The conductivity of the superionic conductor was studied at low temperatures by using modified electrochemical impedance spectroscopy as well as dielectric measurements. Experiments, using samples of constant crystal imperfection density, were carried out at 50 to 110K and 10Hz to 1MHz. The current data were in good agreement with previous low-frequency electrochemical impedance spectroscopic measurements carried out at 1mHz to 0.1MHz and high-frequency wave-guide measurements performed at 18 to 40GHz. The results confirmed an almost temperature-independent low-frequency ionic conductivity below a transition temperature, Tt (75K), which was caused by a change in the ionic conduction mechanism. At T > Tt, ionic transport occurred through grains and sub-grains crossing grain and sub-grain boundaries. At T < Tt, ion transport took place only via crystal imperfections (along grain and sub-grain boundaries). These results revealed a frequency dispersion, of the ionic conductivity in the mid-frequency range, which obeyed a power law with an exponent of unity; thus confirming the so-called new universality law.

Frequency Dispersion of the Ionic Conductivity of RbAg4I5 at Low Temperatures. E.C.Bucharsky, R.T.Pötzschke, G.Staikov, E.Budevski, W.J.Lorenz, W.Wiesbeck: Solid State Ionics, 1999, 124[1-2], 101-8