ELECTRICAL-CONDUCTIVITY OF ZINC FERRITES NEAR STOICHIOMETRY AND MANGANESE ZINC FERRITES UNDER VACUUM OR IN THE PRESENCE OF OXYGEN

The electrical conductivity of zinc ferrites near stoichiometry and of manganese-zinc ferrites has been investigated as a function of temperature under vacuum and in the presence of oxygen. Under vacuum, the conductivity of these ferrites with iron excess is explained by the hopping mechanism, and with ZnO excess by the development of vacancies in octahedral sites of cation-deficient spinel. Activation energies and the transition temperatures are presented. During the oxidation in oxygen of Mn-Zn ferrites, the profile of the log sigma = f (T) curves shows that the mechanism of electrical conduction in the temperature range 100 to 350-degrees-C can be explained in terms of the oxidation of Fe2+ to Fe3+ ions at octahedral sites. For the temperature range 300 to 450-degrees-C, the conductivity involves the hopping of electrons from octahedral sites of Mn3+ ions to octahedral sites of Mn4+ ions. Above 550-degrees-C the oxidation of Mn2+ ions leads to a marked change in conductivity with the generation of new phases.