Materials Data on MgFe4NiO8 by Materials Project
MgFe4NiO8 is Spinel-derived structured and crystallizes in the trigonal R3m space group. The structure is three-dimensional. Mg2+ is bonded to four O2- atoms to form MgO4 tetrahedra that share corners with three equivalent NiO6 octahedra and corners with nine equivalent FeO6 octahedra. The corner-sharing octahedra tilt angles range from 57–59°. There is three shorter (1.98 Å) and one longer (2.00 Å) Mg–O bond length. There are two inequivalent Fe3+ sites. In the first Fe3+ site, Fe3+ is bonded to six O2- atoms to form FeO6 octahedra that share corners with three equivalent MgO4 tetrahedra, corners with three equivalent FeO4 tetrahedra, edges with two equivalent NiO6 octahedra, and edges with four equivalent FeO6 octahedra. There are a spread of Fe–O bond distances ranging from 2.01–2.09 Å. In the second Fe3+ site, Fe3+ is bonded to four O2- atoms to form FeO4 tetrahedra that share corners with three equivalent NiO6 octahedra and corners with nine equivalent FeO6 octahedra. The corner-sharing octahedra tilt angles range from 57–58°. There is three shorter (1.93 Å) and one longer (1.97 Å) Fe–O bond length. Ni2+ is bonded to six O2- atoms to form NiO6 octahedra that share corners with three equivalent MgO4 tetrahedra, corners with three equivalent FeO4 tetrahedra, and edges with six equivalent FeO6 octahedra. There are three shorter (2.08 Å) and three longer (2.11 Å) Ni–O bond lengths. There are four inequivalent O2- sites. In the first O2- site, O2- is bonded to four Fe3+ atoms to form a mixture of distorted edge and corner-sharing OFe4 trigonal pyramids. In the second O2- site, O2- is bonded to three Fe3+ and one Ni2+ atom to form a mixture of distorted edge and corner-sharing OFe3Ni trigonal pyramids. In the third O2- site, O2- is bonded in a distorted rectangular see-saw-like geometry to one Mg2+ and three equivalent Fe3+ atoms. In the fourth O2- site, O2- is bonded in a rectangular see-saw-like geometry to one Mg2+, two equivalent Fe3+, and one Ni2+ atom.