Dielectric Behavior of Lead-Silicate Glasses Containing Iron

The ac conductivity of lead-silicate glasses containing Fe was measured in the range 4.5° to 500° K to investigate the electronic hopping mechanism in these amorphous materials. Classes containing 0.0, 2.0, and 10.0 wt% Fe₂O₂ were prepared under normal atmospheric conditions. The ac conductivity, which increased with increasing Fe concentration, followed an Arrhenius expression at the higher temperatures. The activation energy for ac conduction increased with increasing Fe concentration, in contrast to the usual decrease in activation energy observed by other workers. The frequency of the conductivity σ (ω) was approximately of the form σ (ω)αω^-n where the exponent increases with increasing Fe concentration and temperature. This behavior is explained by assuming that a distribution of hopping distances and activation energies is involved in the ac electron transport mechanism. At low temperatures, the curves for tanδ vs T for all samples showed a broad relaxation peak at ∼ 70°K. Although this peak is frequency-dependent, it was independent of Fe concentration. The results did not indicate electron hopping between localized states in the temperature range studied.