Ionic conduction and dielectric relaxation in Ag+/Na+ ion-exchanged aluminosilicate glasses: mixed mobile ion effect and KWW relaxation

Ag+/Na+ ion-exchanged aluminosilicate glasses with uniform concentration profiles were prepared, and their electrical conductivities were investigated as functions of the ion-exchange ratio and the initial glass compositions. In the case of the ion-exchanged glasses of x20Ag2O–(1−x)20Na2O–10Al2O3–70SiO2 in mol%, the conductivity, σ, and its activation energy, Eσ, showed a minimum and a maximum at the same ion-exchange ratio x=0.3, respectively, and the mixed mobile ion effect (MMIE) was observed. The fully ion-exchanged sample attained σ=3.5×10−5 S/cm at 200 °C, which was 1.5 orders of magnitude larger than that of initial glass. In the case of x25Ag2O–(1−x)25Na2O–25Al2O3–50SiO2, the mixed mobile ion effect was also observed at x=0.5. The maximum conductivity of 2×10−4 S/cm at 200 °C was obtained in the fully ion-exchanged glass sample. ectric relaxation analysis was also conducted on both systems, and Kohlrausch–Williams–Watts (KWW) fractional exponent β was obtained as a function of x. The decrease of β was observed near x≈0.3 in the former system, while that of the later system was independent of the ion-exchange ratio. Based on the structural analysis results, the observed behaviors were investigated from the point of view of the occupation of Ag+ ions on the non-bridging oxygen-site (NBO-site) and the charge compensation-site (CC-site) of AlO4 tetrahedral unit.