Nanocomposites and nanomaterials

MECHANICAL PROPERTIES OF SUPERIONIC CERAMICS BASED ON Ag7(Si1-xGex)S5I SOLID SOLUTIONS
Shender I.O., Pogodin A.I., Filep M.J., Malakhovska T.O., Kokhan O.P., Suslikov L.M., Bilanych V.S., Pop M.M.
Uzhhorod National University, Pidhirna St. 46, Uzhhorod, Ukraine
E-mail: iryna.shender@uzhnu.edu.ua. 

Superionic conductors Ag7SiS5I and Ag7GeS5I belong to a wide family of compounds with an argyrodite structure [1]. Due to the high ionic conductivity of Ag7(Si1-xGex)S5I crystals they are promising materials for creation an efficient electrode materials, photoanodes, supercapacitors, etc. [2]. Recently, increasing attention is observed to the preparation and investigation of superionic conductors in the form of ceramics due to their greater manufacturability.
Ceramic samples of Ag7(Si1-xGex)S5I (x = 0.2, 0.4, 0.6, 0.8) solid solutions were made by sintering of pressed micro- and nanocrystalline powders. Nanocrystalline powders were obtained by grinding in a planetary ball mill PQ-N04 for 30 and 60 min, and microcrystalline powders were ground in an agate mortar. Annealing of the pressed samples was performed in evacuated quartz ampoules at 973 K for 36 h. Thus, ceramics were obtained in the form of disks with a diameter of 8 mm and a thickness of 3-4 mm. Measurements of microhardness was performed by indentation of the Vickers pyramid in the load range of 0.05-1.5 N. The depth of penetration of the indenter was 1-10 μm.
Established that the microhardness of Ag7(Si1-xGex)S5I-based ceramics decreases with increasing the depth of indentation. This is explained by the dimensional effect of indentation during microindentation of ceramics. The decrease in microhardness with decreasing Si content during the Si4+→Ge4+ substitution is observed both for the studied ceramics and single crystals. The decrease in the values of microhardness for ceramic samples compared to the single crystals is established. This is due to the porosity and presence of intercrystalline areas (with a large number of structural defects) and, as a consequence, “free” volume in the ceramics.
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1. W.F. Kuhs, The argyrodites – A new family of the tetrahedrally close-packed srtuctures// Mater. Res. Bull.-1979. Vol.14, pp. 241 – 248.
2. M. Laqibi, B. Cros, S. Peytavin, M. Ribes, New silver superionic conductors Ag7XY5Z (X = Si, Ge, Sn; Y = S, Se; Z = Cl, Br, I) – synthesis and electrical studies// Solid State Ionics.-1987.- Vol. 23, pp. 21-26.