High Ag2S-containing amorphous materials in the system Ag2S–SiS2 and their electrical properties

Concentration of conducting ions is known to be a main factor affecting ionic conductivities of glasses. Therefore, the melt-quenched Ag2S–SiS2 glasses reported by Pradel et al. (J. Non-Cryst. Solids 188 (1995) 75) were difficult to show high ionic conductivity owing to the low Ag2S content of 40–50 mol.%. We recently reported that 60Ag2S·40SiS2 amorphous sample showed electrochemical potential window of more than 2.5 V vs. Ag/Ag+ electrode and silver ion conductivity of 7×10−2 Sm−2 at room temperature (J. Mater. Chem. 12 (2002) 1094). The ionic conductivity is somewhat low for practical uses. In order to further increase the ion conductivity, we tried to prepare high Ag2S-containing amorphous samples in the system Ag2S–SiS2 by employing the high-energy ball-milling process. Our results proved that amorphous samples containing 70 and 80 mol.% Ag2S can be synthesized in a suitable milling time range, and that the amorphous samples partially transformed into Ag8SiS6 crystalline phases with further milling. The high Ag2S-containing amorphous samples showed high ionic conductivity, and the highest ion conductivity of 2.1×100 Sm−1 was obtained at 298 K for the 80Ag2S·20SiS2 amorphous sample. Those samples, however, showed very poor electrochemical stability.