Phase diagram of the Ag 2S–HgS–SnS 2 system and single crystal preparation, crystal structure and properties of Ag 2HgSnS 4

Abstract

The phase equilibria in the quasi-ternary system Ag 2S–HgS–SnS 2 at 298 K were investigated using X-ray diffraction. The existence of the Ag 2HgSnS 4 compound that is the only one at this temperature was confirmed. The vertical section Ag 8SnS 6–HgS was constructed. It is of the eutectic type (eutectic point coordinates are 89 mol% HgS and 881 K), with the formation of a HT–Ag 8SnS 6 solid solution range extending to ∼57 mol% HgS at 881 K. The Ag 2HgSnS 4 crystal structure was refined using X-ray powder diffraction. Ag 2HgSnS 4 crystallizes in the orthorhombic space group Pmn2 1 (ST Cu 2CdGeS 4) with unit cell parameters a = 0.82074(4) nm, b = 0.70330(3) nm and c = 0.67180(3) nm. The atomic parameters were refined in the isotropic approximation to R = 0.0795. Ag 2HgSnS 4 single crystals ( Ø = 10–12 mm; l = 30 mm) were grown using the Bridgman–Stockbarger technique. The single crystals exhibit n-type semiconductor conductivity. The photoconductivity spectra at liquid nitrogen and room temperatures were investigated, and their non-elementary nature was shown.