Dispersion in AC conductivity of fragile glass melts near glass transition temperature

We analyzed scaling behaviour of conductivity spectra of two fragile glass melts 2Ca(NO3)2.3KNO3 (CKN) and 2Ca(NO3)2.3RbNO3 (CRN) below and above their glass transition temperature (TG). Spectra were described in terms of power law. Conductivity isotherms of these systems were found to follow time temperature superposition principle (TTSP) below and above TG and can be scaled to a master curve using hopping frequency as scaling factor. However, for both the systems, a deviation from TTSP was discerned in the vicinity of TG. We also observed, for both CKN and CRN, a change in exponent factor of the power law and in number density of the mobile charge carriers around TG. The experimental data were also analyzed in terms of electric modulus mechanism. Both, conductivity and modulus formulism revealed the similar trend of TTSP behaviour. The deviation from TTSP near TG has been correlated with the changes observed in these two quantities. Further, it has been proposed that the magnitude of change in dispersion of conductivity spectra is directly related with the decoupling and fragility of the glass melt systems.