INFLUENCE OF HEAT-TREATMENT CONDITIONS ON THE ELECTRICAL-CONDUCTION MECHANISM OF GRAIN-BOUNDARY IN COBALT FERRITES

The electrical resistance and conduction mechanism of the grain-boundary in CoxFe3-O-x(4) (x = 0.94, 0.97, 1.00, 1.03 and 1.06) under various heat-treatment conditions have been chracterized, using a complex impedance analysis technique. The electrical resistance of cobalt ferrites decreases with increasing quenching temperature which is mainly attributed to the decrease of R(g.b) in Fe-excess cobalt ferrites and R(g) in Co-excess ones. It is verified that for the furnace-cooled Co0.94Fe2.06O4 the conduction mechanism of the grain and grain-boundary is n-type and p-type, respectively. For furnace-cooled Co1.06Fe1.94O4, the conduction mechanism of the grain and grain-boundary is p-type and n-type respectively. These results indicate that the resistivity in the p-type part of cobalt ferrites decreases more rapidly than that in the n-type part with increasing quenching temperature The conduction mechanism of the grain-boundary is discussed to relate to the preferential oxidation of cations and the disorder near and at the grain-boundary