Conductivity relaxation and ion transport processes in glassy electrolytes

The ac conductivity and dielectric relaxation properties of silver selenomolybdate glasses, Y% AgI-(1-Y)%{MAg2O-F[0.4SeO3-0.6MoO3]} with varying dopant salt concentration, Y=20-80% have been investigated as a function of frequency and temperature. The dc conductivity is found to increase by more than two orders of magnitude with increasing AgI concentration. The variation of conductivity with AgI concentration has been rationalized by considering "mixed cluster tissue to amorphous AgI aggregate" model for glass structure. The presence of positional disorder of Ag+ ions in the AgI aggregate region is found to be responsible for the observed enhancement in ionic conduction and also to the variation of conductivity with AgI concentration. The ac conductivity is frequency independent at low frequencies and follows an apparent power law, sigma(omega)proportional toomega(n) at the high-frequency region. The observed dispersion in conductivity with frequency is attributed to the high probability for the correlated forward-backward hopping of mobile ions in the high-frequency region. The temperature dependence of ac conductivity at fixed frequencies is analyzed using biexponential law with two distinct activation energies. The origin of the two activation energies observed in the ac conductivity is explained in the light of the jump relaxation model. The electrical modulus which describes the dielectric relaxation behavior of the glasses is fitted to a stretched exponential phi(t)=exp[-(t/tau)(beta)] and it obeys time-temperature superposition. (C) 2002 American Institute of Physics.