Impedance and modulus spectroscopic studies on (CuI)100-x-(Ag2SO4)x (0 ≤ x ≤ 60) mixed system

Abstract

The frequency-dependent conductivity, σω measurements on (CuI)100-x-(Ag2SO4)x (0≤x≤60) mixed system in the frequency range 1 Hz–65.5 kHz and over the temperature range 293–403 K have been carried out. These studies have illustrated similarities in the behaviour of the present system and the other fast ionic solid systems which are generally found to obey the Jonscher's universal power law, σa.c.(ω)=σ0+Aωn, where σa.c.(ω) is the conductivity at frequency ω, σ0 is the limiting zero frequency conductivity or d.c. conductivity and A and n are fitting parameters. The value of n decreases with increasing temperature and A and σ0 increase with temperature (n is a temperature-dependent frequency exponent, A is a frequency-independent and temperature-dependent parameter). These results appear to suggest a mechanism of fast ion conduction due to the presence of well-defined pathways. The strong low-frequency dispersion observed in the case of high conductivity compositions is attributed to the electrode polarization effects. The observed impedance and modulus spectra in correlation with the Arrhenius plots obtained at different frequencies have clearly indicated the frequency dispersion of conduction due to many-body effects and the formation of a large capacitance associated with the electrodes. Thus, the present analysis has suggested a non-Debye type of relaxation process arising due to many-body effects and a distribution of relaxation times, which is a temperature-independent phenomenon exhibited by the heterogeneous electrical structure of the mixed system.