Ion dynamics in mechanochemically synthesized amorphous fast ionic conductor Ag2S-Sb2S3

Frequency dependent electrical conductivity (σ′) of mechanochemically synthesized amorphous fast ion conductors (FICs) xAg2S-Sb2S3 (x=70, 80, 85) is investigated in the frequency range 5 Hz-13 MHz and temperature range 95-385 K. While the universal dynamic response (UDR) model, σ′ (ω)=σdc(T)+A(T)ωn, does reproduce the shape of σ′ (ω) spectra, the σdc(T) and A(T) show anomalous characteristics. Both exhibit two distinct Arrhenius regions, a low temperature region with a lower value of activation energy (E) and a high temperature region with higher value of activation energy. Further the frequency exponent n is a (decreasing) function of temperature, decreasing slowly at lower temperatures but more rapidly at higher temperatures. The correlation Eac=(1−n)Edc appears satisfactory in the low temperature region but unsatisfactory at higher temperatures. The isochronal representation of ac conductivity, σ′ vs. 1000/T at different frequencies, reveals the existence of a third regime, which is currently under active discussion and is known as superlinear power law (SLPL).