High temperature impedance spectroscopy of homogeneous and phase separated melts and glasses of the composition 48.5SiO2 · 48.5B2O3 · 3Na2O

A glass with the composition 48.5SiO2 · 48.5B2O3 · 3Na2O was studied at temperatures in the range from 340 to 860 °C using impedance spectroscopy. The spectra obtained were simulated using a simple equivalent circuit. During cooling of a sample, the specific conductivity of the sample decreased according to Arrhenius equation until at temperatures <670 °C phase separation occurs (droplet phase: Na2O/B2O3-rich) which runs parallel to deviations from linearity in the Arrhenius plot. In the temperature range from 670 to 630 °C, specific conductivities at constant temperature depend on time due to decreasing Na2O concentrations in the matrix during cooling and increasing Na2O-concentrations during heating. The specific conductivities during heating and cooling exhibit a hysteresis which is explained by changes in the chemical compositions of matrix and droplet phase during thermal treatment which, however, always deviate from the equilibrium concentrations at temperatures <670 °C.