Mechanical vs electrical relaxation in Agl-based fast ion conducting glasses

Results of a low frequency mechanical relaxation study of a fast ion conducting system, and comparison of mechanical with electrical conductivity relaxation in the same system, are reported, using the system AgI + AgPO₃. As predicted from conductivity studies, the mechanical relaxation in the highest conducting glasses occurs at very low temperatures ∼ -170°C. Studies of the system AgIAgBO₂ and exploratory work on mixed oxyanion glasses are also reported. The tensile (Young's) moduli are consistent with values recently obtained from GHz range light-scattering studies. The dispersion in Young's modulus due to the fast ion relaxation is very large, even exceeding those seen in mixed alkali glasses, and it occurs over a much wider temperature range than the corresponding dispersion in the electrical modulus, even though the loss peaks occur within 3 K of one another. The electrical and mechanical loss peaks are found to have the same temperature dependence, and this fact is used to develop a reduced representation of the mechanical relaxation data, suitably normalized in frequency space (ωτ). Both the normalized loss peak height and halfwidth in this representation imply exceptional departures from exponential relaxation with β = 0.25 in the Kohlrausch decay function Θ(t) = exp - ([t/τ]^β). The mechanical relaxation evidently has elements both slower and faster than those characterizing the electrical relaxation. A general "relaxation map" of τ vs 1/T for mechanical and electrical phenomena in this system is proved.