The System Ag-S-Se: Phase Relations, Electrical and Opticalperties, and Applications

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The system Ag-S-Se is of considerable interest in materials research due to the optical, electrical, and thermo-electrical properties which typify these elements in the solid state. Three compounds are generally recognized as characterizing the system at room temperatures: Ag2S (monoclinic), Ag4SSe (orthorhombic), and Ag2Se (orghorhombic). Recently we have synthesized a series of intermediate compounds ranging in composition from the pure silver sulfide, through the silver sulfo- selenide, to the pure silver selenide. The compositional series appears to break into two solid solutions, one extending from Ag2S to approximately Ag4SO.65Se1.35 and the other encompassing Ag4SO.65Se1.35 to Ag2Se. In this project we hope to: 1.) Produce the phase diagram for the system Ag-S-Se and confirm the crystallography of the two solid solutions. 2.) Document the electrical, optical, and thermoelectric properties of these compounds. 3.) Investigate the fabrication of these materials as thin films. 4.) Determine possible commercial applications (e.g., dry cells, thermal sensors, electrochromic displays, non-linear optoelectronic devices) of these materials. This project represents the first look at the behaviors of new materials that are likely to possess interesting electrical, optical, and thermoelectric properties. Because the materials form solid solutions, their behaviors should be continuously variable with composition, with the potential for the creation of "designer properties" based on stoichiometry.