Solid solutions in the system Ag₂S–Ag₂Se

Abstract

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 Ag2S0.4Se0.7 and has the Ag2S-III-type structure (monoclinic). The second series ranges from Ag2S0.3Se0.7 to 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 the d-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.

Formation and phase transition of argyrodite type Ag7TaSe6S6(1−) solid solution

“…The transition temperature decreases from 263 to 173 K in the range 0 ≤ x ≤ 0.3, whereas it increases from 171 to 323 K in the range 0.62 ≤ x ≤ 1. This behaviour of decrease in transition temperatures away from the two pure end-member compositions closely resembles that found in the system Ag 2 S-Ag 2 Se by Pingitore et al [7,8]. The occurrence of thermal minima could be explained as follows.…”

Sulfur–selenium isomorphous substitution and polymorphism in the Ag2(S,Se) series

“…The Ag 2 SAg 2 Se chalcogenides are characterized by the presence of phase transitions and structure phase transformations [1][2][3][4][5]. Roy et al [6] suggested using silver sulfide and selenide transitions as geologic thermometers.…”

“…Roy et al [6] suggested using silver sulfide and selenide transitions as geologic thermometers. The low temperature forms of Ag 2 S and Ag 2 Se are intrinsic semiconductors, the high temperature allotropes are conductors [2,3]. Ag 2 S, Ag 4 SSe and Ag 2 Se have recently attracted considerable attention due to their optical, electrical, and thermoelectric properties [7].…”

“…Ag 2 S, Ag 4 SSe and Ag 2 Se have recently attracted considerable attention due to their optical, electrical, and thermoelectric properties [7]. Differential scanning calorimetry demonstrates that the samples of various compositions between Ag 2 S and Ag 2 Se synthesized at high temperature in sealed quartz tubing undergo rapid, reversible solid-state phase changes at temperatures between approximately 70 and 178°C [2,3]. These temperatures vary with composition, with maximal values for pure end members Ag 2 S (178°C) and Ag 2 Se (134°C), and a minimum in the compositional range between Ag 2 S 0.4 Se 0.6 to Ag 2 S 0.3 Se 0.7 (70°C).…”

“…Selenium enters into metal sulfides as an isomorphic impurity to form continuous series of solid solutions such as PbSPbSe, FeS 2 -FeSe 2 , and HgS-HgSe [8]. The possible solid solution between Ag 2 S and Ag 2 Se has been debated for a long time [1][2][3]9,10]. It is obvious that continuous isomorphic series may exist only for the end members having crystal structures of the same type.…”