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Abstract

Electrical conductivity and dielectric measurements have been
performed for nanocrystalline NiFe2O4 spinel for four different
average grain sizes, ranging from 8 to 97 nm. The activation
energy for the grain and grain boundary conduction and its
variation with grain size have been reported in this paper. The
conduction mechanism is found to be due to the hopping of both
electrons and holes. The high-temperature conductivity shows a
change of slope at about 500 K for grain sizes of 8 and 12 nm
and this is attributed to the hole hopping in tetrahedral sites
of NiFe2O4. Since the activation energy for the dielectric
relaxation is found to be almost equal to that of the de
conductivity, the mechanism of electrical conduction must be
the same as that of the dielectric polarization. The real part
epsilon' of the dielectric constant and the dielectric loss
tandelta for the 8 and 12 nm grain size samples are about two
orders of magnitude smaller than those of the bulk NiFe2O4. The
anomalous frequency dependence of epsilon' has been explained
on the basis of hopping of both electrons and holes. The
electrical modulus analysis shows the non-Debye nature of the
nanocrystalline nickel ferrite.