Phase relations in the Ag2S-CdS-SnS2 system and the crystal structure of the compounds

Based on the results of X-ray phase analysis, an isothermal section of the quasi-ternary system Ag2S-CdS-SnS2 at 298 K was constructed. The existence of the Ag2CdSnS4 compound was confirmed, and a new quaternary phase Ag2CdSn3S8 was discovered. The crystal structure of both compounds was refined using X-ray powder method. Ag2CdSnS4 crystallizes in the orthorhombic space group Cmc21 with the unit cell parameters a = 0.41015(3), b = 0.70224(4), c = 0.66946(4) nm (RI = 0.0550). The Ag2CdSn3S8 crystal structure refines well in both the tetragonal structure of the rhodostannine type (space group I41/a, a = 0.76163(6), c = 1.0771(2) nm, RI = 0.0750) and the cubic structure of the chalcospinel type (space group Fd3¯m; a = 1.07635(2) nm, RI = 0.0781). The phase diagram of the Ag8SnS6-CdS section was constructed, which is of the eutectic type. The eutectic point coordinates are ∼47 mol.% CdS and 1082 K.