GeO2-doped silica glasses:: an ac conductivity study

The dielectric response of (GeO2)(x)(SiO2)(1-x) glasses prepared from aerogels by means of a new sol-gel recipe has been studied by impedance spectroscopy. Ac conductivity measurements on silica glasses doped with GeO2 in the range 10(-3) -1 mol% have been carried out over six decades, in the range 0.1 Hz-100 kHz, for temperatures between 300 and 783 K. At sufficiently high temperatures, a dc conductivity plateau has been observed in the frequency range investigated. For the compositions considered in the present study, the dc conductivity and the corresponding activation energy seem to be only slightly influenced by the doping with GeO2. Sodium ion impurities, detected in these glasses in a concentration of several tens of ppm, are most likely responsible for the dc conduction process. Furthermore, the mean activation energy happens to increase as the temperature is decreased, suggesting a temperature dependence of the number of mobile defects. (C) 2002 Elsevier Science B.V. All rights reserved.