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.

Figure 1

Arrhenius plot of the dc conductivity (multiplied by the temperature) of $x{\mathrm{Na}}_2\mathrm{O}\bullet (1-x){\mathrm{B}}_2{\mathrm{O}}_3$ glasses with $0.10\le x\le 0.30$. The symbols represent experimental data points, while the solid lines are fits to an Arrhenius law.

Figure 2

The variation of the “apparent activation energy” with temperature in $x{\mathrm{Na}}_2\mathrm{O}\bullet (1-x){\mathrm{B}}_2{\mathrm{O}}_3$ glasses with $0.10\le x\le 0.30$.

Figure 3

Arrhenius plot of the dc conductivity (multiplied by the temperature) of $0.2M_2\mathrm{O}\bullet 0.8{\mathrm{B}}_2{\mathrm{O}}_3$ glasses with $M=\mathrm{Li}$, Na, K, Rb, and Cs. The symbols represent experimental data points, while the solid lines are fits to an Arrhenius law. The inset shows clearly that deviations from Arrhenius behavior are more pronounced in cesium borate glasses as compared to lithium borate glasses (for a given alkali oxide content).

Figure 4

Arrhenius plot of the dc conductivity (multiplied by the temperature) of a $0.1{\mathrm{Na}}_2\mathrm{O}\bullet 0.9{\mathrm{B}}_2{\mathrm{O}}_3$ glass sample with different thermal histories. The symbols represent experimental data points, while the solid lines are fits to an Arrhenius law.

Figure 5

Arrhenius plot of the dc conductivity (multiplied by the temperature) of a $0.3{\mathrm{Na}}_2\mathrm{O}\bullet 0.7{\mathrm{B}}_2{\mathrm{O}}_3$ glass sample with different thermal histories. The symbols represent experimental data points, while the solid lines are fits to an Arrhenius law.