Short-Range Structure, Thermal and Elastic Properties of Binary and Ternary Tellurite Glasses

Glasses Al_2/3O-TeO₂, ZnO-TeO₂ and R_2/3O-ZnO-TeO₂ (R = Al, B) were prepared by melting in Pt crucibles and studied for correlations between structure and thermal as well as mechanical properties, whereby the glass composition is varied to tailor the short-range speciation of tellurite, aluminate, and borate groups. The glass structure was studied by Raman and infrared spectroscopy analyses, and the measured properties include glass-transition temperature (T_g), density (ρ), and ultrasonic longitudinal (V_L) and transverse (V_T) velocities. In addition, atomic packing density (C_g), elastic moduli, and Poisson's ratio (σ) were evaluated from the measured properties. It was found that Al_2/3O leads to cross-linked alumino-tellurite networks by strong Te-O-Al bonds, which cause a profound enhancement in T_g. The influence of ZnO and B_2/3O on T_g is relatively smaller due to the weaker cross-linking effects of ZnO₄ tetrahedra and of Te···O-B bonds. Short-range bonding characteristics, interatomic bonding energy differences, and atomic packing density were found to have a strong effect on V_T and mostly on the V_L sound velocity. The combined effects of structure and bonding are nicely expressed in the composition dependence of Poisson's ratio; it exhibits decreasing trends with Al_2/3O content in the binary and ternary glasses studied here, but increasing trends with ZnO and B_2/3O additions in glasses ZnO-TeO₂ and B_2/3O-ZnO-TeO₂, respectively. The results for Poisson's ratio and atomic packing density for the studied glasses were found to fit nicely in the global σ versus C_g correlation established previously for a range of glasses not including tellurites so far. Finally, the sound velocities and Poisson's ratio of pure TeO₂ glass were determined for the first time and found to differ markedly from those in the literature for TeO₂ glass melted in alumina crucible; this is because the latter glass is highly doped by Al₂O₃ leached from the alumina crucible.