Influence of Bi2O3 on physical, electrical and thermal properties of Li2O·ZnO·Bi2O3·SiO2 glasses

Lithium zinc bismuth silicate glasses having composition 30Li2O·20ZnO·xBi2O3·(50−x)SiO2, (10 ⩽ x ⩽ 40 mol%) were prepared by using normal melt quenching technique. Physical, optical, electrical and thermal properties have been investigated in order to understand mixed former effect because of the presence of Bi2O3 and SiO2 in these glasses. The compositional variations of density (Dg) and molar volume (Vg) have been examined. From the optical absorption spectra, the cut-off wavelength (λg), optical band gap (Eg) and Urbach's energy (ΔE) have been determined and are related with the structural changes occurring in these glasses with increase in bismuth oxide content. The electronic polarizability of the oxide ion and optical basicity has also been obtained from the calculated values of the optical band gap. The ac and dc conductivities, activation energy for dc conduction (Edc) and for relaxation frequency (EM″) were calculated from the impedance spectra. The results obtained from dc conductivity depicted that the lithium ions are mainly responsible for the conduction mechanism and it also confirmed the network forming role of zinc oxide in these glasses. The temperature dependence of the relaxation dynamics in these glasses has been interpreted by using the scaling of the conductivity spectra. The observed conductivity spectra follows power law with exponent 's' which decreases with temperature and satisfies the correlated barrier hopping (CBH) model. The exact overlying of normalized plots of electrical modulus on a single 'master curve' indicates temperature independent dynamical process at various frequencies. The non-linear compositional change in optical band gap, activation energies as well as glass transition temperature reveals the mixed glass former effect. The increase in the values of thermal parameters such as glass stability factor and Hruby's parameter, suggests large stability of glasses.