Formation of an endothermal Cu2In2SiS6 compound in the CuInS2–SiS2 system

Phase diagram of the CuInS2–SiS2 system in the range of 0–75 mol.% SiS2 was constructed using the results of differential thermal analysis and XRD. A new endothermal quaternary phase of the Cu2In2SiS6 composition was discovered in the system that melts incongruently at 1233 K. The eutectoid decomposition of Cu2In2SiS6 takes place at 1107 K. The crystal structure of Cu2In2SiS6 was studied by the powder method. The XRD pattern indexes in the monoclinic symmetry, space group Cc with the lattice parameters: a = 1.18725(3), b = 0.67880(2), c = 1.19718(2), β = 110.224(2)°, structure type Ag2In2GeSe6. The chalcopyrite-based solid solubility in the system extends to 9 mol.% SiS2 at 670 K. The crystal structure of the boundary composition Cu0.91In0.91Si0.09S2 of the solid solution was refined.