Phase diagram of the AgGaS2–PbGa2S4 system

Lead and silver thiogallates are notable for their practical applications in nonlinear optical devices, detectors, solar cells, photodiodes, and phosphors. This study aims to develop materials with multifunctional properties and investigate the AgGaS2–PbGa2S4 system. The initial sulfides, AgGaS2 and PbGa2S4, were synthesized from high-purity elements sealed in evacuated quartz ampoules (0.133 Pa). Complex alloys of the AgGaS2–PbGa2S4 system were prepared at 1200–1350 K. Polycrystalline samples were annealed at 850 K for 270 hours. Phase equilibria in the AgGaS2–PbGa2S4 system were analyzed using a combination of physicochemical methods, including differential thermal analysis, powder X-ray diffraction, microstructural analysis, microhardness, and density measurements, and the phase diagram was constructed. The system was identified as a quasi-binary section of the quasi-ternary Ag2S–Ga2S3–PbS system, belonging to the eutectic type. The eutectic point was determined at 1100 K and 55 mol.% PbGa2S4. Solid solution regions were identified based on the primary components. At room temperature, the AgGaS2 solid solution region extends to 10 mol.% PbGa2S4, while the PbGa2S4 solid solution region extends to 18 mol.% AgGaS2. At the eutectic temperature, these solubilities increase to 20 and 25 mol.%, respectively. AgGaS2-based solid solutions crystallize in chalcopyrite-type structures, while PbGa2S4-based solid solutions adopt orthorhombic structures.