Effect of CaO on the conductivity and dielectric properties of novel Fe2O3·CaO·Bi2O3 glasses

Iron calcium bismuthate glasses having composition 0.05Fe2O3·0.95{xCaO·(100−x)Bi2O3} (x=30, 35 and 40 mol%) were prepared using normal melt quench technique. Complex impedance spectra of these glasses have been recorded in the temperature range 523-633 K and in the frequency range 20 Hz-1 MHz. The complex impedance data have been analyzed using the conductivity as well as electric modulus formalisms. The dc conductivity increases and activation energy decreases when CaO content increases. The modification of the glass network, due to the increase in CaO content, is responsible for the increase in conductivity. The frequency dependence of ac conductivity is found to obey the Jonscher power law. At low frequencies, dispersion was investigated in terms of dielectric loss. Significant changes in the values of the non exponential parameter (β) and the power law exponent (s) of the ac electrical properties have been observed as a function of CaO in the present glasses. A single 'master curve' for the normalized plots of all the modulus isotherms observed for a given composition indicates that the conductivity relaxation is temperature independent. The overlapping of the normalized peaks corresponding to impedance (Z″) and electric modulus (M″) suggests the same thermal activation energy for conduction and relaxation, which further suggests a single mechanism for the dynamic processes in the present glasses.