DOE OSTI2020
TiNb2O7 crystallizes in the monoclinic Cm space group. The structure is three-dimensional. there are three inequivalent Ti4+ sites. In the first Ti4+ site, Ti4+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of Ti–O bond distances ranging from 1.74–2.28 Å. In the second Ti4+ site, Ti4+ is bonded to six O2- atoms to form distorted TiO6 octahedra that share corners with two equivalent TiO6 octahedra, corners with two NbO6 octahedra, edges with two equivalent TiO6 octahedra, and edges with two equivalent NbO6 octahedra. The corner-sharing octahedra tilt angles range from 4–29°. There are a spread of Ti–O bond distances ranging from 1.79–2.21 Å. In the third Ti4+ site, Ti4+ is bonded to six O2- atoms to form distorted TiO6 octahedra that share corners with two equivalent TiO6 octahedra, corners with two NbO6 octahedra, edges with two equivalent TiO6 octahedra, and edges with two NbO6 octahedra. The corner-sharing octahedra tilt angles range from 3–30°. There are a spread of Ti–O bond distances ranging from 1.83–2.28 Å. There are six inequivalent Nb5+ sites. In the first Nb5+ site, Nb5+ is bonded to six O2- atoms to form distorted NbO6 octahedra that share a cornercorner with one TiO6 octahedra, corners with three NbO6 octahedra, and edges with two equivalent NbO6 octahedra. The corner-sharing octahedra tilt angles range from 3–31°. There are a spread of Nb–O bond distances ranging from 1.85–2.26 Å. In the second Nb5+ site, Nb5+ is bonded to six O2- atoms to form NbO6 octahedra that share a cornercorner with one TiO6 octahedra, corners with four NbO6 octahedra, and edges with two equivalent NbO6 octahedra. The corner-sharing octahedra tilt angles range from 4–30°. There are a spread of Nb–O bond distances ranging from 1.84–2.25 Å. In the third Nb5+ site, Nb5+ is bonded to six O2- atoms to form distorted NbO6 octahedra that share corners with two TiO6 octahedra, corners with three NbO6 octahedra, and an edgeedge with one NbO6 octahedra. The corner-sharing octahedra tilt angles range from 6–30°. There are a spread of Nb–O bond distances ranging from 1.87–2.33 Å. In the fourth Nb5+ site, Nb5+ is bonded to six O2- atoms to form distorted NbO6 octahedra that share corners with four NbO6 octahedra and edges with three TiO6 octahedra. The corner-sharing octahedra tilt angles range from 15–30°. There are a spread of Nb–O bond distances ranging from 1.84–2.32 Å. In the fifth Nb5+ site, Nb5+ is bonded to six O2- atoms to form corner-sharing NbO6 octahedra. The corner-sharing octahedra tilt angles range from 2–15°. There are a spread of Nb–O bond distances ranging from 1.93–2.08 Å. In the sixth Nb5+ site, Nb5+ is bonded to six O2- atoms to form distorted NbO6 octahedra that share corners with four NbO6 octahedra, an edgeedge with one TiO6 octahedra, and an edgeedge with one NbO6 octahedra. The corner-sharing octahedra tilt angles range from 4–30°. There are a spread of Nb–O bond distances ranging from 1.87–2.26 Å. There are twenty-one inequivalent O2- sites. In the first O2- site, O2- is bonded in a linear geometry to 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 3-coordinate geometry to one Ti4+ and two equivalent Nb5+ atoms. In the fourth O2- site, O2- is bonded in a 3-coordinate geometry to one Ti4+ and two equivalent Nb5+ atoms. In the fifth O2- site, O2- is bonded in a 3-coordinate geometry to three Nb5+ atoms. In the sixth O2- site, O2- is bonded in a 3-coordinate geometry to three Nb5+ atoms. In the seventh O2- site, O2- is bonded in a linear geometry to two Nb5+ atoms. In the eighth O2- site, O2- is bonded in a linear geometry to two Nb5+ atoms. In the ninth O2- site, O2- is bonded in a linear geometry to one Ti4+ and one Nb5+ atom. In the tenth O2- site, O2- is bonded in a linear geometry to one Ti4+ and one Nb5+ atom. In the eleventh O2- site, O2- is bonded in a 4-coordinate geometry to three Ti4+ and one Nb5+ atom. In the twelfth O2- site, O2- is bonded to two equivalent Ti4+ and two Nb5+ atoms to form distorted corner-sharing OTi2Nb2 tetrahedra. In the thirteenth O2- site, O2- is bonded in a 3-coordinate geometry to one Ti4+ and two Nb5+ atoms. In the fourteenth O2- site, O2- is bonded in a 3-coordinate geometry to one Ti4+ and two Nb5+ atoms. In the fifteenth O2- site, O2- is bonded in a linear geometry to two Nb5+ atoms. In the sixteenth O2- site, O2- is bonded in a linear geometry to one Ti4+ and one Nb5+ atom. In the seventeenth O2- site, O2- is bonded in a distorted trigonal non-coplanar geometry to three Ti4+ atoms. In the eighteenth O2- site, O2- is bonded in a 3-coordinate geometry to one Ti4+ and two equivalent Nb5+ atoms. In the nineteenth O2- site, O2- is bonded in a linear geometry to two equivalent Nb5+ atoms. In the twentieth O2- site, O2- is bonded in a linear geometry to one Ti4+ and one Nb5+ atom. In the twenty-first O2- site, O2- is bonded in a linear geometry to one Ti4+ and one Nb5+ atom.