Impedance study of 33.3Na2O-(66.7 − x)B2O3-xSiO2 glasses

Glasses with composition 33.3Na2O-(66.7 − x)B2O3-xSiO2 are studied using ac impedance. The Kohlrausch-Williams-Watts function, ϕ(t) = exp[−(t/τ0)1−n], and the coupling model are utilized for analyzing electric modulus. Conductivities increase with SiO2 contents and may differ as much as 200 times. In addition, n decrease with increasing SiO2 contents as well as temperatures. Glasses with higher SiO2 contents have smaller primitive energies (Ea). Further analyses show that the conductivities increase linearly with the ratios of the fraction of non-bridging oxygen (NBO) to the fraction of the four-coordinated boron units (N4). The increase of conductivities with SiO2 content is attributed to the smaller primitive energies for the sodium ions associated with NBO and smaller coupling interaction between ions.