DOE OSTI2020
MgDy2Se4 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 DySe6 octahedra, corners with two equivalent MgSe6 octahedra, corners with four DySe7 pentagonal bipyramids, an edgeedge with one MgSe6 octahedra, edges with four DySe6 octahedra, and edges with three DySe7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 14–54°. There are a spread of Mg–Se bond distances ranging from 2.67–2.93 Å. In the second Mg2+ site, Mg2+ is bonded to six Se2- atoms to form MgSe6 octahedra that share a cornercorner with one DySe6 octahedra, corners with two equivalent MgSe6 octahedra, corners with four DySe7 pentagonal bipyramids, an edgeedge with one MgSe6 octahedra, edges with four DySe6 octahedra, and edges with three DySe7 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 Dy3+ sites. In the first Dy3+ site, Dy3+ is bonded to six Se2- atoms to form DySe6 octahedra that share a cornercorner with one MgSe6 octahedra, corners with two equivalent DySe6 octahedra, corners with four DySe7 pentagonal bipyramids, an edgeedge with one DySe6 octahedra, edges with four MgSe6 octahedra, and edges with three DySe7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 13–54°. There are a spread of Dy–Se bond distances ranging from 2.82–2.88 Å. In the second Dy3+ site, Dy3+ is bonded to six Se2- atoms to form DySe6 octahedra that share a cornercorner with one MgSe6 octahedra, corners with two equivalent DySe6 octahedra, corners with four DySe7 pentagonal bipyramids, an edgeedge with one DySe6 octahedra, edges with four MgSe6 octahedra, and edges with three DySe7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 13–54°. There are a spread of Dy–Se bond distances ranging from 2.80–2.91 Å. In the third Dy3+ site, Dy3+ is bonded to seven Se2- atoms to form distorted DySe7 pentagonal bipyramids that share corners with four MgSe6 octahedra, corners with four DySe6 octahedra, edges with three MgSe6 octahedra, edges with three DySe6 octahedra, and faces with two equivalent DySe7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 16–68°. There are a spread of Dy–Se bond distances ranging from 2.86–3.13 Å. In the fourth Dy3+ site, Dy3+ is bonded to seven Se2- atoms to form distorted DySe7 pentagonal bipyramids that share corners with four MgSe6 octahedra, corners with four DySe6 octahedra, edges with three MgSe6 octahedra, edges with three DySe6 octahedra, and faces with two equivalent DySe7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 17–67°. There are a spread of Dy–Se bond distances ranging from 2.85–3.15 Å. There are eight inequivalent Se2- sites. In the first Se2- site, Se2- is bonded to two Mg2+ and three Dy3+ atoms to form distorted SeDy3Mg2 trigonal bipyramids that share corners with two equivalent SeDy3Mg2 square pyramids, corners with three equivalent SeDy3Mg tetrahedra, corners with two equivalent SeDy3Mg2 trigonal bipyramids, edges with five SeDy3Mg2 square pyramids, and edges with three SeDy3Mg2 trigonal bipyramids. In the second Se2- site, Se2- is bonded to two Mg2+ and three Dy3+ atoms to form distorted SeDy3Mg2 trigonal bipyramids that share corners with six SeDy3Mg2 square pyramids, corners with two equivalent SeDy3Mg tetrahedra, corners with two equivalent SeDy3Mg2 trigonal bipyramids, edges with three SeDy3Mg2 square pyramids, an edgeedge with one SeDy3Mg tetrahedra, and edges with three SeDy3Mg2 trigonal bipyramids. In the third Se2- site, Se2- is bonded to one Mg2+ and three Dy3+ atoms to form a mixture of distorted corner and edge-sharing SeDy3Mg tetrahedra. In the fourth Se2- site, Se2- is bonded in a distorted rectangular see-saw-like geometry to one Mg2+ and three Dy3+ atoms. In the fifth Se2- site, Se2- is bonded to two Mg2+ and three Dy3+ atoms to form distorted SeDy3Mg2 square pyramids that share a cornercorner with one SeDy3Mg tetrahedra, corners with eight SeDy3Mg2 trigonal bipyramids, edges with four SeDy3Mg2 square pyramids, an edgeedge with one SeDy3Mg tetrahedra, and edges with two SeDy3Mg2 trigonal bipyramids. In the sixth Se2- site, Se2- is bonded to two Mg2+ and three Dy3+ atoms to form distorted SeDy3Mg2 square pyramids that share corners with two equivalent SeDy4Mg square pyramids, a cornercorner with one SeDy3Mg tetrahedra, corners with six SeDy3Mg2 trigonal bipyramids, edges with three SeDy3Mg2 square pyramids, an edgeedge with one SeDy3Mg tetrahedra, and edges with three SeDy3Mg2 trigonal bipyramids. In the seventh Se2- site, Se2- is bonded to one Mg2+ and four Dy3+ atoms to form distorted SeDy4Mg square pyramids that share corners with two equivalent SeDy3Mg2 square pyramids, corners with two equivalent SeDy3Mg tetrahedra, corners with two equivalent SeDy4Mg trigonal bipyramids, edges with three SeDy3Mg2 square pyramids, an edgeedge with one SeDy3Mg tetrahedra, and edges with five SeDy3Mg2 trigonal bipyramids. In the eighth Se2- site, Se2- is bonded to one Mg2+ and four Dy3+ atoms to form distorted SeDy4Mg trigonal bipyramids that share corners with eight SeDy3Mg2 square pyramids, corners with three equivalent SeDy3Mg tetrahedra, edges with two SeDy3Mg2 square pyramids, and edges with four SeDy3Mg2 trigonal bipyramids.