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 Co/sub x/Fe/sub 3-x/O/sub 4/ (x=0.94, 0.97, 1.00, 1.03 and 1.06) under various heat-treatment conditions have been characterized, 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/sub gb/ in Fe-excess cobalt ferrites and R/sub g/ in Co-excess ones. It is verified that for the furnace-cooled Co/sub 0.94/Fe/sub 2.06/O/sub 4/, the conduction mechanism of the grain and grain-boundary is n-type and p-type, respectively. For furnace-cooled Co/sub 1.06/Fe/sub 1.94/O/sub 4/, 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.>