DOE OSTI2020
MgHo2Se4 crystallizes in the orthorhombic Pca2_1 space group. The structure is three-dimensional. there are two inequivalent Mg2+ sites. In the first Mg2+ site, Mg2+ is bonded to six Se2- atoms to form MgSe6 octahedra that share a cornercorner with one HoSe6 octahedra, corners with two equivalent MgSe6 octahedra, corners with four HoSe7 pentagonal bipyramids, an edgeedge with one MgSe6 octahedra, edges with four HoSe6 octahedra, and edges with three HoSe7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 14–53°. There are a spread of Mg–Se bond distances ranging from 2.67–2.94 Å. In the second Mg2+ site, Mg2+ is bonded to six Se2- atoms to form MgSe6 octahedra that share a cornercorner with one HoSe6 octahedra, corners with two equivalent MgSe6 octahedra, corners with four HoSe7 pentagonal bipyramids, an edgeedge with one MgSe6 octahedra, edges with four HoSe6 octahedra, and edges with three HoSe7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 14–54°. There are a spread of Mg–Se bond distances ranging from 2.70–2.85 Å. There are four inequivalent Ho3+ sites. In the first Ho3+ site, Ho3+ is bonded to six Se2- atoms to form HoSe6 octahedra that share a cornercorner with one MgSe6 octahedra, corners with two equivalent HoSe6 octahedra, corners with four HoSe7 pentagonal bipyramids, an edgeedge with one HoSe6 octahedra, edges with four MgSe6 octahedra, and edges with three HoSe7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 13–54°. There are a spread of Ho–Se bond distances ranging from 2.81–2.87 Å. In the second Ho3+ site, Ho3+ is bonded to six Se2- atoms to form HoSe6 octahedra that share a cornercorner with one MgSe6 octahedra, corners with two equivalent HoSe6 octahedra, corners with four HoSe7 pentagonal bipyramids, an edgeedge with one HoSe6 octahedra, edges with four MgSe6 octahedra, and edges with three HoSe7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 13–53°. There are a spread of Ho–Se bond distances ranging from 2.79–2.90 Å. In the third Ho3+ site, Ho3+ is bonded to seven Se2- atoms to form distorted HoSe7 pentagonal bipyramids that share corners with four MgSe6 octahedra, corners with four HoSe6 octahedra, edges with three MgSe6 octahedra, edges with three HoSe6 octahedra, and faces with two equivalent HoSe7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 16–68°. There are a spread of Ho–Se bond distances ranging from 2.85–3.12 Å. In the fourth Ho3+ site, Ho3+ is bonded to seven Se2- atoms to form distorted HoSe7 pentagonal bipyramids that share corners with four MgSe6 octahedra, corners with four HoSe6 octahedra, edges with three MgSe6 octahedra, edges with three HoSe6 octahedra, and faces with two equivalent HoSe7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 17–67°. There are a spread of Ho–Se bond distances ranging from 2.84–3.14 Å. There are eight inequivalent Se2- sites. In the first Se2- site, Se2- is bonded to two Mg2+ and three Ho3+ atoms to form distorted SeHo3Mg2 trigonal bipyramids that share corners with two equivalent SeHo3Mg2 square pyramids, corners with three equivalent SeHo3Mg tetrahedra, corners with two equivalent SeHo3Mg2 trigonal bipyramids, edges with five SeHo3Mg2 square pyramids, and edges with three SeHo3Mg2 trigonal bipyramids. In the second Se2- site, Se2- is bonded to two Mg2+ and three Ho3+ atoms to form distorted SeHo3Mg2 trigonal bipyramids that share corners with six SeHo3Mg2 square pyramids, corners with two equivalent SeHo3Mg tetrahedra, corners with two equivalent SeHo3Mg2 trigonal bipyramids, edges with three SeHo3Mg2 square pyramids, an edgeedge with one SeHo3Mg tetrahedra, and edges with three SeHo3Mg2 trigonal bipyramids. In the third Se2- site, Se2- is bonded to one Mg2+ and three Ho3+ atoms to form a mixture of distorted edge and corner-sharing SeHo3Mg tetrahedra. In the fourth Se2- site, Se2- is bonded in a distorted rectangular see-saw-like geometry to one Mg2+ and three Ho3+ atoms. In the fifth Se2- site, Se2- is bonded to two Mg2+ and three Ho3+ atoms to form distorted SeHo3Mg2 square pyramids that share a cornercorner with one SeHo3Mg tetrahedra, corners with eight SeHo3Mg2 trigonal bipyramids, edges with four SeHo3Mg2 square pyramids, an edgeedge with one SeHo3Mg tetrahedra, and edges with two SeHo3Mg2 trigonal bipyramids. In the sixth Se2- site, Se2- is bonded to two Mg2+ and three Ho3+ atoms to form distorted SeHo3Mg2 square pyramids that share corners with two equivalent SeHo4Mg square pyramids, a cornercorner with one SeHo3Mg tetrahedra, corners with six SeHo3Mg2 trigonal bipyramids, edges with three SeHo3Mg2 square pyramids, an edgeedge with one SeHo3Mg tetrahedra, and edges with three SeHo3Mg2 trigonal bipyramids. In the seventh Se2- site, Se2- is bonded to one Mg2+ and four Ho3+ atoms to form distorted SeHo4Mg square pyramids that share corners with two equivalent SeHo3Mg2 square pyramids, corners with two equivalent SeHo3Mg tetrahedra, corners with two equivalent SeHo4Mg trigonal bipyramids, edges with three SeHo3Mg2 square pyramids, an edgeedge with one SeHo3Mg tetrahedra, and edges with five SeHo3Mg2 trigonal bipyramids. In the eighth Se2- site, Se2- is bonded to one Mg2+ and four Ho3+ atoms to form distorted SeHo4Mg trigonal bipyramids that share corners with eight SeHo3Mg2 square pyramids, corners with three equivalent SeHo3Mg tetrahedra, edges with two SeHo3Mg2 square pyramids, and edges with four SeHo3Mg2 trigonal bipyramids.