DOE OSTI2020
Mg2Mn3O8 crystallizes in the orthorhombic Pmn2_1 space group. The structure is three-dimensional. there are two inequivalent Mg2+ sites. In the first Mg2+ site, Mg2+ is bonded to six O2- atoms to form MgO6 octahedra that share corners with seven MnO6 octahedra, corners with two equivalent MgO4 tetrahedra, and edges with three MnO6 octahedra. The corner-sharing octahedra tilt angles range from 15–56°. There are a spread of Mg–O bond distances ranging from 2.06–2.28 Å. In the second Mg2+ site, Mg2+ is bonded to four O2- atoms to form MgO4 tetrahedra that share corners with two equivalent MgO6 octahedra and corners with nine MnO6 octahedra. The corner-sharing octahedra tilt angles range from 58–63°. There are a spread of Mg–O bond distances ranging from 1.97–2.01 Å. There are two inequivalent Mn4+ sites. In the first Mn4+ site, Mn4+ is bonded to six O2- atoms to form MnO6 octahedra that share corners with three equivalent MgO6 octahedra, corners with three equivalent MgO4 tetrahedra, an edgeedge with one MgO6 octahedra, and edges with four equivalent MnO6 octahedra. The corner-sharing octahedra tilt angles range from 15–49°. There are a spread of Mn–O bond distances ranging from 1.91–1.96 Å. In the second Mn4+ site, Mn4+ is bonded to six O2- atoms to form MnO6 octahedra that share corners with two equivalent MgO6 octahedra, corners with three equivalent MgO4 tetrahedra, an edgeedge with one MgO6 octahedra, and edges with four MnO6 octahedra. The corner-sharing octahedra tilt angles range from 53–56°. There are a spread of Mn–O bond distances ranging from 1.89–2.02 Å. There are six inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted trigonal planar geometry to one Mg2+ and two equivalent Mn4+ atoms. In the second O2- site, O2- is bonded to one Mg2+ and three Mn4+ atoms to form a mixture of distorted edge and corner-sharing OMgMn3 trigonal pyramids. In the third O2- site, O2- is bonded in a distorted rectangular see-saw-like geometry to one Mg2+ and three Mn4+ atoms. In the fourth O2- site, O2- is bonded in a distorted trigonal planar geometry to one Mg2+ and two equivalent Mn4+ atoms. In the fifth O2- site, O2- is bonded to two Mg2+ and two Mn4+ atoms to form distorted OMg2Mn2 tetrahedra that share a cornercorner with one OMg2Mn2 tetrahedra, a cornercorner with one OMgMn3 trigonal pyramid, an edgeedge with one OMg2Mn2 tetrahedra, and an edgeedge with one OMgMn3 trigonal pyramid. In the sixth O2- site, O2- is bonded in a distorted trigonal planar geometry to one Mg2+ and two Mn4+ atoms.