Electrical and dielectric relaxation in silica glasses at low temperature

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Electrical and dielectric relaxation were studied for 5 types of silica glasses. Measurements were carried out mainly by the dc charging-discharging method under a metal blocking electrode. The effect of sample thickness on relaxation was measured to distinguish bulk conductivity from surface effects and results were compared with ac impedance measurements. It is shown for type III and IV silica glasses that there is an additional relaxation after the conduction relaxation. This relaxation, which termed relaxation II, showed sample thickness dependency, indicating that it originates at the surface of sample. However, type I and type II silica glass did not show relaxation II in the same time range. To explain the different relaxation behavior of various types of silica glasses, a theoretical model for space charge polarization was applied to the present results. It was found that the dielectric and electrical relaxation by space charge polarization are functions of (i) sample thickness, (ii) charge carrier concentration, (iii) charge carrier mobility, and (iv) blocking condition of the electrodes. Space charge polarization theory successfully explains sample thickness dependency and different relaxation behavior of the silica glasses in the present work. Differences in relaxation behavior are due to differences in material parameters that are controlling the space charge polarization process.