Effect of physical aging on ionic conductivity of network oxide glasses

This study investigates the effect of α-relaxation induced by physical aging due to a down-jump in fictive temperature (T_f) on the alkali ion hopping dynamics and the resulting ionic conductivity in different network oxide glass-forming systems. Electrochemical impedance spectroscopy, differential scanning calorimetry, and density measurements were used to analyze this effect. Results from ex situ and in situ aging experiments show excellent agreement and demonstrate that α-relaxation during aging significantly reduces the ionic conductivity of the glass as its density increases and T_f decreases. In single-alkali Li disilicate and Li metaphosphate glasses, the migration enthalpy $\Delta H_m$$\Delta H_m$ of ionic conduction remains constant after aging, while the migration entropy $\Delta S_m$$\Delta S_m$ decreases, leading to a corresponding reduction in the hopping rate of mobile alkali ions. In contrast, in the mixed-modifier Na-Mg metaphosphate glass, both $\Delta H_m$$\Delta H_m$ and $\Delta S_m$$\Delta S_m$ increase after aging. This behavior is potentially explained by a spatial redistribution of Na and Mg cations likely occurring alongside α-relaxation during aging. The findings suggest that significant increases in the ionic conductivity of a glass, even by orders of magnitude, can be achieved by raising its T_f. This implies that fast-quenched glass products, such as thin films or fibers, may have novel applications as sensors and solid electrolytes.