Synthesis, crystal structure, and optical properties of Ba2Cu2ThS5, and electronic structures of Ba2Cu2ThS5 and Ba2Cu2US5

International audienceThe compound Ba2Cu2ThS5 has been synthesized by the reaction of BaS, S, Cu, and Th at 1173 K. It crystallizes in the monoclinic space group C-2h(3)-C2/m with two formula units in a cell of dimensions a=13.5616(8) angstrom, b=4.1159(2) angstrom, c=9.3548(6) angstrom, beta=115.89(1) (100 K). The structure comprises Ba2+ cations and (2)(infinity)[Cu2ThS54-] layers. The two dimensional layers are formed by the connection of ThS6 octahedra and CuS4 tetrahedra along [001] with a sequence .... oct tet tet oct tet tet .... Optical measurements performed on Ba2Cu2ThS5 indicate an indirect band gap of 1.86 eV. DFT calculations performed with the HSE06 functional yield band gaps of 1.7 eV for Ba2Cu2ThS5 and 1.5 eV for the isostructural compound Ba2Cu2US5