DOE OSTI2020
MgCe2S4 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 CeS6 octahedra, corners with two equivalent MgS6 octahedra, corners with four CeS7 pentagonal bipyramids, an edgeedge with one MgS6 octahedra, edges with four CeS6 octahedra, and edges with three CeS7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 10–54°. There are a spread of Mg–S bond distances ranging from 2.52–2.87 Å. In the second Mg2+ site, Mg2+ is bonded to six S2- atoms to form MgS6 octahedra that share a cornercorner with one CeS6 octahedra, corners with two equivalent MgS6 octahedra, corners with four CeS7 pentagonal bipyramids, an edgeedge with one MgS6 octahedra, edges with four CeS6 octahedra, and edges with three CeS7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 10–54°. There are a spread of Mg–S bond distances ranging from 2.54–2.77 Å. There are four inequivalent Ce3+ sites. In the first Ce3+ site, Ce3+ is bonded to six S2- atoms to form CeS6 octahedra that share a cornercorner with one MgS6 octahedra, corners with two equivalent CeS6 octahedra, corners with four CeS7 pentagonal bipyramids, an edgeedge with one CeS6 octahedra, edges with four MgS6 octahedra, and edges with three CeS7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 10–54°. There are a spread of Ce–S bond distances ranging from 2.75–2.81 Å. In the second Ce3+ site, Ce3+ is bonded to six S2- atoms to form CeS6 octahedra that share a cornercorner with one MgS6 octahedra, corners with two equivalent CeS6 octahedra, corners with four CeS7 pentagonal bipyramids, an edgeedge with one CeS6 octahedra, edges with four MgS6 octahedra, and edges with three CeS7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 10–54°. There are a spread of Ce–S bond distances ranging from 2.74–2.83 Å. In the third Ce3+ site, Ce3+ is bonded to seven S2- atoms to form distorted CeS7 pentagonal bipyramids that share corners with four MgS6 octahedra, corners with four CeS6 octahedra, edges with three MgS6 octahedra, edges with three CeS6 octahedra, and faces with two equivalent CeS7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 15–71°. There are a spread of Ce–S bond distances ranging from 2.81–3.10 Å. In the fourth Ce3+ site, Ce3+ is bonded to seven S2- atoms to form distorted CeS7 pentagonal bipyramids that share corners with four MgS6 octahedra, corners with four CeS6 octahedra, edges with three MgS6 octahedra, edges with three CeS6 octahedra, and faces with two equivalent CeS7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 17–70°. There are a spread of Ce–S bond distances ranging from 2.81–3.12 Å. There are eight inequivalent S2- sites. In the first S2- site, S2- is bonded to two Mg2+ and three Ce3+ atoms to form distorted SCe3Mg2 trigonal bipyramids that share corners with two equivalent SCe3Mg2 square pyramids, corners with three equivalent SCe3Mg tetrahedra, corners with two equivalent SCe3Mg2 trigonal bipyramids, edges with five SCe3Mg2 square pyramids, and edges with three SCe3Mg2 trigonal bipyramids. In the second S2- site, S2- is bonded to two Mg2+ and three Ce3+ atoms to form distorted SCe3Mg2 trigonal bipyramids that share corners with six SCe3Mg2 square pyramids, corners with two equivalent SCe3Mg tetrahedra, corners with two equivalent SCe3Mg2 trigonal bipyramids, edges with three SCe3Mg2 square pyramids, an edgeedge with one SCe3Mg tetrahedra, and edges with three SCe3Mg2 trigonal bipyramids. In the third S2- site, S2- is bonded to one Mg2+ and three Ce3+ atoms to form a mixture of distorted edge and corner-sharing SCe3Mg tetrahedra. In the fourth S2- site, S2- is bonded in a distorted rectangular see-saw-like geometry to one Mg2+ and three Ce3+ atoms. In the fifth S2- site, S2- is bonded to two Mg2+ and three Ce3+ atoms to form distorted SCe3Mg2 square pyramids that share a cornercorner with one SCe3Mg tetrahedra, corners with eight SCe3Mg2 trigonal bipyramids, edges with four SCe3Mg2 square pyramids, an edgeedge with one SCe3Mg tetrahedra, and edges with two SCe3Mg2 trigonal bipyramids. In the sixth S2- site, S2- is bonded to two Mg2+ and three Ce3+ atoms to form SCe3Mg2 square pyramids that share corners with two equivalent SCe4Mg square pyramids, a cornercorner with one SCe3Mg tetrahedra, corners with six SCe3Mg2 trigonal bipyramids, edges with three SCe3Mg2 square pyramids, an edgeedge with one SCe3Mg tetrahedra, and edges with three SCe3Mg2 trigonal bipyramids. In the seventh S2- site, S2- is bonded to one Mg2+ and four Ce3+ atoms to form distorted SCe4Mg square pyramids that share corners with two equivalent SCe3Mg2 square pyramids, corners with two equivalent SCe3Mg tetrahedra, corners with two equivalent SCe4Mg trigonal bipyramids, edges with three SCe3Mg2 square pyramids, an edgeedge with one SCe3Mg tetrahedra, and edges with five SCe3Mg2 trigonal bipyramids. In the eighth S2- site, S2- is bonded to one Mg2+ and four Ce3+ atoms to form distorted SCe4Mg trigonal bipyramids that share corners with eight SCe3Mg2 square pyramids, corners with three equivalent SCe3Mg tetrahedra, edges with two SCe3Mg2 square pyramids, and edges with four SCe3Mg2 trigonal bipyramids.