Materials Data on Nb2Fe4O9 by Materials Project
Fe4Nb2O9 is Ilmenite-like structured and crystallizes in the trigonal P-3c1 space group. The structure is three-dimensional. Nb+3.50+ is bonded to six O2- atoms to form distorted NbO6 octahedra that share corners with nine FeO6 octahedra, edges with three equivalent FeO6 octahedra, and a faceface with one NbO6 octahedra. The corner-sharing octahedra tilt angles range from 47–57°. There are three shorter (1.93 Å) and three longer (2.17 Å) Nb–O bond lengths. There are two inequivalent Fe+2.75+ sites. In the first Fe+2.75+ site, Fe+2.75+ is bonded to six equivalent O2- atoms to form FeO6 octahedra that share corners with three equivalent FeO6 octahedra, corners with six equivalent NbO6 octahedra, edges with three equivalent FeO6 octahedra, and a faceface with one FeO6 octahedra. The corner-sharing octahedra tilt angles range from 47–57°. There are three shorter (2.13 Å) and three longer (2.22 Å) Fe–O bond lengths. In the second Fe+2.75+ site, Fe+2.75+ is bonded to six O2- atoms to form distorted FeO6 octahedra that share corners with three equivalent NbO6 octahedra, corners with six FeO6 octahedra, edges with three equivalent NbO6 octahedra, and a faceface with one FeO6 octahedra. The corner-sharing octahedra tilt angles range from 48–67°. There are three shorter (2.09 Å) and three longer (2.31 Å) Fe–O bond lengths. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded in a 4-coordinate geometry to one Nb+3.50+ and three Fe+2.75+ atoms. In the second O2- site, O2- is bonded to two equivalent Nb+3.50+ and two equivalent Fe+2.75+ atoms to form a mixture of distorted edge and corner-sharing ONb2Fe2 trigonal pyramids.