DOE OSTI2020
MgLa2Se4 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 LaSe6 octahedra, corners with two equivalent MgSe6 octahedra, corners with four LaSe7 pentagonal bipyramids, an edgeedge with one MgSe6 octahedra, edges with four LaSe6 octahedra, and edges with three LaSe7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 10–53°. There are a spread of Mg–Se bond distances ranging from 2.66–3.17 Å. In the second Mg2+ site, Mg2+ is bonded to six Se2- atoms to form MgSe6 octahedra that share a cornercorner with one LaSe6 octahedra, corners with two equivalent MgSe6 octahedra, corners with four LaSe7 pentagonal bipyramids, an edgeedge with one MgSe6 octahedra, edges with four LaSe6 octahedra, and edges with three LaSe7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 10–53°. There are a spread of Mg–Se bond distances ranging from 2.66–3.04 Å. There are four inequivalent La3+ sites. In the first La3+ site, La3+ is bonded to six Se2- atoms to form LaSe6 octahedra that share a cornercorner with one MgSe6 octahedra, corners with two equivalent LaSe6 octahedra, corners with four LaSe7 pentagonal bipyramids, an edgeedge with one LaSe6 octahedra, edges with four MgSe6 octahedra, and edges with three LaSe7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 11–53°. There are a spread of La–Se bond distances ranging from 2.94–3.03 Å. In the second La3+ site, La3+ is bonded to six Se2- atoms to form LaSe6 octahedra that share a cornercorner with one MgSe6 octahedra, corners with two equivalent LaSe6 octahedra, corners with four LaSe7 pentagonal bipyramids, an edgeedge with one LaSe6 octahedra, edges with four MgSe6 octahedra, and edges with three LaSe7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 11–53°. There are a spread of La–Se bond distances ranging from 2.93–3.04 Å. In the third La3+ site, La3+ is bonded to seven Se2- atoms to form distorted LaSe7 pentagonal bipyramids that share corners with four MgSe6 octahedra, corners with four LaSe6 octahedra, edges with three MgSe6 octahedra, edges with three LaSe6 octahedra, and faces with two equivalent LaSe7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 14–72°. There are a spread of La–Se bond distances ranging from 2.99–3.29 Å. In the fourth La3+ site, La3+ is bonded to seven Se2- atoms to form distorted LaSe7 pentagonal bipyramids that share corners with four MgSe6 octahedra, corners with four LaSe6 octahedra, edges with three MgSe6 octahedra, edges with three LaSe6 octahedra, and faces with two equivalent LaSe7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 15–72°. There are a spread of La–Se bond distances ranging from 2.98–3.30 Å. There are eight inequivalent Se2- sites. In the first Se2- site, Se2- is bonded to two Mg2+ and three La3+ atoms to form distorted SeLa3Mg2 trigonal bipyramids that share corners with two equivalent SeLa3Mg2 square pyramids, corners with three equivalent SeLa3Mg tetrahedra, corners with two equivalent SeLa3Mg2 trigonal bipyramids, edges with five SeLa3Mg2 square pyramids, and edges with three SeLa3Mg2 trigonal bipyramids. In the second Se2- site, Se2- is bonded to two Mg2+ and three La3+ atoms to form distorted SeLa3Mg2 trigonal bipyramids that share corners with six SeLa3Mg2 square pyramids, corners with two equivalent SeLa3Mg tetrahedra, corners with two equivalent SeLa3Mg2 trigonal bipyramids, edges with three SeLa3Mg2 square pyramids, an edgeedge with one SeLa3Mg tetrahedra, and edges with three SeLa3Mg2 trigonal bipyramids. In the third Se2- site, Se2- is bonded to one Mg2+ and three La3+ atoms to form a mixture of distorted corner and edge-sharing SeLa3Mg tetrahedra. In the fourth Se2- site, Se2- is bonded in a distorted rectangular see-saw-like geometry to one Mg2+ and three La3+ atoms. In the fifth Se2- site, Se2- is bonded to two Mg2+ and three La3+ atoms to form distorted SeLa3Mg2 square pyramids that share a cornercorner with one SeLa3Mg tetrahedra, corners with eight SeLa3Mg2 trigonal bipyramids, edges with four SeLa3Mg2 square pyramids, an edgeedge with one SeLa3Mg tetrahedra, and edges with two SeLa3Mg2 trigonal bipyramids. In the sixth Se2- site, Se2- is bonded to two Mg2+ and three La3+ atoms to form distorted SeLa3Mg2 square pyramids that share corners with two equivalent SeLa4Mg square pyramids, a cornercorner with one SeLa3Mg tetrahedra, corners with six SeLa3Mg2 trigonal bipyramids, edges with three SeLa3Mg2 square pyramids, an edgeedge with one SeLa3Mg tetrahedra, and edges with three SeLa3Mg2 trigonal bipyramids. In the seventh Se2- site, Se2- is bonded to one Mg2+ and four La3+ atoms to form distorted SeLa4Mg square pyramids that share corners with two equivalent SeLa3Mg2 square pyramids, corners with two equivalent SeLa3Mg tetrahedra, corners with two equivalent SeLa4Mg trigonal bipyramids, edges with three SeLa3Mg2 square pyramids, an edgeedge with one SeLa3Mg tetrahedra, and edges with five SeLa3Mg2 trigonal bipyramids. In the eighth Se2- site, Se2- is bonded to one Mg2+ and four La3+ atoms to form distorted SeLa4Mg trigonal bipyramids that share corners with eight SeLa3Mg2 square pyramids, corners with three equivalent SeLa3Mg tetrahedra, edges with two SeLa3Mg2 square pyramids, and edges with four SeLa3Mg2 trigonal bipyramids.