Conductivity relaxation of sol-gel derived glasses

Glasses in the system XNa₂O+(1-X)SiO₂ with X varying from 0.096 to 0.242 have been prepared by the sol-gel technique. The electrical conductivity of these materials has been investigated in the temperature range 400-600 K over frequencies varying from 10 Hz to 10 MHz. The bulk electrical resistivity has been determined by the complex impedance analysis. The AC relaxation spectrum has been studied by using the complex dielectric modulus M*=1/ epsilon *. The modulus data have been analysed by the Kohlrausch-Williams-Watts (KWW) stretched exponential function. The exponent beta is found to have a value of the range 0.28-0.40 depending on the glass composition. The beta value for a melt-quenched glass of comparable composition is found to be higher than these values and this difference is believed to arise due to the gel route of glass preparation. The activation energy for DC conductivity is found to be appreciably higher than that for AC conduction.