DOE OSTI2020
MgLa2S4 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 LaS6 octahedra, corners with two equivalent MgS6 octahedra, corners with four LaS7 pentagonal bipyramids, an edgeedge with one MgS6 octahedra, edges with four LaS6 octahedra, and edges with three LaS7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 10–54°. There are a spread of Mg–S bond distances ranging from 2.54–3.05 Å. In the second Mg2+ site, Mg2+ is bonded to six S2- atoms to form MgS6 octahedra that share a cornercorner with one LaS6 octahedra, corners with two equivalent MgS6 octahedra, corners with four LaS7 pentagonal bipyramids, an edgeedge with one MgS6 octahedra, edges with four LaS6 octahedra, and edges with three LaS7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 10–54°. There are a spread of Mg–S bond distances ranging from 2.54–2.92 Å. There are four inequivalent La3+ sites. In the first La3+ site, La3+ is bonded to six S2- atoms to form LaS6 octahedra that share a cornercorner with one MgS6 octahedra, corners with two equivalent LaS6 octahedra, corners with four LaS7 pentagonal bipyramids, an edgeedge with one LaS6 octahedra, edges with four MgS6 octahedra, and edges with three LaS7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 11–54°. There are a spread of La–S bond distances ranging from 2.82–2.92 Å. In the second La3+ site, La3+ is bonded to six S2- atoms to form LaS6 octahedra that share a cornercorner with one MgS6 octahedra, corners with two equivalent LaS6 octahedra, corners with four LaS7 pentagonal bipyramids, an edgeedge with one LaS6 octahedra, edges with four MgS6 octahedra, and edges with three LaS7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 11–54°. There are a spread of La–S bond distances ranging from 2.81–2.90 Å. In the third La3+ site, La3+ is bonded to seven S2- atoms to form distorted LaS7 pentagonal bipyramids that share corners with four MgS6 octahedra, corners with four LaS6 octahedra, edges with three MgS6 octahedra, edges with three LaS6 octahedra, and faces with two equivalent LaS7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 14–72°. There are a spread of La–S bond distances ranging from 2.87–3.16 Å. In the fourth La3+ site, La3+ is bonded to seven S2- atoms to form distorted LaS7 pentagonal bipyramids that share corners with four MgS6 octahedra, corners with four LaS6 octahedra, edges with three MgS6 octahedra, edges with three LaS6 octahedra, and faces with two equivalent LaS7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 16–72°. There are a spread of La–S bond distances ranging from 2.86–3.17 Å. There are eight inequivalent S2- sites. In the first S2- site, S2- is bonded to two Mg2+ and three La3+ atoms to form distorted SLa3Mg2 trigonal bipyramids that share corners with two equivalent SLa3Mg2 square pyramids, corners with three equivalent SLa3Mg tetrahedra, edges with five SLa3Mg2 square pyramids, and edges with two equivalent SLa4Mg trigonal bipyramids. In the second S2- site, S2- is bonded in a 5-coordinate geometry to two Mg2+ and three La3+ atoms. In the third S2- site, S2- is bonded to one Mg2+ and three La3+ atoms to form a mixture of distorted edge and corner-sharing SLa3Mg tetrahedra. In the fourth S2- site, S2- is bonded in a distorted rectangular see-saw-like geometry to one Mg2+ and three La3+ atoms. In the fifth S2- site, S2- is bonded to two Mg2+ and three La3+ atoms to form distorted SLa3Mg2 square pyramids that share a cornercorner with one SLa3Mg tetrahedra, corners with six SLa3Mg2 trigonal bipyramids, edges with four SLa3Mg2 square pyramids, an edgeedge with one SLa3Mg tetrahedra, and an edgeedge with one SLa3Mg2 trigonal bipyramid. In the sixth S2- site, S2- is bonded to two Mg2+ and three La3+ atoms to form distorted SLa3Mg2 square pyramids that share corners with two equivalent SLa4Mg square pyramids, a cornercorner with one SLa3Mg tetrahedra, corners with two equivalent SLa4Mg trigonal bipyramids, edges with three SLa3Mg2 square pyramids, an edgeedge with one SLa3Mg tetrahedra, and edges with three SLa3Mg2 trigonal bipyramids. In the seventh S2- site, S2- is bonded to one Mg2+ and four La3+ atoms to form distorted SLa4Mg square pyramids that share corners with two equivalent SLa3Mg2 square pyramids, corners with two equivalent SLa3Mg tetrahedra, corners with two equivalent SLa4Mg trigonal bipyramids, edges with three SLa3Mg2 square pyramids, an edgeedge with one SLa3Mg tetrahedra, and edges with three SLa3Mg2 trigonal bipyramids. In the eighth S2- site, S2- is bonded to one Mg2+ and four La3+ atoms to form distorted SLa4Mg trigonal bipyramids that share corners with eight SLa3Mg2 square pyramids, corners with three equivalent SLa3Mg tetrahedra, edges with two SLa3Mg2 square pyramids, and edges with two equivalent SLa3Mg2 trigonal bipyramids.