ANOMALOUS DC RESISTIVITY AND DIELECTRIC BEHAVIOR IN MN SUBSTITUTED NI-ZN FERRITES

The anomalous electrical behaviour of dc resistivity as a function of temperature for Mn substituted Ni-Zn ferrites with general formula Zn0.3Ni0.7+xMnx Fe2-2xO4 has been studied. At lower Mn concentrations, the increase in dc resistivity is attributed to the hindering of Verwey mechanism between Fe2+ reversible Fe3+ ions. The decrease in resistivity at higher Mn concentrations with x > 0.15 is attributed to the formation of Mn3+ cluster, Mn2O3 phase and Ni2+ --> Ni3+. The scanning electron micrographs support the existence of impurity phase at higher concentrations of Mn. The activation energy values show one to one correspondence with resistivity values. The dispersion of dielectric constant is explained on the basis of interfacial polarization. However, compositional variation of dielectric constant and loss tangent have shown two regions, one for x less-than-or-equal-to 0.15 in which the behaviour of dielectric is as usual and the other for x > 0. 1 5 for which the nature of dielectric is complex. The complex dielectric structure might have its origin in different valence states of Mn, inhomogeneities within the ferrite grain, oxygen stoichiometry and formation of Mn2O3.