Conductivity behavior of n-type semiconducting ferrites from hydrothermal powders

The frequency and temperature dependencies of the dielectric permittivity and of the electrical conductivity of excess ferrous ions hydrothermal NiZn ferrites were analyzed before and after sintering. A decreasing tendency with frequency of the dielectric responses was observed, but the high permittivities attained (ε′ ≈ 10⁵) masked any relaxation in these materials. This behavior is characteristic of n-type semiconducting ferrites, where electron hopping between Fe⁺² and Fe⁺³ ions leads to very high conductivity values. The temperature dependence of the dielectric permittivities revealed the existence of broader peaks. The electron hopping mechanism leads to a frequency dispersion of the temperature where the permittivities attain their maxima. The electrical conductivity variations with temperature exhibited Arrhenius-type behaviors, with activation energies ranging from 0.34 eV (hydrothermal powder) to 0.16 eV (for the highest sintering temperature). These results were correlated to the variations in Fe⁺² concentration and microstructure.