Critical transition of conductance and dielectric relaxation of synthesized fused silica investigated by electrical impedance spectroscopy

• A.C. electric impedance of synthesized fused silica is measured at temperatures between 250 °C and 700 °С.
• Critical transition is observed in temperature-dependent conductivity and relaxation of synthesized fused silica at around 500 °C.
• Occurrence of the critical transition correlates to the heterogeneous crystallite domains existing in synthesized fused silica.

In this work, a critical transition at about 500 °C in alternate-current (a.c.) conductance and dielectric relaxation of synthesized fused silica is first observed. The synthesized fused silica sample demonstrates the features of high hydroxyl content and low metal impurities through infrared absorption and ultraviolet transmittance analyses. The dispersion profiles of conductivity at different temperatures demonstrate the feature of the thermally-activated, long-range conduction. Besides, the temperature dependence of a.c. conductivity and dielectric relaxation shows different behaviors in high or low temperature range, thus lead to a critical transition occurring around 500 °C. It is believed that the occurrence of the critical transition is ascribed to the heterogeneous crystallite domains, which go through a transformation of stacking structure when the sample was subjected upon a heating.