Compounds with an argyrodite structure are a family of complex chalcogenides that demonstrate a wide range of properties: superionics, thermoelectrics, sensors, and photovoltaic materials. For sulfur-containing representatives, the main field of application is solid-state ionics. However, the formation of solid solutions is used to modify and improve the functional parameters of individual argyrodites. When solid solutions are formed by iso- or heterovalent substitution, an additional deformation of the crystal structure occurs, which increases the efficiency of ion transport. For the growth of single crystals, the method of direct crystallization by melt-solution technique was used. Based on the results of DTA, technological conditions for growing single crystals of solid solutions of Ag7.75P0.25Si0.75S6 and Ag7.5P0.5Si0.5S6 were developed. The temperature of the melt zone (Tmelt) was 50 K higher than the melting point of the solid solutions, and the temperature of the annealing zone (Tann) was 2/3 of their crystallization temperature determined by the DTA method. As a result, single crystals of dark gray color with a metallic luster were obtained. The crystal structure of the solid solutions of Ag7.75P0.25Si0.75S6 and Ag7.5P0.5Si0.5S6 was determined by the Rietveld method. Both solid solutions crystallize in a rhombic crystal system, SG Pna21, with lattice parameters: a = 15.06 Å, b = 7.44 Å, c = 10.54 Å (Ag7.75P0.25Si0.75S6) and a = 15.06 Å, b = 7.44 Å, c = 10.54 Å (Ag7.5P0.5Si0.5S6).
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