DOE OSTI2020
MgGd2S4 crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. Mg2+ is bonded to five S2- atoms to form MgS5 square pyramids that share corners with four GdS6 octahedra, edges with four GdS6 octahedra, and edges with four equivalent MgS5 square pyramids. The corner-sharing octahedral tilt angles are 5°. There are a spread of Mg–S bond distances ranging from 2.54–2.64 Å. There are two inequivalent Gd3+ sites. In the first Gd3+ site, Gd3+ is bonded to six S2- atoms to form GdS6 octahedra that share corners with three equivalent GdS6 octahedra, corners with two equivalent MgS5 square pyramids, edges with six GdS6 octahedra, and an edgeedge with one MgS5 square pyramid. The corner-sharing octahedra tilt angles range from 54–59°. There are a spread of Gd–S bond distances ranging from 2.72–2.84 Å. In the second Gd3+ site, Gd3+ is bonded to six S2- atoms to form GdS6 octahedra that share corners with three equivalent GdS6 octahedra, corners with two equivalent MgS5 square pyramids, edges with four GdS6 octahedra, and edges with three equivalent MgS5 square pyramids. The corner-sharing octahedra tilt angles range from 54–59°. There are a spread of Gd–S bond distances ranging from 2.66–2.88 Å. There are four inequivalent S2- sites. In the first S2- site, S2- is bonded to three equivalent Mg2+ and two equivalent Gd3+ atoms to form a mixture of edge and corner-sharing SGd2Mg3 square pyramids. In the second S2- site, S2- is bonded in a rectangular see-saw-like geometry to four Gd3+ atoms. In the third S2- site, S2- is bonded in a 3-coordinate geometry to three Gd3+ atoms. In the fourth S2- site, S2- is bonded to two equivalent Mg2+ and three Gd3+ atoms to form SGd3Mg2 square pyramids that share corners with two equivalent SGd2Mg3 square pyramids and edges with five SGd3Mg2 square pyramids.