DOE OSTI2020
Cd2Nb2O7 crystallizes in the orthorhombic Ima2 space group. The structure is three-dimensional. 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 six NbO6 octahedra and edges with six CdO8 hexagonal bipyramids. The corner-sharing octahedra tilt angles range from 33–51°. There are a spread of Nb–O bond distances ranging from 1.90–2.15 Å. In the second Nb5+ site, Nb5+ is bonded to six O2- atoms to form NbO6 octahedra that share corners with six NbO6 octahedra and edges with six CdO8 hexagonal bipyramids. The corner-sharing octahedra tilt angles range from 33–51°. There are a spread of Nb–O bond distances ranging from 1.91–2.12 Å. There are two inequivalent Cd2+ sites. In the first Cd2+ site, Cd2+ is bonded to eight O2- atoms to form distorted CdO8 hexagonal bipyramids that share edges with six CdO8 hexagonal bipyramids and edges with six NbO6 octahedra. There are a spread of Cd–O bond distances ranging from 2.30–2.84 Å. In the second Cd2+ site, Cd2+ is bonded to eight O2- atoms to form distorted CdO8 hexagonal bipyramids that share edges with six CdO8 hexagonal bipyramids and edges with six NbO6 octahedra. There are a spread of Cd–O bond distances ranging from 2.29–2.87 Å. There are five inequivalent O2- sites. In the first O2- site, O2- is bonded in a 4-coordinate geometry to two Nb5+ and two Cd2+ atoms. In the second O2- site, O2- is bonded to four Cd2+ atoms to form corner-sharing OCd4 tetrahedra. In the third O2- site, O2- is bonded in a 2-coordinate geometry to two equivalent Nb5+ and two equivalent Cd2+ atoms. In the fourth O2- site, O2- is bonded in a 4-coordinate geometry to two equivalent Nb5+ and two equivalent Cd2+ atoms. In the fifth O2- site, O2- is bonded in a distorted bent 150 degrees geometry to two Nb5+ and two Cd2+ atoms.