Isothermal section of the Y2S3-Cu2S-GeS2 system at 870Â K and crystal structures of the Y3Ge1.25S7 and Y3CuGeS7 compounds

The Y2S3-Cu2S-GeS2 system was investigated using X-ray single crystal and powder diffraction. The existence of the compounds YCuS2 (YCuS2 structure type, space group P212121) and Y0.84Cu1.48S2-Y2/3Cu2S2 (Er2/3Cu2S2 structure type, space group P3¯) was confirmed in the Y2S3-Cu2S section. The formation of the Y3Ge1.25S7 (Dy3Ge1.25S7 structure type, space group P63) compound in the Y2S3-GeS2 section was confirmed using X-ray single crystal diffraction (a = 0.9730(1) nm, c = 0.5826(1) nm, R1 = 0.0428). The formation of the compounds Cu8GeS6 (β′-Ag8GeSe6 structure type, space group Pmn21), Cu4GeS4 (Cu4GeS4 structure type, space group P21/c) and Cu2GeS3 (Cu2SnS3 structure type, space group Cc) was confirmed in the Cu2S-GeS2 section. The isothermal section of the Y2S3-Cu2S-GeS2 system at 870 K was constructed based on data of the phase analysis of 48 samples. The formation of the new quaternary Y3CuGeS7 compound (La3CuSiS7 structure type, space group P63, a = 0.9835(1) nm, c = 0.5765(1) nm), R1 = 0.0373) was established in the Y2S3-Cu2S-GeS2 system.