DOE OSTI2020
MgEu2S4 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 S2- atoms to form MgS6 octahedra that share a cornercorner with one EuS6 octahedra, corners with two equivalent MgS6 octahedra, corners with four EuS7 pentagonal bipyramids, an edgeedge with one MgS6 octahedra, edges with four EuS6 octahedra, and edges with three EuS7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 10–54°. There are a spread of Mg–S bond distances ranging from 2.51–2.92 Å. In the second Mg2+ site, Mg2+ is bonded to six S2- atoms to form MgS6 octahedra that share a cornercorner with one EuS6 octahedra, corners with two equivalent MgS6 octahedra, corners with four EuS7 pentagonal bipyramids, an edgeedge with one MgS6 octahedra, edges with four EuS6 octahedra, and edges with three EuS7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 10–54°. There are a spread of Mg–S bond distances ranging from 2.50–2.82 Å. There are four inequivalent Eu3+ sites. In the first Eu3+ site, Eu3+ is bonded to six S2- atoms to form EuS6 octahedra that share a cornercorner with one MgS6 octahedra, corners with two equivalent EuS6 octahedra, corners with four EuS7 pentagonal bipyramids, an edgeedge with one EuS6 octahedra, edges with four MgS6 octahedra, and edges with three EuS7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 10–54°. There are a spread of Eu–S bond distances ranging from 2.74–2.83 Å. In the second Eu3+ site, Eu3+ is bonded to six S2- atoms to form EuS6 octahedra that share a cornercorner with one MgS6 octahedra, corners with two equivalent EuS6 octahedra, corners with four EuS7 pentagonal bipyramids, an edgeedge with one EuS6 octahedra, edges with four MgS6 octahedra, and edges with three EuS7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 10–54°. There are a spread of Eu–S bond distances ranging from 2.76–2.83 Å. In the third Eu3+ site, Eu3+ is bonded to seven S2- atoms to form distorted EuS7 pentagonal bipyramids that share corners with four MgS6 octahedra, corners with four EuS6 octahedra, edges with three MgS6 octahedra, edges with three EuS6 octahedra, and faces with two equivalent EuS7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 14–72°. There are a spread of Eu–S bond distances ranging from 2.82–3.08 Å. In the fourth Eu3+ site, Eu3+ is bonded to seven S2- atoms to form distorted EuS7 pentagonal bipyramids that share corners with four MgS6 octahedra, corners with four EuS6 octahedra, edges with three MgS6 octahedra, edges with three EuS6 octahedra, and faces with two equivalent EuS7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 15–73°. There are a spread of Eu–S bond distances ranging from 2.81–3.08 Å. There are eight inequivalent S2- sites. In the first S2- site, S2- is bonded to two Mg2+ and three Eu3+ atoms to form distorted SEu3Mg2 square pyramids that share corners with two equivalent SEu3Mg2 square pyramids, corners with three equivalent SEu3Mg tetrahedra, edges with five SEu3Mg2 square pyramids, and edges with two equivalent SEu4Mg trigonal bipyramids. In the second S2- site, S2- is bonded in a 5-coordinate geometry to two Mg2+ and three Eu3+ atoms. In the third S2- site, S2- is bonded to one Mg2+ and three Eu3+ atoms to form distorted SEu3Mg tetrahedra that share corners with seven SEu3Mg2 square pyramids, corners with three equivalent SEu4Mg trigonal bipyramids, and edges with three SEu3Mg2 square pyramids. In the fourth S2- site, S2- is bonded in a distorted rectangular see-saw-like geometry to one Mg2+ and three Eu3+ atoms. In the fifth S2- site, S2- is bonded to two Mg2+ and three Eu3+ atoms to form SEu3Mg2 square pyramids that share corners with two equivalent SEu3Mg2 square pyramids, a cornercorner with one SEu3Mg tetrahedra, corners with four equivalent SEu4Mg trigonal bipyramids, edges with five SEu3Mg2 square pyramids, and an edgeedge with one SEu3Mg tetrahedra. In the sixth S2- site, S2- is bonded to two Mg2+ and three Eu3+ atoms to form SEu3Mg2 square pyramids that share corners with two equivalent SEu4Mg square pyramids, a cornercorner with one SEu3Mg tetrahedra, corners with two equivalent SEu4Mg trigonal bipyramids, edges with five SEu3Mg2 square pyramids, an edgeedge with one SEu3Mg tetrahedra, and an edgeedge with one SEu4Mg trigonal bipyramid. In the seventh S2- site, S2- is bonded to one Mg2+ and four Eu3+ atoms to form distorted SEu4Mg square pyramids that share corners with two equivalent SEu3Mg2 square pyramids, corners with two equivalent SEu3Mg tetrahedra, corners with two equivalent SEu4Mg trigonal bipyramids, edges with five SEu3Mg2 square pyramids, an edgeedge with one SEu3Mg tetrahedra, and an edgeedge with one SEu4Mg trigonal bipyramid. In the eighth S2- site, S2- is bonded to one Mg2+ and four Eu3+ atoms to form distorted SEu4Mg trigonal bipyramids that share corners with eight SEu3Mg2 square pyramids, corners with three equivalent SEu3Mg tetrahedra, and edges with four SEu3Mg2 square pyramids.