Charge carrier concentration and mobility of ions in a silica glass

Abstract

Separate determination of the charge carrier concentration and the ionic mobility in glasses is difficult but useful in understanding the source of the conductivity variation in glasses with varying glass composition, cooling rates as well as temperatures. We suggest that the dielectric relaxation strength of the space charge polarization can be used to estimate the ionic charge carrier concentration and combining the result with dc conductivity, the ionic mobility can be determined. The method was used to determine the origin of the conductivity changes of a silica glass caused by fictive temperature change and water addition. We found that the observed conductivity decrease with increasing fictive temperature is due primarily to a decrease in mobility while the observed conductivity decrease with increasing water content is due primarily to a decrease in the charge carrier concentration.