Abstract
Nanoparticles of polycrystalline NiFe
2−
x
Cu
x
O
4 (0.0≤
x≤0.05) ferrites were prepared through the modified citrate-gel method. The samples were obtained as dried gel after the successful chemical reaction of their respective metal nitrate solutions in the midst of citric acid as catalyst. X-ray diffraction (XRD) and selective area electron diffraction (SAED) confirmed the single phase nature of all the samples with an average particle size of 19.8 (±1). Fourier transformation infrared spectroscopy (FTIR) shows the presence of two broad vibrational bands between 400 and 1000
cm
−1 corresponding to the tetrahedral and the octahedral sites. The variation of dielectric properties (
ε′,
ε″, tan
δ) and ac conductivity (
σ
ac), with frequency reveals that the dispersion is due to the Maxwell–Wagner type of interfacial polarization in general and due to hopping of charges between Fe
+2 and Fe
+3 as well as between Ni
+2 and Ni
+3 ions at B-sites. The complex impedance spectroscopy has been used to study the effect of grain and grain boundary on the electrical properties of all the ferrite nanoparticles.
► The paper discusses the effect of Cu doping on the structural and dielectric properties of NiFe
2O
4 spinel ferrite nanoparticles. ► The citrate gel method shows that the method has a good control over the size distribution, crystalline order and electrical properties. ► The dielectric properties of the NiFe
2−
x
Cu
x
O
4 show that these materials have promising applications in microwave dives.