Unveiling the relationship between packing fraction, elastic properties, and ionic conductivity in highly modified alkali-borate glasses

Abstract

The ionic conductivity of glasses can be understood through the Anderson and Stuart model, in which the process's activation energy is divided into two parts — the binding and the strain energies. In turn, the strain energy mostly depends on the glass's elastic properties, which can be related to the packing fraction according to the Makishima and Mackenzie model. In this work, the possible dependency between packing fractions, strain and ionic conductivity activation energies were studied for lithium and sodium borate glasses containing high alkali-oxide concentrations. A linear dependency was found for compositions up to ≈ 33 mol% alkali oxide, a composition known from the boron anomaly model. This result reinforces the strong electrolyte behavior of the glass up to ≈ 33 mol% concentration for both systems with an activation enthalpy of 0.6 eV while indicating a significant change in the charge carrier's behavior. Strain energy prediction fails for large amounts of alkali oxides, indicating other factors besides the elastic property are involved in the ionic conductivity of the highly modified glasses.