DOE OSTI2020
NiMn2O4 is Spinel-like structured and crystallizes in the monoclinic Cm space group. The structure is three-dimensional. there are six inequivalent Mn2+ sites. In the first Mn2+ site, Mn2+ is bonded to four O2- atoms to form MnO4 tetrahedra that share corners with six MnO6 octahedra and corners with six NiO6 octahedra. The corner-sharing octahedra tilt angles range from 55–63°. There are a spread of Mn–O bond distances ranging from 2.03–2.06 Å. In the second Mn2+ site, Mn2+ is bonded to six O2- atoms to form MnO6 octahedra that share a cornercorner with one NiO4 tetrahedra, corners with five MnO4 tetrahedra, edges with three MnO6 octahedra, and edges with three NiO6 octahedra. There are a spread of Mn–O bond distances ranging from 1.91–2.05 Å. In the third Mn2+ site, Mn2+ is bonded to six O2- atoms to form MnO6 octahedra that share corners with three equivalent MnO4 tetrahedra, corners with three equivalent NiO4 tetrahedra, edges with two NiO6 octahedra, and edges with four MnO6 octahedra. There are a spread of Mn–O bond distances ranging from 1.95–2.03 Å. In the fourth Mn2+ site, Mn2+ is bonded to four O2- atoms to form MnO4 tetrahedra that share corners with six MnO6 octahedra and corners with six NiO6 octahedra. The corner-sharing octahedra tilt angles range from 56–63°. There are a spread of Mn–O bond distances ranging from 2.03–2.06 Å. In the fifth Mn2+ site, Mn2+ is bonded to six O2- atoms to form MnO6 octahedra that share corners with two equivalent NiO4 tetrahedra, corners with four MnO4 tetrahedra, edges with three MnO6 octahedra, and edges with three NiO6 octahedra. There are a spread of Mn–O bond distances ranging from 1.89–2.12 Å. In the sixth Mn2+ site, Mn2+ is bonded to four O2- atoms to form MnO4 tetrahedra that share corners with three NiO6 octahedra and corners with nine MnO6 octahedra. The corner-sharing octahedra tilt angles range from 57–62°. There are one shorter (2.02 Å) and three longer (2.05 Å) Mn–O bond lengths. There are four inequivalent Ni4+ sites. In the first Ni4+ site, Ni4+ is bonded to four O2- atoms to form NiO4 tetrahedra that share corners with three NiO6 octahedra and corners with nine MnO6 octahedra. The corner-sharing octahedra tilt angles range from 53–63°. There are a spread of Ni–O bond distances ranging from 1.99–2.01 Å. In the second Ni4+ site, Ni4+ is bonded to six O2- atoms to form NiO6 octahedra that share a cornercorner with one NiO4 tetrahedra, corners with five MnO4 tetrahedra, an edgeedge with one NiO6 octahedra, and edges with five MnO6 octahedra. There are a spread of Ni–O bond distances ranging from 2.05–2.10 Å. In the third Ni4+ site, Ni4+ is bonded to six O2- atoms to form NiO6 octahedra that share corners with six MnO4 tetrahedra, edges with two NiO6 octahedra, and edges with four MnO6 octahedra. There are a spread of Ni–O bond distances ranging from 2.06–2.13 Å. In the fourth Ni4+ site, Ni4+ is bonded to six O2- atoms to form NiO6 octahedra that share corners with two equivalent NiO4 tetrahedra, corners with four MnO4 tetrahedra, an edgeedge with one NiO6 octahedra, and edges with five MnO6 octahedra. There are a spread of Ni–O bond distances ranging from 2.06–2.10 Å. There are twelve inequivalent O2- sites. In the first O2- site, O2- is bonded to two Mn2+ and two Ni4+ atoms to form distorted OMn2Ni2 trigonal pyramids that share corners with two equivalent OMn3Ni tetrahedra, corners with two OMn3Ni trigonal pyramids, and an edgeedge with one OMn2Ni2 trigonal pyramid. In the second O2- site, O2- is bonded in a rectangular see-saw-like geometry to three Mn2+ and one Ni4+ atom. In the third O2- site, O2- is bonded to three Mn2+ and one Ni4+ atom to form a mixture of distorted edge and corner-sharing OMn3Ni trigonal pyramids. In the fourth O2- site, O2- is bonded to three Mn2+ and one Ni4+ atom to form distorted corner-sharing OMn3Ni tetrahedra. In the fifth O2- site, O2- is bonded to four Mn2+ atoms to form a mixture of distorted edge and corner-sharing OMn4 trigonal pyramids. In the sixth O2- site, O2- is bonded in a distorted rectangular see-saw-like geometry to two Mn2+ and two Ni4+ atoms. In the seventh O2- site, O2- is bonded in a rectangular see-saw-like geometry to two equivalent Mn2+ and two Ni4+ atoms. In the eighth O2- site, O2- is bonded to three Mn2+ and one Ni4+ atom to form distorted OMn3Ni trigonal pyramids that share corners with two equivalent OMn2Ni2 trigonal pyramids and edges with three OMn3Ni trigonal pyramids. In the ninth O2- site, O2- is bonded in a rectangular see-saw-like geometry to three Mn2+ and one Ni4+ atom. In the tenth O2- site, O2- is bonded in a distorted rectangular see-saw-like geometry to two Mn2+ and two Ni4+ atoms. In the eleventh O2- site, O2- is bonded in a distorted rectangular see-saw-like geometry to three Mn2+ and one Ni4+ atom. In the twelfth O2- site, O2- is bonded in a rectangular see-saw-like geometry to three Mn2+ and one Ni4+ atom.