Germanate glasses containing lead and bismuth oxides: Correlation between elastic and compositional parameters

Elastic properties of germanate GeO2-PbO and GeO2-PbO-Bi2O3 glasses have been interpreted and predicted in order to explore the structural role of PbO and Bi2O3 in the germanate network. To establish the applicability of Makishima-Mackenzie's theory and Rocherulle et al. model for these glasses, the theoretical elastic moduli and Poisson's ratio were evaluated and compared with the experimental ones. The basic compositional and structural parameters were calculated and correlated with elastic properties. PbO changes the continuous germanate network to the continuous lead-germanate network by formation of PbO4 and GeO6 units, in addition to GeO4 units. Whereas Bi3+ ions occupy interstitial positions in GeO2-PbO-Bi2O3 glasses by formation of deformed BiO6 octahedral units. Both Makishima-Mackenzie's theory and Rocherulle et al. model are valid for majority of samples. The divergence between theoretical and experimental data was attributed to the anomalous behavior between the calculated dissociation energy per unit volume and elastic moduli.