AC CONDUCTIVITY AND RELAXATION PROCESSES IN SILVER SELENOCHROMATE GLASS

The a.c. conductivity and dielectric properties of Y% AgI-(1 - Y)%{MAg 2O-F[0.6SeO(3)-0.4CrO(3)]} with Y = 20-80% glasses have been studied o ver the frequency range 1-10(6) Hz, by impedance measurements in the t emperature range 100-300 K. The AgI dependence of conductivity is expl ained using the 'mixed cluster tissue to amorphous AgI aggregate' mode l for the glass structure. The presence of positional disorder of Agions in the AgI aggregate region is found to be responsible for the fa st ionic conduction and also to the variation in conductivity with AgI composition. The a.c. conductivity is frequency independent at low fr equencies and high temperatures and shows a high-frequency dispersion at low temperatures. The observed dispersion of conductivity with freq uency is attributed to the high probability for the correlated forward -backward hopping of mobile ions in the high frequency region. The tem perature dependence of a.c. conductivity at fixed frequencies is analy sed using a double exponential law with two distinct activation energi es. The origin of the two activation energies observed in the a.c. con ductivity is traced in the light of the jump relaxation model. The ele ctrical 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.