Influence of SiO2 on the structural and dielectric properties of ZnO∙Bi2O3∙SiO2 glasses

Abstract

Zinc bismuth silicate glasses having composition 20ZnO∙(80-x)Bi₂O₃∙xSiO₂ (with x = 0, 10, 20, 30, 40 and 50 mol%) were prepared by the conventional melt-quench technique. The compositional dependence of density (D), molar volume (V_M) and glass transition temperature (T_g) were analyzed and correlated with the structural changes occurring in the glasses. The FTIR spectra were recorded in the range 400-4400cm^-1 in order to obtain information about the competitive role of Bi₂O₃ and SiO₂ in the formation of glass network. From the analysis of these spectra it is found that in these glasses, Bi₂O₃ acts as both network former with [BiO₃] pyramidal units and as modifier with [BiO₆]octahedral units. The formation of Zn²⁺ in tetrahedral co-ordination was not observed. Conduction and relaxation mechanism in these glasses were studied using impedance spectroscopy in the frequency range from 10Hz to 7MHz and in the temperature range from 473 to 703 K. The ac and dc conductivities, activation energy for dc conduction (E_dc) and relaxation (E_Ï„) were extracted from the impedance spectra. The compositional variation in conductivity has been attributed to the presence of mixed glass former effect in these glasses. The perfect overlapping of normalized plots of electrical modulus on a single ‘master curve’ for all temperatures reveals that the conductivity relaxation occurring at different frequencies exhibit temperature independent dynamical processes. Similar values of E_dc and E_Ï„ for each glass composition indicate that the charge carrier ions have to overcome the same energy barrier during conduction as well as relaxation processes.