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Cu 1-х Ag x ) 7 GeS 5 I mixed crystals grown with a vertical-zone crystallization technique are described by the cubic structure 43 F m . We analyze compositional dependences of their lattice parameter and crystal density. Diffusereflection spectra for the powders of (Cu 1-х Ag x ) 7 GeS 5 I are measured at the room temperature. Refractive indices and extinction coefficients are obtained from spectral ellipsometry measurements. When Ag content increases, we observe a nonlinear decrease in the pseudogap and a nonlinear increase in the refractive index, with a maximum. Interrelations between the structural and optical properties of (Cu 1-х Ag x ) 7 GeS 5 I are discussed.

The application of innovative resolutions that are technically grounded and economically acceptable with the use of environmentally friendly components is one of the important points at the present stage of human development to promote the ideas of efficient use of energy resources. Superionic conductors take a leading role in solving the problems of energy-saving technologies because electrochemical sensors and solid energy sources based on them can be created. Quaternary silver-containing compounds of argyrodite structure Ag6PS5I, Ag7SiS5I, and Ag7GeS5I have many advantages, in particular chemical stability, high values of ionic conductivity, the ability to form wide series of solid solutions due to the structural features. This work is devoted to the development and optimization of technology for obtaining high-quality single-crystal samples of solid solutions based on compounds of argyrodite structure formed in systems Ag6PS5I‒Ag7GeS5I та Ag7SiS5I‒Ag7GeS5I. The synthesis of solid solutions of the investigated systems was carried out by a direct single-temperature method from previously obtained quaternary compounds Ag6PS5I, Ag7SiS5I, and Ag7GeS5I. The maximal temperature of synthesis was 1273 K (exposure 72 h). Cooling to the experimentally selected annealing temperatures of 733 K (Ag6PS5I‒Ag7GeS5I) and 873 K (Ag7SiS5I‒Ag7GeS5I) was performed at a rate of 100 K/h. The annealing was performed for 120 hours. Crystal growth of solid solutions based on Ag6PS5I, Ag7SiS5I, and Ag7GeS5I phases was carried out by the directional crystallization from solution-melt by the Bridgman technique. The growth of single crystals was carried out in a three-zone furnace in a quartz container with a conical bottom. The optimal technological regimes for crystal growth of solid solutions of Ag6PS5I‒Ag7GeS5I and Ag7SiS5I‒Ag7GeS5I systems have been established. Grown single crystals of solid solutions Ag6+x(P1-xGex)S5I (х=0.25, 0.5, 0.75) and Ag7(Si1-xGex)S5I (х=0.2, 0.4, 0.6, 0.8) were dark gray color with metallic luster 30-40 mm long and 10-12 mm in diameter. Obtained crystals were investigated by X-ray diffraction analysis. Calculated lattice parameters change according to Vegard’s rule and confirm the formation of solid solutions in studied systems.

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