Silver diffusion anomaly in Cu–Ag–As–Se glasses: a chalcogen site analysis using 125Te-Mössbauer spectroscopy

125Te-Mössbauer spectroscopy was used in order to study the change in the local chalcogen environment of Cu–Ag–As–Se glasses showing anomalies in the Ag+ ion transport. These ion-conducting glasses with a constant silver content of 15 at.% and variable copper concentration, x, exhibit (i) a dramatic decrease in the 110Ag tracer diffusion coefficient, DAg, by two orders of magnitude at 0⩽x⩽10, and (ii) a nearly complete DAg recovering at 10⩽x⩽20. The parabolic shape of DAg is accompanied by a similar composition dependence of the quadrupole splitting, QS, which reflects changes in the Te–M (M=Ag, Cu) and Se–Ag interatomic distances. The minimal chalcogen – silver distance at x=10 at.% Cu corresponds to the minimal value of DAg.