Frequency‐Dependent Conductivities of RbAg4I5 and Na‐β″‐Alumina from Radio to FIR Frequencies

The electric conductivities of the two fast ionic conductors RbAg4I5 and Na‐β″‐alumina have been determined at various temperatures and frequencies from 4 MHz to 105 GHz. – The conductivity of RbAg4I5 is found to display a dispersion as expected by the so‐called “universal dynamic” response, a high‐frequency plateau in the range of 100 GHz and an Arrhenius behaviour at both low and high frequencies. – The spectra of Na‐β″‐alumima show a different behaviour. In addition to the “universal dynamic” response dispersion, a faster and thermally less activated relaxation process is observed at high frequencies and low temperatures. Up to 60 GHz, a high‐frequency plateau has not been encountered.