Phase diagram of the Ag2S-HgS-SnS2 system and single crystal preparation, crystal structure and properties of Ag2HgSnS4

The phase equilibria in the quasi-ternary system Ag2S-HgS-SnS2 at 298 K were investigated using X-ray diffraction. The existence of the Ag2HgSnS4 compound that is the only one at this temperature was confirmed. The vertical section Ag8SnS6-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-Ag8SnS6 solid solution range extending to ∼57 mol% HgS at 881 K. The Ag2HgSnS4 crystal structure was refined using X-ray powder diffraction. Ag2HgSnS4 crystallizes in the orthorhombic space group Pmn21 (ST Cu2CdGeS4) 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. Ag2HgSnS4 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.