Phase separation in a glass melt with the composition 6.5Na2O · 33.5B2O3 · 60SiO2 studied by impedance spectroscopy

Abstract

Α glass with the composition 6.5Na2O · 33.5B2O3 · 60SiO2 was studied using impedance spectroscopy in the temperature range of 380 to 925 °C. In order to simulate the spectra obtained, simple equivalent circuits were used. At temperatures above a temperature, Tχ, below which phase separation occurs, the specific conductivities determined can be fitted to the Arrhenius equation. Below Tχ deviations from Arrhenius behaviour are observed, which are due to the formation of an Na2O and B2O3 rich phase with larger specific conductivity and an SiO2 rich phase with lower specific conductivity. The specific conductivities are smaller than expected from an extrapolation from temperatures > 750 °C. Within the temperature range of 700 to 520 °C, the slope in the Arrhenius plot becomes continuously more negative due to the change in the chemical compositions of the respective phases. At temperatures < 520 °C, the chemical compositions do not further change. Here again a constant slope in the Arrhenius plot is observed until it changes again at Tg.