ELECTRONIC CONDUCTIVITY AND CURRENT INSTABILITY IN SUPERIONIC CRYSTALS

The current-voltage characteristics of -Ag\RbAg4I5\C+ cell are measure d and described in terms of a model assuming that the electron current across the electrochemical cell is essentially defined by the transfe r of electrons through the interface. The position of the Fermi level in the band gap and the value of the electronic conductivity sigma(e) similar or equal to 2.5 x 10(-9) Omega(-1) cm(-1) are determined. The role of the near contact region and silver dendritic clusters in the p rocess of electron transport in RbAg4I5 superionic crystals are studie d. The onset of the exponential rise of the current at increasing volt age V (at V greater than or equal to 450 mV) is described within the m odel based on the conception that the silver dendritic clusters fracta lly grow at the interface. It is shown that the increase of the voltag e leads to growth of the effective interface area (due to the cluster structure formation) and as a result to the exponential increase of th e current through the cell at V greater than or equal to 450 mV. At co nstant voltage on the cell we observed experimentally the electronic c urrent instability. We suppose that at this voltage some of the cluste rs reach the opposite electrode that leads to stochastic current oscil lations. The number of these clusters increases with the voltage growt h and therefore the current oscillations become more frequent. All exp erimental data are well described within the framework of the theory o f reversible diffusion limited aggregation without branching.