The internal friction of lithium and sodium borophosphate glasses

Alkali borophosphate glasses have recently gained strong interest, not only for their fundamental importance due to the mixed glass former effect but also because of their potential applicability as solid state electrolytes in energy harvesting devices. In the present work, internal friction measurements of lithium and sodium borophosphate glasses have been performed in order to look for further insights on the relationships between the ionic conduction mechanism and the structure of the glasses that has been previously determined. Absorption of acoustic waves shows two marked internal friction peaks with activation energy in the range of the activation energy for the ionic conduction of the glasses between 0.5 and 0.7 eV. Furthermore, the substitution of phosphorus by boron network former results in the decrease of the activation energy associated to both processes in parallel to the Ea of the ionic conduction of alkali cations; and the relationship between the areas of both peaks suggests a change of the distribution of alkali ions between positions energetically different in agreement with the structural changes of the glass network.