Phase diagrams of the quasi-binary systems Cu 2S–SiS 2 and Cu 2SiS 3–PbS and the crystal structure of the new quaternary compound Cu 2PbSiS 4

Abstract

X-ray phase analysis was used to investigated nine alloys with the general formula Cu 2PbB IVX 4 where B IV – Si, Ge, Sn; X – S, Se, Te. Only one compound of such composition was found, namely Cu 2PbSiS 4. Using differential thermal and X-ray phase analysis results, the phase diagrams of the Cu 2S–SiS 2 (in 0–60 mol% SiS 2 range) and Cu 2SiS 3–PbS systems were constructed. A congruent type of formation of Cu 8SiS 6 and Cu 2SiS 3 at 1459 and 1201 K, respectively, was confirmed in the Cu 2S–SiS 2 system. The Cu 2SiS 3–PbS system is quasi-binary with the formation of two quaternary intermediate phases, ∼Cu 4PbSi 2S 7 and Cu 2PbSiS 4. The ∼Cu 4PbSi 2S 7 compound forms incongruently at 1024 K, and has a polymorphous transition at 933 K. Cu 2PbSiS 4 melts in peritectically at 963 K and is also dimorphous. The phase transition temperature increases with PbS content in the 883–915 K range. The crystal structure of the low-temperature (LT) Cu 2PbSiS 4 modification was determined using powder method. It has trigonal symmetry (space group P3 221, a = 0.60565(2), c = 1.51841(5) nm, R I = 0.0641).