Å. In the second K1+ site, K1+ is bonded in a 5-coordinate geometry to five O2- atoms. There are a spread of K–O bond distances ranging from 2.88–3.04 Å. In the third K1+ site, K1+ is bonded in a 1-coordinate geometry to five O2- atoms. There are a spread of K–O bond distances ranging from 2.81–3.06 Å. There are six inequivalent Nb+4.50+ sites. In the first Nb+4.50+ site, Nb+4.50+ is bonded to six O2- atoms to form a mixture of distorted face and corner-sharing NbO6 octahedra. The corner-sharing octahedra tilt angles range from 19–39°. There are a spread of Nb–O bond distances ranging from 1.87–2.25 Å. In the second Nb+4.50+ site, Nb+4.50+ is bonded to six O2- atoms to form NbO6 octahedra that share corners with six NbO6 octahedra, a cornercorner with one NbO6 pentagonal pyramid, faces with two equivalent KO12 cuboctahedra, and a faceface with one NbO6 pentagonal pyramid. The corner-sharing octahedra tilt angles range from 5–27°. There are a spread of Nb–O bond distances ranging from 2.00–2.13 Å. In the third Nb+4.50+ site, Nb+4.50+ is bonded to six O2- atoms to form distorted NbO6 pentagonal pyramids that share corners with two equivalent KO12 cuboctahedra, corners with three NbO6 octahedra, and faces with three NbO6 octahedra. The corner-sharing octahedra tilt angles range from 63–66°. There are a spread of Nb–O bond distances ranging from 2.10–2.22 Å. In the fourth Nb+4.50+ site, Nb+4.50+ is bonded to six O2- atoms to form NbO6 octahedra that share corners with six NbO6 octahedra, a cornercorner with one NbO6 pentagonal pyramid, faces with two equivalent KO12 cuboctahedra, and a faceface with one NbO6 pentagonal pyramid. The corner-sharing octahedra tilt angles range from 5–27°. There are a spread of Nb–O bond distances ranging from 1.90–2.16 Å. In the fifth Nb+4.50+ site, Nb+4.50+ is bonded to six O2- atoms to form distorted NbO6 octahedra that share corners with six NbO6 octahedra and faces with two equivalent KO12 cuboctahedra. The corner-sharing octahedra tilt angles range from 6–39°. There are a spread of Nb–O bond distances ranging from 1.85–2.28 Å. In the sixth Nb+4.50+ site, Nb+4.50+ is bonded to six O2- atoms to form NbO6 octahedra that share corners with six NbO6 octahedra and faces with two equivalent KO12 cuboctahedra. The corner-sharing octahedra tilt angles range from 2–38°. There are a spread of Nb–O bond distances ranging from 1.85–2.27 Å. There are fifteen inequivalent O2- sites. In the first O2- site, O2- is bonded in a 3-coordinate geometry to three Nb+4.50+ atoms. In the second O2- site, O2- is bonded in a 3-coordinate geometry to one K1+ and three Nb+4.50+ atoms. In the third O2- site, O2- is bonded in a 2-coordinate geometry to two equivalent K1+ and two Nb+4.50+ atoms. In the fourth O2- site, O2- is bonded in a 3-coordinate geometry to one K1+ and three Nb+4.50+ atoms. In the fifth O2- site, O2- is bonded in a distorted linear geometry to two equivalent K1+ and two Nb+4.50+ atoms. In the sixth O2- site, O2- is bonded in a 3-coordinate geometry to one K1+ and three Nb+4.50+ atoms. In the seventh O2- site, O2- is bonded in a 5-coordinate geometry to two equivalent K1+ and three Nb+4.50+ atoms. In the eighth O2- site, O2- is bonded in a 3-coordinate geometry to one K1+ and three Nb+4.50+ atoms. In the ninth O2- site, O2- is bonded in a 2-coordinate geometry to two equivalent K1+ and two Nb+4.50+ atoms. In the tenth O2- site, O2- is bonded in a distorted linear geometry to two equivalent K1+ and two Nb+4.50+ atoms. In the eleventh O2- site, O2- is bonded in a 1-coordinate geometry to one K1+ and two equivalent Nb+4.50+ atoms. In the twelfth O2- site, O2- is bonded in a 2-coordinate geometry to two equivalent K1+ and two Nb+4.50+ atoms. In the thirteenth O2- site, O2- is bonded in a distorted bent 150 degrees geometry to two equivalent K1+ and two Nb+4.50+ atoms. In the fourteenth O2- site, O2- is bonded in a 2-coordinate geometry to two equivalent K1+ and two Nb+4.50+ atoms. In the fifteenth O2- site, O2- is bonded in a 1-coordinate geometry to one K1+ and two equivalent Nb+4.50+ atoms.