Dielectric relaxation in iron-containing borate glasses

The ac and dc conductivities, dielectric constant and dielectric loss of a series of calcium borate glasses containing Fe2O3 up to 10 mol% were measured as a function of temperature (300-700 K) and frequency (102-105 c/s). Glasses melted in platinum crucibles were found to show slightly higher dielectric constants and conductivities than glasses melted in zirconia crucibles under the same melting conditions. Relaxation effects with a distribution of relaxation times were observed for all the glasses of this system. The data show that the pre-exponential factor τ0 is about 10-11 s. Peaks in tan δ were found to shift to higher temperatures when the frequency of measurements was increased. Activation energy for dc conduction was found to be equal to that of ac conduction. No polarization effects were observed in these glasses, indicating that conduction is predominantly electronic.