Dielectric study and ac conductivity of iron sodium silicate glasses

A series of glasses with formula (SiO2)(0.7-x)(Na2O)(0.3)(Fe2O3)(x) with (0.0 <= x <= 0.20) were prepared and studied by means of AC measurements in the frequency range 20 kHz to 13 MHz at room temperature. The study of frequency dependence of both dielectric constant epsilon' and dielectric loss epsilon '' showed a decrease of both quantities with increasing frequency. The results have been explained on the basis of frequency assistance of electron hopping besides electron polarization. From the Cole-Cole diagram the values of the static dielectric constant epsilon(s), infinity dielectric constant epsilon(infinity), macroscopic time constant tau, and molecular time constant tau(m) are calculated for the studied amorphous samples. The frequency dependence of the ac conductivity obeys a power relation, that is sigma(ac)(omega) = A omega(s). The obtained values of the constant s lie in the range of 0.7 <= s <= 1 in agreement with the theoretical value which confirms the simple quantum mechanical tunneling (QMT) model. The increase in ac conductivity with iron concentration is likely to arise due to structural changes occurring in the glass network. The structure of a glass with similar composition was published and showed clustering of Fe2+ and Fe3+ ions which favor electron hopping and provide pathways for charge transport. (C) 2011 Elsevier B.V. All rights reserved.