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Glasses with compositions xBi 2 O 3 -(100 − x)B 2 O 3 with 30 x 60 mol% have been prepared using the normal melt quenching technique. Infrared (IR) spectroscopy was used as a structural probe of the nearest-neighbor environment in the glass network. Assessment of the thermal stability of these glasses was achieved in terms of various simple quantitative methods based on the characteristic temperatures, such as the glass transition temperature, T g , the onset temperature of crystallization, T in , the temperature corresponding to the maximum crystallization rate, T p , and the melting temperature, T m . In this case, k gl may be more suitable for estimating the glass thermal stability in the above composition range. In this work the kinetic parameter K r (T ) is added to the stability criteria. The thermal stability of the glasses that were studied has been correlated with the activation energy of crystallization by this kinetic criterion and compared with those evaluated by other criteria. The results of both the criteria and the kinetic parameter K r (T ) confirm that the thermal stability decreases with increasing Bi 2 O 3 content. The former parameters, besides the average force constant of the BO 3 structural unit, were characterized and discussed in terms of the changes in the glass structure.

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Glasses in the system Na2−2xB4−4xBixMo0.5xO7−4x, 0 ≤ x ≤ 0.4, have been prepared by the melt quenching technique. Elastic properties and IR spectroscopic studies have been employed to study the role of Bi2O3 and MoO3 on the structure of Na2B4O7 glass. Elastic properties and Debye temperature have been investigated using sound velocity measurements at 4 MHz. The results showed that the density and the molar volume increase while both sound velocities and the determined glass transition temperatures decrease with increase in x. Infrared spectra of the glasses reveal that the strong borate network consists of diborate units and is affected by the increase in the concentration of Bi2O3, and MoO3. These results are interpreted in terms of the increase in the number of non-bridging oxygen atoms, substitution of longer bond lengths of Bi–O, and Mo–O in place of shorter B–O bond and the change in Na+ ion concentration. The results indicate that bismuth and molybdenum ions have been substituted for boron ions as network modifier ions. The elastic moduli are observed to increase with the increase in Bi2O3 and MoO3 content. This contradiction in the elastic moduli–molar volume relation is attributed to the role of the respective bonds.