STRUCTURAL AND ELECTRICAL PROPERTIES OF MONOCRYSTALLINE Ag7+xGexP1-xS6 (x = 0.75; 0.5) SOLID SOLUTIONS

Abstract

Compounds of the argyrodite structure are considered to be promising functional materials due to their peculiarities. The functional parameters of these compounds are provided by the peculiarities of the crystal structure, namely the simultaneous coexistence of a mobile cationic sublattice within a rigid anionic framework. Such a crystal structure motif determines the formation of wide regions of solid solutions based on argyrodites and makes it possible to increase the values of the functional parameters of these phases within the homogeneity regions. This work presents the results of the study of the structural and electrical properties of Ag7+xGexP1-xS6 (x = 0.75; 0.5) solid solutions with an argyridite structure. Single-crystal samples of solid solutions of Ag7.75Ge0.75P0.25S6 and Ag7.5Ge0.5P0.5S6 were obtained by the method of directional crystallization from the melt in vacuum-sealed quartz ampoules. It was found that the solid solutions of Ag7+xGexP1-xS6 (x = 0.75; 0.5) crystallize in orthorhombic crystal system: SG Pna21, with lattice parameters: a = 15.093 Å, b = 7.462 Å, c = 10.571 Å (Ag7.75Ge0.75P0.25S6) and a = 15.023 Å, b = 7.450 Å, c = 10.545 Å (Ag7.5Ge0.5P0.5S6). The frequency and temperature dependence of the total electrical conductivity was studied by impedance spectroscopy. The total electrical conductivity of the investigated single crystals is Ag7.75Ge0.75P0.25S6 5.43×10–3 S/cm (0.199 eV) and Ag7.5Ge0.5P0.5S6 2.22×10–2 S/cm (0.152 eV) at a temperature of 25 °C.
 Keywords: argyrodites; single crystals; electrical conductivity; phase analysis.