Ion conduction in beryllium-alumino-silicate glasses doped with sodium or sodium and lithium ions

Electrical properties of beryllium-alumino-silicate glasses containing sodium ions or sodium and lithium ions were studied with impedance spectroscopy technique over a frequency range from 10 mHz to 1 MHz and at temperature range from 213 to 473 K. The frequency- and temperature-dependent conductivity spectra of individual single alkali glasses were superimposed by means of the Summerfield scaling. Mixed-alkali glasses do not overlap into a single master curve. Glasses doped with sodium ions exhibit significantly higher values of D.C. conductivity and lower activation energy (similar to 0.63 eV) than glasses doped with both sodium and lithium ions (similar to 0.95 eV). The observed mixed-alkali effect can be described by the dynamic structure model (DSM). The conductivity pre-exponential factors and activation energy follow the Meyer-Neldel rule in both glass series. It was observed that the replacement of SiO2 by BeO in single cation glasses resulted in decrease in activation energy and pre-exponential factor sigma(0). In mixed cations glasses similar effect found for D.C. conduction process parameters was assigned to influence of both oxides BeO and Al2O3.