The Ag 2Se–HgSe–GeSe 2 system and crystal structures of the compounds

Abstract

The phase diagram of the quasi-ternary Ag 2Se–HgSe–GeSe 2 system at 298 K was investigated using X-ray phase analysis and metallography. The formation of five intermediate quaternary phases β (Ag ∼7.12–∼6.32Hg ∼0.44–∼0.82GeSe 6), γ (Ag ∼6.08–∼4.00Hg ∼0.96–∼2.00GeSe 6), δ (Ag 3.4Hg 2.3GeSe 6), ε (Ag ∼2.24–∼2.00Hg ∼2.88–∼3.00GeSe 6) and ∼Ag 1.4Hg 1.3GeSe 6 was established. The crystal structure of the β-phase (for the Ag 6.504Hg 0.912GeSe 6 composition) was determined using X-ray single crystal diffraction. It crystallizes in a cubic structure (space group F 4 ̄ 3m ) with the lattice parameter a=1.09026(4) nm. The crystal structure of the δ-phase (Ag 3.4Hg 2.3GeSe 6) was determined using X-ray powder diffraction (space group F 4 ̄ 3m , a=1.07767(8) nm). The crystal structure determination of the γ-phase (space group Pmn2 1) was performed for the compositions Ag 5.6Hg 1.2GeSe 6, Ag 4.8Hg 1.6GeSe 6 and Ag 4Hg 2GeSe 6 using X-ray powder diffraction. The crystal structure of the LT-Hg 2GeSe 4 compound (space group I 4 ̄ , a=0.56786(2), c=1.12579(5) nm) was confirmed by powder diffraction also.