Ionic Conductivity in Fused Silica: II, Steady‐State Behavior

Abstract

Direct‐current ionic conductivity measurements on type‐I doped fused silica glasses were carried out in blocking and nonblocking modes between 300° and 800°C. The analysis of conductivity in steady state showed that the behavior was non‐Arrhenius in nature and that In (conductivity) followed a second‐degree polynomial of 1/ T. The normalized conductivity for Li + and Na + ions at a particular temperature increased with the alumina/alkali ratio up to about 8 and appeared to level thereafter. This trend was similar to that observed for viscosity in the same glasses published by Bihuniak et al. 1 For K + electrolysis, no significant trends in the normalized conductivity versus alumina/alkali ratio could be observed. The presence of nonlinearity in Arrhenius behavior could be ascribed to the combined effect of two types of sites present in fused silica: SiO − and AIO 4 − sites, where the AIO 4 − sites presumably have a lower binding energy for the Li + Na + , and K + ions than do the SiO − sites. It is argued that, unlike alkali aluminosilicates, the SiO − sites in fused silica do not disappear at an alumina/alkali ratio of 1, and only reach a sturation level at a ratio of about 8, a conclusion also reached by Bihuniak et al. 2 using randomwalk simulation.