Effects of annealing on density, glass transition temperature and structure of tellurite, silicate and borate glasses

Abstract

Barium tellurite, lead tellurite, molybdenum tellurite, lead silicate and bismuth borate glasses of the compositions: xBaO-(100-x)TeO2 (x=10, 15 and 20 mol%), xPbO-(100-x)TeO2 (x=15 and 20mol%), 25MoO3-75TeO2, xPbO-(100-x)SiO2 (x=50, 60 and 65 mol%) and 40Bi2O3-60B2O3 were prepared by melt-quenching. The effects of long duration thermal annealing (below the respective glass transition temperature (Tg) values) on the density, thermal properties and the short-range structure of glasses were studied. Density increases on average by about 0.5% to 1% and Tg values show drastic increase in the range of 8°C-64°C after annealing. Raman and FTIR studies were performed on glasses before and after annealing, FTIR studies found that bismuth borate glasses show a small but significant increase in the fraction of tetrahedral borons in the borate network with annealing. Raman studies on lead metasilicate glass showed an increase in the concentration of SiO4 units that contain three bridging oxygens. Raman and FTIR spectra of all annealed barium and lead tellurite glasses were indistinguishable from those of the initial samples, however the FTIR spectra of annealed 25MoO3-75TeO2 glass show changes in the relative intensities of the peaks due to MoO vibrations along with the growth and sharpening of low frequency Raman bands, furthermore this glass also showed large differences in its crystallization and melting properties during thermal analysis.