SINGLE CRYSTALS GROWTH OF Ag7+x(P1-xGex)S6 (x = 0.1; 0.25; 0.33) SOLID SOLUTIONS

Abstract

Ternary silver argyrodites exhibit a wide range of properties and are classified as promising solid-state conductors, thermoelectrics, photovoltaic and nonlinear optical materials. This is ensured by the peculiarity of the crystal structure of argyrodites, which combines a rigid anionic and a disordered cationic sublattice. This work is devoted to the development of a technological regime for growing high-quality single-crystalline samples of Ag7+x(P1-xGex)S6 (x = 0.1; 0.25; 0.33) solid solutions by the method of directed crystallization from the melt. Polycrystalline alloys of Ag7+x(P1-xGex)S6 (x = 0.1; 0.25; 0.33) solid solution were obtained from previously synthesized ternary Ag7PS6 and Ag8GeS6. The synthesis was carried out by a single-stage and single-temperature method at a maximum temperature of 1010°C. The phase composition of the synthesized alloys was determined by the XRD method. Phase analysis of the obtained polycrystalline alloys did not reveal reflections of impurity phases. The results of thermal studies of Ag7+x(P1-xGex)S6 alloys were used to develop a technological regime for single crystals growth. Ag7+x(P1-xGex)S6 single crystal was grown from the melt by the directional crystallization method. As a result of the research, high-quality single crystals of Ag7+x(P1-xGex)S6 solid solutions (x = 0.1; 0.25; 0.33) were obtained. According to the results of X-ray diffraction, it was established that the solid solution of the composition Ag7.1(P0.9Ge0.1)S6 crystallizes in the primitive cubic cell of SG P213, and the solid solutions Ag7.25(P0.75Ge0.25)S6 and Ag7.33(P0.67Ge0.33)S6 crystallizes in a metastable at room temperature high-temperature modification with SG F-43m.
 Keywords: argyrodites; single crystals; directional crystallization; phase analysis.