DOE OSTI2020
Ca4Mn2Al2O11 crystallizes in the monoclinic C2/m space group. The structure is three-dimensional. there are two inequivalent Ca2+ sites. In the first Ca2+ site, Ca2+ is bonded in a 9-coordinate geometry to nine O2- atoms. There are a spread of Ca–O bond distances ranging from 2.38–2.73 Å. In the second Ca2+ site, Ca2+ is bonded in a 7-coordinate geometry to eight O2- atoms. There are a spread of Ca–O bond distances ranging from 2.27–2.90 Å. Mn4+ is bonded to six O2- atoms to form MnO6 octahedra that share a cornercorner with one AlO6 octahedra, corners with four equivalent MnO6 octahedra, and a cornercorner with one AlO4 tetrahedra. The corner-sharing octahedra tilt angles range from 7–28°. There are a spread of Mn–O bond distances ranging from 1.82–2.18 Å. There are two inequivalent Al3+ sites. In the first Al3+ site, Al3+ is bonded to six O2- atoms to form AlO6 octahedra that share corners with two equivalent MnO6 octahedra and corners with four equivalent AlO6 octahedra. The corner-sharing octahedra tilt angles range from 12–22°. There are a spread of Al–O bond distances ranging from 1.91–1.96 Å. In the second Al3+ site, Al3+ is bonded to four O2- atoms to form AlO4 tetrahedra that share corners with two equivalent MnO6 octahedra and an edgeedge with one AlO4 tetrahedra. The corner-sharing octahedral tilt angles are 38°. There are a spread of Al–O bond distances ranging from 1.76–1.84 Å. There are nine inequivalent O2- sites. In the first O2- site, O2- is bonded in a 1-coordinate geometry to three equivalent Ca2+, one Mn4+, and one Al3+ atom. In the second O2- site, O2- is bonded in a 5-coordinate geometry to three equivalent Ca2+, one Mn4+, and one Al3+ atom. In the third O2- site, O2- is bonded in a 6-coordinate geometry to four equivalent Ca2+ and two equivalent Al3+ atoms. In the fourth O2- site, O2- is bonded in a 6-coordinate geometry to four equivalent Ca2+ and two equivalent Al3+ atoms. In the fifth O2- site, O2- is bonded in a 4-coordinate geometry to two equivalent Ca2+ and two equivalent Mn4+ atoms. In the sixth O2- site, O2- is bonded in a 4-coordinate geometry to two equivalent Ca2+ and two equivalent Mn4+ atoms. In the seventh O2- site, O2- is bonded to four Ca2+ and two equivalent Mn4+ atoms to form distorted OCa4Mn2 octahedra that share corners with two equivalent OCa2Al2 trigonal pyramids and faces with two equivalent OCa4Mn2 octahedra. In the eighth O2- site, O2- is bonded to four Ca2+ and two equivalent Mn4+ atoms to form distorted OCa4Mn2 octahedra that share corners with two equivalent OCa2Al2 trigonal pyramids and faces with two equivalent OCa4Mn2 octahedra. In the ninth O2- site, O2- is bonded to two equivalent Ca2+ and two equivalent Al3+ atoms to form OCa2Al2 trigonal pyramids that share corners with four OCa4Mn2 octahedra and an edgeedge with one OCa2Al2 trigonal pyramid. The corner-sharing octahedra tilt angles range from 23–49°.