DOI: 10.17188/1322718
title: Materials Data on MgCoNi2O7 by Materials Project

description: MgCoNi2O7 crystallizes in the monoclinic P2_1/c space group. The structure is three-dimensional. there are two inequivalent Mg2+ sites. In the first Mg2+ site, Mg2+ is bonded in a 5-coordinate geometry to five O2- atoms. There are a spread of Mg–O bond distances ranging from 2.09–2.30 Å. In the second Mg2+ site, Mg2+ is bonded to six O2- atoms to form distorted MgO6 octahedra that share a cornercorner with one NiO6 pentagonal pyramid, corners with two equivalent NiO5 square pyramids, a cornercorner with one NiO5 trigonal bipyramid, edges with two CoO6 octahedra, and an edgeedge with one NiO6 pentagonal pyramid. There are a spread of Mg–O bond distances ranging from 2.02–2.27 Å. There are two inequivalent Co4+ sites. In the first Co4+ site, Co4+ is bonded to six O2- atoms to form CoO6 octahedra that share corners with two equivalent NiO5 square pyramids, corners with two equivalent NiO5 trigonal bipyramids, an edgeedge with one MgO6 octahedra, an edgeedge with one CoO6 octahedra, and edges with two equivalent NiO6 pentagonal pyramids. There are a spread of Co–O bond distances ranging from 1.76–1.98 Å. In the second Co4+ site, Co4+ is bonded to six O2- atoms to form CoO6 octahedra that share corners with two equivalent NiO6 pentagonal pyramids, a cornercorner with one NiO5 square pyramid, an edgeedge with one MgO6 octahedra, an edgeedge with one CoO6 octahedra, and an edgeedge with one NiO5 square pyramid. There are a spread of Co–O bond distances ranging from 1.78–1.95 Å. There are four inequivalent Ni4+ sites. In the first Ni4+ site, Ni4+ is bonded in a distorted rectangular see-saw-like geometry to four O2- atoms. There are a spread of Ni–O bond distances ranging from 1.86–2.04 Å. In the second Ni4+ site, Ni4+ is bonded to five O2- atoms to form NiO5 trigonal bipyramids that share a cornercorner with one MgO6 octahedra, corners with two equivalent CoO6 octahedra, a cornercorner with one NiO5 square pyramid, and an edgeedge with one NiO6 pentagonal pyramid. The corner-sharing octahedra tilt angles range from 41–64°. There are a spread of Ni–O bond distances ranging from 1.79–1.95 Å. In the third Ni4+ site, Ni4+ is bonded to six O2- atoms to form distorted NiO6 pentagonal pyramids that share a cornercorner with one MgO6 octahedra, corners with two equivalent CoO6 octahedra, an edgeedge with one MgO6 octahedra, edges with two equivalent CoO6 octahedra, an edgeedge with one NiO5 square pyramid, and an edgeedge with one NiO5 trigonal bipyramid. The corner-sharing octahedra tilt angles range from 27–65°. There are a spread of Ni–O bond distances ranging from 1.94–2.23 Å. In the fourth Ni4+ site, Ni4+ is bonded to five O2- atoms to form distorted NiO5 square pyramids that share corners with two equivalent MgO6 octahedra, corners with three CoO6 octahedra, a cornercorner with one NiO5 trigonal bipyramid, an edgeedge with one CoO6 octahedra, and an edgeedge with one NiO6 pentagonal pyramid. The corner-sharing octahedra tilt angles range from 30–73°. There are a spread of Ni–O bond distances ranging from 1.85–1.99 Å. There are fourteen inequivalent O2- sites. In the first O2- site, O2- is bonded in a 3-coordinate geometry to one Mg2+, one Ni4+, and one O2- atom. The O–O bond length is 1.33 Å. In the second O2- site, O2- is bonded in a 4-coordinate geometry to one Mg2+, one Co4+, and one Ni4+ atom. In the third O2- site, O2- is bonded in a bent 120 degrees geometry to one Co4+ and one Ni4+ atom. In the fourth O2- site, O2- is bonded to one Mg2+, one Co4+, and two Ni4+ atoms to form corner-sharing OMgCoNi2 tetrahedra. In the fifth O2- site, O2- is bonded in a distorted trigonal planar geometry to one Mg2+, one Co4+, and one Ni4+ atom. In the sixth O2- site, O2- is bonded to one Mg2+, two Co4+, and one Ni4+ atom to form distorted corner-sharing OMgCo2Ni tetrahedra. In the seventh O2- site, O2- is bonded in a distorted trigonal planar geometry to one Mg2+, one Co4+, and one Ni4+ atom. In the eighth O2- site, O2- is bonded in a trigonal non-coplanar geometry to two Mg2+ and one Ni4+ atom. In the ninth O2- site, O2- is bonded in a 3-coordinate geometry to one Mg2+ and two Ni4+ atoms. In the tenth O2- site, O2- is bonded in a 3-coordinate geometry to two Ni4+ and one O2- atom. In the eleventh O2- site, O2- is bonded in a distorted T-shaped geometry to two Co4+ and one Ni4+ atom. In the twelfth O2- site, O2- is bonded in a rectangular see-saw-like geometry to one Mg2+, one Co4+, and two Ni4+ atoms. In the thirteenth O2- site, O2- is bonded in a distorted see-saw-like geometry to one Mg2+, one Co4+, and two Ni4+ atoms. In the fourteenth O2- site, O2- is bonded in a distorted trigonal non-coplanar geometry to one Co4+ and two Ni4+ atoms.