Solid solutions in the system Ag₂S–Ag₂Se

Optical, electron microprobe, and x-ray diffraction analysis of 88 samples of various compositions between Ag₂S and Ag₂Se synthesized at high temperature in sealed quartz tubing indicates the presence of two solid-solution series in this system at ambient (room) conditions. One series extends from Ag₂S to approximately Ag₂S_0.4Se_0.7and has the Ag₂S-III-type structure (monoclinic). The second series ranges from Ag₂S_0.3Se_0.7to Ag₂Se and is characterized by the Ag₂Se-II-type structure (orthorhombic). Members of both series, in appropriate proportions, characterize the apparent compositional gap between the two solid solutions. Gradual shifts in the locations of the x-ray diffraction peaks along the compositional gradient of each solid solution revealed an expansion of thed-spacing as the larger Se ion was substituted for S in the Ag₂S-III-type structure and a contraction as S was substituted for Se in the Ag₂Se-II-type structure. The reported discrete phase, Ag₄SSe (aguilarite, orthorhombic), appears to be simply a member of the monoclinic Ag₂S-III-type solid solution.