DOE OSTI2020
MgY2Se4 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 YSe6 octahedra, corners with two equivalent MgSe6 octahedra, corners with four YSe7 pentagonal bipyramids, an edgeedge with one MgSe6 octahedra, edges with four YSe6 octahedra, and edges with three YSe7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 13–54°. 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 YSe6 octahedra, corners with two equivalent MgSe6 octahedra, corners with four YSe7 pentagonal bipyramids, an edgeedge with one MgSe6 octahedra, edges with four YSe6 octahedra, and edges with three YSe7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 13–54°. There are a spread of Mg–Se bond distances ranging from 2.70–2.86 Å. There are four inequivalent Y3+ sites. In the first Y3+ site, Y3+ is bonded to six Se2- atoms to form YSe6 octahedra that share a cornercorner with one MgSe6 octahedra, corners with two equivalent YSe6 octahedra, corners with four YSe7 pentagonal bipyramids, an edgeedge with one YSe6 octahedra, edges with four MgSe6 octahedra, and edges with three YSe7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 13–54°. There are a spread of Y–Se bond distances ranging from 2.81–2.88 Å. In the second Y3+ site, Y3+ is bonded to six Se2- atoms to form YSe6 octahedra that share a cornercorner with one MgSe6 octahedra, corners with two equivalent YSe6 octahedra, corners with four YSe7 pentagonal bipyramids, an edgeedge with one YSe6 octahedra, edges with four MgSe6 octahedra, and edges with three YSe7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 13–54°. There are a spread of Y–Se bond distances ranging from 2.81–2.92 Å. In the third Y3+ site, Y3+ is bonded to seven Se2- atoms to form distorted YSe7 pentagonal bipyramids that share corners with four MgSe6 octahedra, corners with four YSe6 octahedra, edges with three MgSe6 octahedra, edges with three YSe6 octahedra, and faces with two equivalent YSe7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 15–68°. There are a spread of Y–Se bond distances ranging from 2.86–3.12 Å. In the fourth Y3+ site, Y3+ is bonded to seven Se2- atoms to form distorted YSe7 pentagonal bipyramids that share corners with four MgSe6 octahedra, corners with four YSe6 octahedra, edges with three MgSe6 octahedra, edges with three YSe6 octahedra, and faces with two equivalent YSe7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 17–68°. There are a spread of Y–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 Y3+ atoms to form distorted SeY3Mg2 trigonal bipyramids that share corners with two equivalent SeY3Mg2 square pyramids, corners with three equivalent SeY3Mg tetrahedra, corners with two equivalent SeY3Mg2 trigonal bipyramids, edges with five SeY3Mg2 square pyramids, and edges with three SeY3Mg2 trigonal bipyramids. In the second Se2- site, Se2- is bonded to two Mg2+ and three Y3+ atoms to form distorted SeY3Mg2 trigonal bipyramids that share corners with six SeY3Mg2 square pyramids, corners with two equivalent SeY3Mg tetrahedra, corners with two equivalent SeY3Mg2 trigonal bipyramids, edges with three SeY3Mg2 square pyramids, an edgeedge with one SeY3Mg tetrahedra, and edges with three SeY3Mg2 trigonal bipyramids. In the third Se2- site, Se2- is bonded to one Mg2+ and three Y3+ atoms to form a mixture of distorted edge and corner-sharing SeY3Mg tetrahedra. In the fourth Se2- site, Se2- is bonded in a distorted rectangular see-saw-like geometry to one Mg2+ and three Y3+ atoms. In the fifth Se2- site, Se2- is bonded to two Mg2+ and three Y3+ atoms to form distorted SeY3Mg2 square pyramids that share a cornercorner with one SeY3Mg tetrahedra, corners with eight SeY3Mg2 trigonal bipyramids, edges with four SeY3Mg2 square pyramids, an edgeedge with one SeY3Mg tetrahedra, and edges with two SeY3Mg2 trigonal bipyramids. In the sixth Se2- site, Se2- is bonded to two Mg2+ and three Y3+ atoms to form SeY3Mg2 square pyramids that share corners with two equivalent SeY4Mg square pyramids, a cornercorner with one SeY3Mg tetrahedra, corners with six SeY3Mg2 trigonal bipyramids, edges with three SeY3Mg2 square pyramids, an edgeedge with one SeY3Mg tetrahedra, and edges with three SeY3Mg2 trigonal bipyramids. In the seventh Se2- site, Se2- is bonded to one Mg2+ and four Y3+ atoms to form distorted SeY4Mg square pyramids that share corners with two equivalent SeY3Mg2 square pyramids, corners with two equivalent SeY3Mg tetrahedra, corners with two equivalent SeY4Mg trigonal bipyramids, edges with three SeY3Mg2 square pyramids, an edgeedge with one SeY3Mg tetrahedra, and edges with five SeY3Mg2 trigonal bipyramids. In the eighth Se2- site, Se2- is bonded to one Mg2+ and four Y3+ atoms to form distorted SeY4Mg trigonal bipyramids that share corners with eight SeY3Mg2 square pyramids, corners with three equivalent SeY3Mg tetrahedra, edges with two SeY3Mg2 square pyramids, and edges with four SeY3Mg2 trigonal bipyramids.