DOI: 10.17188/1687154
title: Materials Data on Er2MgSe4 by Materials Project

description: MgEr2Se4 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 ErSe6 octahedra, corners with two equivalent MgSe6 octahedra, corners with four ErSe7 pentagonal bipyramids, an edgeedge with one MgSe6 octahedra, edges with four ErSe6 octahedra, and edges with three ErSe7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 13–54°. There are a spread of Mg–Se bond distances ranging from 2.66–2.96 Å. In the second Mg2+ site, Mg2+ is bonded to six Se2- atoms to form MgSe6 octahedra that share a cornercorner with one ErSe6 octahedra, corners with two equivalent MgSe6 octahedra, corners with four ErSe7 pentagonal bipyramids, an edgeedge with one MgSe6 octahedra, edges with four ErSe6 octahedra, and edges with three ErSe7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 13–54°. There are a spread of Mg–Se bond distances ranging from 2.70–2.87 Å. There are four inequivalent Er3+ sites. In the first Er3+ site, Er3+ is bonded to six Se2- atoms to form ErSe6 octahedra that share a cornercorner with one MgSe6 octahedra, corners with two equivalent ErSe6 octahedra, corners with four ErSe7 pentagonal bipyramids, an edgeedge with one ErSe6 octahedra, edges with four MgSe6 octahedra, and edges with three ErSe7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 12–54°. There are a spread of Er–Se bond distances ranging from 2.80–2.87 Å. In the second Er3+ site, Er3+ is bonded to six Se2- atoms to form ErSe6 octahedra that share a cornercorner with one MgSe6 octahedra, corners with two equivalent ErSe6 octahedra, corners with four ErSe7 pentagonal bipyramids, an edgeedge with one ErSe6 octahedra, edges with four MgSe6 octahedra, and edges with three ErSe7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 12–54°. There are a spread of Er–Se bond distances ranging from 2.79–2.90 Å. In the third Er3+ site, Er3+ is bonded to seven Se2- atoms to form distorted ErSe7 pentagonal bipyramids that share corners with four MgSe6 octahedra, corners with four ErSe6 octahedra, edges with three MgSe6 octahedra, edges with three ErSe6 octahedra, and faces with two equivalent ErSe7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 16–69°. There are a spread of Er–Se bond distances ranging from 2.84–3.13 Å. In the fourth Er3+ site, Er3+ is bonded to seven Se2- atoms to form distorted ErSe7 pentagonal bipyramids that share corners with four MgSe6 octahedra, corners with four ErSe6 octahedra, edges with three MgSe6 octahedra, edges with three ErSe6 octahedra, and faces with two equivalent ErSe7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 17–67°. There are a spread of Er–Se bond distances ranging from 2.83–3.15 Å. There are eight inequivalent Se2- sites. In the first Se2- site, Se2- is bonded to two Mg2+ and three Er3+ atoms to form distorted SeEr3Mg2 trigonal bipyramids that share corners with two equivalent SeEr3Mg2 square pyramids, corners with three equivalent SeEr3Mg tetrahedra, corners with two equivalent SeEr3Mg2 trigonal bipyramids, edges with five SeEr3Mg2 square pyramids, and edges with three SeEr3Mg2 trigonal bipyramids. In the second Se2- site, Se2- is bonded to two Mg2+ and three Er3+ atoms to form distorted SeEr3Mg2 trigonal bipyramids that share corners with six SeEr3Mg2 square pyramids, corners with two equivalent SeEr3Mg tetrahedra, corners with two equivalent SeEr3Mg2 trigonal bipyramids, edges with three SeEr3Mg2 square pyramids, an edgeedge with one SeEr3Mg tetrahedra, and edges with three SeEr3Mg2 trigonal bipyramids. In the third Se2- site, Se2- is bonded to one Mg2+ and three Er3+ atoms to form a mixture of distorted edge and corner-sharing SeEr3Mg tetrahedra. In the fourth Se2- site, Se2- is bonded in a distorted rectangular see-saw-like geometry to one Mg2+ and three Er3+ atoms. In the fifth Se2- site, Se2- is bonded to two Mg2+ and three Er3+ atoms to form distorted SeEr3Mg2 square pyramids that share a cornercorner with one SeEr3Mg tetrahedra, corners with eight SeEr3Mg2 trigonal bipyramids, edges with four SeEr3Mg2 square pyramids, an edgeedge with one SeEr3Mg tetrahedra, and edges with two SeEr3Mg2 trigonal bipyramids. In the sixth Se2- site, Se2- is bonded to two Mg2+ and three Er3+ atoms to form distorted SeEr3Mg2 square pyramids that share corners with two equivalent SeEr4Mg square pyramids, a cornercorner with one SeEr3Mg tetrahedra, corners with six SeEr3Mg2 trigonal bipyramids, edges with three SeEr3Mg2 square pyramids, an edgeedge with one SeEr3Mg tetrahedra, and edges with three SeEr3Mg2 trigonal bipyramids. In the seventh Se2- site, Se2- is bonded to one Mg2+ and four Er3+ atoms to form distorted SeEr4Mg square pyramids that share corners with two equivalent SeEr3Mg2 square pyramids, corners with two equivalent SeEr3Mg tetrahedra, corners with two equivalent SeEr4Mg trigonal bipyramids, edges with three SeEr3Mg2 square pyramids, an edgeedge with one SeEr3Mg tetrahedra, and edges with five SeEr3Mg2 trigonal bipyramids. In the eighth Se2- site, Se2- is bonded to one Mg2+ and four Er3+ atoms to form distorted SeEr4Mg trigonal bipyramids that share corners with eight SeEr3Mg2 square pyramids, corners with three equivalent SeEr3Mg tetrahedra, edges with two SeEr3Mg2 square pyramids, and edges with four SeEr3Mg2 trigonal bipyramids.