The Ag2Se-HgSe-SiSe2 system in the 0-60 mol.% SiSe2 region

Phase equilibria in the quasiternary Ag2Se-HgSe-SiSe2 system were investigated using X-ray phase analysis. Its isothermal section at 298 K was constructed. The formation of the quaternary Ag6HgSiSe6 phase was confirmed. The existence of the homogeneity range for this compound at 23-43 mol.% of Hg4SiSe6 (Ag6.16-4.56Hg0.92-1.72SiSe6) was determined. The formation of three new intermediate phases Agsimilar to7.11-similar to6.32Hgsimilar to0.48-similar to0.84SiSe6 (beta), Agsimilar to3.44-similar to2.96Hgsimilar to2.28-similar to2.52SiSe6 (delta) and Ag2Hg3SiSe6 (epsilon) was found. All phases are localized along the Ag8SiSe6-Hg4SiSe6 section. The crystal structures of the beta-phase (for the Ag6.4Hg2.4SiSe6, composition) and delta-phase (for the Ag3.2Hg2.4SiSe6 composition) were determined. Both phases crystallize with a cubic unit cell (space group F (4) over bar 3m) with the lattice parameters a = 1.08806(4) nm and a = 1.07108(2) nm for the Ag6.4Hg0.8SiSe6 and Ag3.2Hg2.4SiSe6, respectively. Atomic parameters for them were refined in the anisotropic approximation [R-1=0.0830 (Ag6.4Hg0.8SiSe6) and R-1=0.0950 (Ag3.2Hg2.4SiSe6)]. The crystal structure of the epsilon-phase is under investigation. The phase diagram of the HgSe-SiSe2 system was constructed in the range 0-60 mol.% SiSe2. It was established that the Hg4SiSe6 Compound melts congruently at 1044 K and forms eutectics at similar to12 mol.% SiSe2 (1023 K) and similar to52 mol.% SiSe2 (961 K). (C) 2002 Elsevier Science B.V. All rights reserved.