Effect of compositional changes on the structure and properties of alkali-alumino borosilicate glasses

The effect of replacing BaO by SrO or Al2O3 by MgO on the structure and some physical properties of the glasses of the system Li2O-B2O3-(SrO)BaO-(MgO)Al2O3-SiO2-containing TiO2 have been investigated. Fourier transform infrared (FTIR) spectroscopy revealed that the addition of SrO at the expense of BaO gives no changes in the main structural building units. The addition of MgO instead of Al2O3 decreases the fraction of BO3 and increases the fraction of BO4 groups. Dilatometric measurements showed that the thermal expansion coefficients (alpha-values) were increased by gradual addition of SrO or MgO instead of BaO or Al2O3, respectively, however the transformation (T-g) and softening (T-s) temperature values of the glasses were decreased. The density was found to decrease as SrO/BaO or MgO/Al2O3 replacements increased. The conductivity, dielectric constant and dielectric loss (dielectric constant x loss tangent) of the glasses were investigated using the frequency response in the interval 200 Hz-100 KHz and the effect of compositional change on the measured properties was investigated. Measurements showed that the electric responses of samples were different and complex. The addition of SrO instead of BaO generally, increases the conductivity, dielectric constant and dielectric losss of the glasses. Increasing the MgO at the expense of Al2O3, the conductivity and dielectric constant of the glasses were decreased. However, the dielectric losss was increased. The electrical properties were found to be factors that are able to distinguish the various electrical parameters as a result of the change in composition. The obtained data were correlated to the internal structure of the glasses and the nature and role played by glass forming cations. (C) 2006 Springer Science+ Business Media, Inc.