Ion transport mechanism in borate glasses: Influence of network structure on non-Arrhenius conductivity

In this paper, we report a non-Arrhenius behavior in the temperature-dependent dc conductivity of alkali ion conducting borate glasses below their glass transition. This behavior is strongly influenced by the alkali oxide content and by the type of the alkali ions, and is most pronounced in glasses with low alkali oxide content and with large alkali ions. In contrast to many fast ion conducting glasses, the curvature in the Arrhenius plot is positive. Furthermore, we show that annealing of the glass samples leads to a partial recovery of the Arrhenius behavior. Our experimental results are interpreted in terms of local structural changes in the borate network with temperature, which have been detected by means of solid state NMR spectroscopy.