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 x20Ag(2)O-(1-x)20Na(2)O-10Al(2)O(3)-7OSiO(2) in mol%, the conductivity, a, and its activation energy, E-sigma, 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 sigma=3.5 x 10(-5) S/cm at 200 degreesC, which was 1.5 orders of magnitude larger than that of initial glass. In the case of x25Ag(2)O-(1-x)25Na(2)O-25Al(2)O(3)-50SiO(2), the mixed mobile ion effect was also observed at x=0.5. The maximum conductivity of 2x10(-4) S/cm, at 200 degreesC was obtained in the fully ion-exchanged glass sample. The electric relaxation analysis was also conducted on both systems, and Kohlrausch-Williams-Watts (KWW) fractional exponent beta was obtained as a function of x. The decrease of beta was observed near x approximate to 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. (C) 2002 Elsevier Science B.V. All rights reserved.