DOE OSTI2020
BaCuS2 crystallizes in the tetragonal P4/nmm space group. The structure is three-dimensional. Ba2+ is bonded to nine S2- atoms to form distorted BaS9 square pyramids that share corners with four equivalent BaS9 square pyramids, corners with five equivalent CuS5 trigonal bipyramids, edges with eight equivalent BaS9 square pyramids, faces with four equivalent BaS9 square pyramids, and faces with five equivalent CuS5 trigonal bipyramids. There are a spread of Ba–S bond distances ranging from 3.18–3.59 Å. Cu2+ is bonded to five S2- atoms to form distorted CuS5 trigonal bipyramids that share corners with five equivalent BaS9 square pyramids, corners with four equivalent CuS5 trigonal bipyramids, edges with four equivalent CuS5 trigonal bipyramids, and faces with five equivalent BaS9 square pyramids. There are one shorter (2.35 Å) and four longer (2.41 Å) Cu–S bond lengths. There are two inequivalent S2- sites. In the first S2- site, S2- is bonded in a 4-coordinate geometry to four equivalent Ba2+ and four equivalent Cu2+ atoms. In the second S2- site, S2- is bonded to five equivalent Ba2+ and one Cu2+ atom to form a mixture of corner and edge-sharing SBa5Cu octahedra. The corner-sharing octahedral tilt angles are 14°.