Influence of Bi2O3 on thermal, structural and dielectric properties of lithium zinc bismuth borate glasses

The quaternary glass system 30Li2O⋅20ZnO⋅xBi2O3⋅(50−x)B2O3 (with x = 0, 10, 20, 30, 40 and 50 mol%), were fabricated by the conventional melt quench technique. The characterization of the samples include physical properties (density and molar volume), thermal properties using differential scanning analysis, structural studies using IR spectroscopy, optical properties using UV-VIS-NIR spectroscopy and dielectric properties using impedance spectroscopy. Density and molar volume variations with glass composition have been discussed. The non-linear compositional change in glass transition temperature and result obtained from IR studies confirm that Bi2O3 play dual role i.e. as network modifying oxide as well as network forming oxide. Also, the significant shifting of band at 1384-1305 cm−1 with increase in Bi2O3 content in the glass matrix suggests the formation of new boron-oxygen ring. The presence of sharp cut-off and large transmission in UV-VIS-NIR regime make these glasses suitable for spectral devices. The cut-off wavelength, optical band gap and Urbach's energy were determined from the absorption spectra and were related with the structural changes occurring in these glasses with increase in Bi2O3:B2O3 ratio. The complex impedance plots show depressed semicircles that shift towards origin with increase in temperature. This reveals the migration of charge carrier ions in glass matrix is thermally stimulated. The frequency-dependent complex impedance data were analyzed in the framework of conductivity and modulus formalisms. The dc conductivity decreases with increase in Bi2O3 content (<40 mol%) because of blocking effect of the Bi ions on the migration of mobile ions. The observed maximum in Edc for LZBB 4 sample implies the existence of mixed former effect in these glasses. The perfect overlapping of normalized plots of electrical modulus on a single 'master curve' suggests temperature independent dynamical process at different frequencies.