Dispersion observed in electrical properties of titanium-substituted lithium ferrites

Abstract

The current-voltage characteristic of polycrystalline titanium-substituted lithium ferrites has been measured at temperatures above room temperature. At voltages below a critical value an Ohmic relationship is observed, while it obeys a power-law relationship (i∝Vα, where α is a temperature-dependent constant) above the critical voltage. At low voltages conduction is determined by the boundary layer, whereas at higher voltages, the current in the solid is mainly due to the space-charge-limited carriers. ac conductivity (σac) and dielectric permittivity (ε') show a large temperature-dependent dispersion in the 5-10-MHz range. The experimental results indicate that titanium substitution suppresses all these parameters. The dielectric relaxation has a very large relaxation intensity. In the theoretical model the temperature- and frequency-dependent layer properties are inserted into Koop's model and the theoretical dispersion curves are obtained. The agreement of these data with the experimental findings is remarkable.