Correlation between structural and dielectric properties of Ni-substituted magnetite nanoparticles

Nanocrystalline NixFe1−xFe2O4 (x = 0, 0.1, 0.2, 0.3 and 0.5) ferrite powder samples with particle size 8–16 nm are synthesized using the chemical co-precipitation method. X-ray diffraction pattern confirms the inverse spinel structure. The lattice constant of Ni-substituted samples is increased as compared to the pure sample, while particle size decreases continuously with increased Ni content. The increased lattice parameter is correlated to the change in cation distribution. The variation in dielectric constant and tan δ with frequency reveals that the dispersion is due to the Maxwell-Wagner type of interfacial polarization in accordance to Koop's phenomenological theory. p-type charge carriers are introduced due to the incorporation of Ni in magnetite nanoparticles. After T ∼ 250 K, the dielectric constant attains a maximum value with increasing temperature which is further followed by the decrement in dielectric constant due to p-type carriers. Change in lattice parameter with increasing Ni concentration and hopping at the O-site control ε′ for Ni-substituted magnetite nanoparticles. Dielectric constant is drastically enhanced by Ni substitution as compared to pure magnetite sample while the dielectric loss remains almost constant which explore these samples for potential applications in microwave absorbers