Transient ionic conductivity in fused silica

Abstract

Transient currents in doped and commercial type-I fused silica glasses were monitored by electrolyzing alkali ions (Na+ , Li+ and K+) through a sample disk in a U-tube dc non-blocking conductivity cell until steady state was achieved. The experiments were carried out either at 600 or 650 °C. Approach to steady state varied from sample to sample depending not only on the electrolyzing ion but also on the alumina/alkali ratio and the concentration of Li+ and Na+ impurity level in the silica. Results indicated that the transient behavior (current versus time) at a particular temperature was best expressed as a lg — lg plot showing two linear regions. The initial slope was attributed to the flushing of more mobile species and the final slope to the disappearance of interdiffusional coupling effects. The nature of the interdiffusional coupling, in some cases, was typical of the mixed-alkali effect in silicate glasses containing much higher levels of mixed alkali.