Frequency dispersion of the ionic conductivity of RbAg4I5 at low temperatures

The ionic conductivity of the superionic conductor RbAg4I5 was studied at l ow temperature using a modified electrochemical impedance spectroscopy (EIS ) as well as dielectric measurements (DM). Experiments using RbAg4I5 sample s of constant crystal imperfection density were carried out in the temperat ure range 50 K less than or equal to T less than or equal to 110 K and in t he frequency range 10(1) Hz less than or equal to f less than or equal to 1 0(7) Hz. The current data are in good agreement with previous low-frequency EIS measurements carried out in the frequency range 10(-3) Hz less than or equal to f less than or equal to 10(5) Hz and high-frequency wave-guide me asurements in the frequency range 18 GHz less than or equal to f less than or equal to 40 GHz. The results confirm a nearly temperature-independent lo w-frequency ionic conductivity below a transition temperature T < T-t = (75 +/-15) K which is caused by a change of the ion conduction mechanism. At T > T-t, the ion transport occurs through grains and subgrains crossing grain and subgrain boundaries, whereas at T < T,, the ion transport takes place only via crystal imperfections, i.e. along grain and subgrain boundaries. F inally, the new results presented feature a frequency dispersion of the ion ic conductivity in the mid frequency range which follows a power law with a n exponent of p = 1 +/- 0.1, thus confirming the so-called 'new universalit y' law. (C) 1999 Elsevier Science B.V. All rights reserved.