Materials Data on Mg4Nb2O9 by Materials Project

Mg4Nb2O9 is Ilmenite-like structured and crystallizes in the trigonal P-3c1 space group. The structure is three-dimensional. there are two inequivalent Mg2+ sites. In the first Mg2+ site, Mg2+ is bonded to six equivalent O2- atoms to form MgO6 octahedra that share corners with three equivalent MgO6 octahedra, corners with six equivalent NbO6 octahedra, edges with three equivalent MgO6 octahedra, and a faceface with one MgO6 octahedra. The corner-sharing octahedra tilt angles range from 47–59°. There are three shorter (2.09 Å) and three longer (2.17 Å) Mg–O bond lengths. In the second Mg2+ site, Mg2+ is bonded to six O2- atoms to form distorted MgO6 octahedra that share corners with three equivalent NbO6 octahedra, corners with six MgO6 octahedra, edges with three equivalent NbO6 octahedra, and a faceface with one MgO6 octahedra. The corner-sharing octahedra tilt angles range from 48–65°. There are three shorter (2.04 Å) and three longer (2.24 Å) Mg–O bond lengths. Nb5+ is bonded to six O2- atoms to form distorted NbO6 octahedra that share corners with nine MgO6 octahedra, edges with three equivalent MgO6 octahedra, and a faceface with one NbO6 octahedra. The corner-sharing octahedra tilt angles range from 47–59°. There are three shorter (1.93 Å) and three longer (2.16 Å) Nb–O bond lengths. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded to three Mg2+ and one Nb5+ atom to form a mixture of distorted corner and edge-sharing OMg3Nb trigonal pyramids. In the second O2- site, O2- is bonded to two equivalent Mg2+ and two equivalent Nb5+ atoms to form a mixture of distorted corner and edge-sharing OMg2Nb2 trigonal pyramids.