SINGLE CRYSTALS GROWTH IN THE HOMOGENEITY REGION OF LOW-TEMPERATURE MODIFICATION OF Ag8GeS6

Abstract

Cationic ion-conductors have found wide practical application as electric batteries. Among them the lithium-ion batteries are the most common commercially used. However, research is being actively carried out to improve the safety of these batteries. Among the possible compounds, silver-containing phases are attractive, since silver-ions, along with high values of ionic conductivity in solid-state, haven’t high chemical activity like the same alkali metal-ions. Realization of the crystal structure necessary for effective ion transport is observed in compounds of the argyrodite structure - a group of ternary chalcogenides and quaternary chalcohalogenides of multi-charged cations (Ge4+, Si4+, P5+). In this work, a study of heterovalent cationic P5+→Ge4+ substitution in the Ag8GeS6 enriched region was carried out. Single crystals of Ag8-x(Ge1-xPx)S6 (x = 0.25; 0.5) solid solutions were grown by the method of directional crystallization using a solution-melt technique. The grown single crystals are characterized by the absence of macrodefects, a dark gray color with a metallic luster, and dimensions of l = ~3 cm and d = 1.2 cm. Using the Rietveld refinement method, the crystal structure was established and the lattice parameters of Ag8-x(Ge1-xPx)S6 (x = 0.25; 0.5) solid solutions were determined. Established, that single crystals of Ag8-x(Ge1-xPx)S6 (x = 0.25; 0.5) solid solutions crystallize in the orthorhombic crystal system in a primitive cell with space group Pna21.
 Keywords: argyrodites; single crystals; directional crystallization; phase analysis.