Frequency and temperature dependence of dielectric and electrical properties of TFe2O4 (T = Ni, Zn, Zn0.5Ni0.5) ferrite nanocrystals

Abstract

We have presented detailed dielectric and electrical studies of structurally characterized NiFe2O4, ZnFe2O4 and Zn0.5Ni0.5Fe2O4 nanoparticles, prepared through chemical ‘pyrophoric reaction’ technique. Dielectric constant study of those nanoparticles gives evidence of Maxwell–Wagner interfacial or space polarisation and dipolar polarisation in the samples. Dielectric constant is found to be the highest for ZnFe2O4 nanoparticles and gradually decreases with Ni doping, which has been explained considering the order of ionic polarizability of metal ions. Large dielectric loss value of NiFe2O4 compared to ZnFe2O4 and Zn0.5Ni0.5Fe2O4 nanoparticles imply more leakage current with increase in Ni content in the system. Furthermore, study of real part of complex impedance for ZnFe2O4 and Zn0.5Ni0.5Fe2O4 nanoparticles evidences low frequency sensitive interfacial polarisation of the system. Distinct signature of interfacial polarisation in both dielectric and complex impedance studies of those samples can be attributed to predominant interfacial effect due to their nanometric grain sizes. Complex impedance spectra have been fitted by parallel combination of grain boundaries resistance and capacitance circuit with varying temperatures. This also supports the dominating role of grain boundaries due to nanometric grain sizes of the samples. Activation energies have been estimated from both temperature dependent relaxation time and dc conductivity data, which indicates that same kinds of charge carriers are governing both the processes. Furthermore, from the analysis of ac conductivity as a function of temperature and frequency, the temperature activated electronic transport process has been attributed to large polaronic hopping in the system.