Phase relations in the quasi-binary Cu2GeS3-ZnS and quasi-ternary Cu2S-Zn(Cd)S-GeS2 systems and crystal structure of Cu2ZnGeS4

The isothermal section of the Cu2S-Zn(Cd)S-GeS2 systems at 670 K was constructed using X-ray diffraction analysis. At this temperature, two quaternary intermediate phases, Cu2CdGeS4 and ∼Cu8CdGeS7, exist in the Cu2S-CdS-GeS2 system, and only one phase, Cu2ZnGeS4, exists in the Cu2S-ZnS-GeS2 system. The phase diagram of the Cu2GeS3-ZnS system was constructed using differential-thermal analysis and X-ray diffraction, and the existence of Cu2ZnGeS4 has been confirmed. It forms incongruently at 1359 K. Powder X-ray diffraction was used to refine the crystal structure of Cu2ZnGeS4, which crystallizes in the tetragonal stannite-type structure at 670 K (space group I4¯2m, a = 0.534127(9) nm, c = 1.05090(2) nm, RI = 0.0477). The possibility of the formation of quaternary compounds in the quasi-ternary systems AI2X-BIIX-CIVX2, where AI-Cu, Ag; BII-Zn, Cd, Hg; CIV-Si, Ge, Sn and X-S, Se, Te is discussed.