Ac conductivity and relaxation processes in silver selenochromate glass

The a.c. conductivity and dielectric properties of Y% AgI-(1 - Y)%{MAg2O-F[0.6SeO(3)-0.4CrO(3)]} with Y = 20-80% glasses have been studied over the frequency range 1-10(6) Hz, by impedance measurements in the temperature range 100-300 K. The AgI dependence of conductivity is explained using the 'mixed cluster tissue to amorphous AgI aggregate' model for the glass structure. The presence of positional disorder of Ag+ ions in the AgI aggregate region is found to be responsible for the fast ionic conduction and also to the variation in conductivity with AgI composition. The a.c. conductivity is frequency independent at low frequencies and high temperatures and shows a high-frequency dispersion at low temperatures. The observed dispersion of 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 a.c. conductivity at fixed frequencies is analysed using a double exponential law with two distinct activation energies. The origin of the two activation energies observed in the a.c. conductivity is traced in the light of the jump relaxation model. The electrical modulus which describes the dielectric relaxation behaviour of the glass is fitted to a stretched exponential function, phi(t) = exp[-(t/tau)(beta)] and the results are discussed.