Dielectric, impedance, and modulus spectroscopic studies of lanthanum-doped nickel spinel ferrites NiLaxFe2-xO4 nanoparticles

A series of lanthanum (La)-doped nickel (Ni) ferrites NiLaxFe2-xO4 with doping concentrations (x = 0.0, 0.01, 0.02, 0.03, 0.04, and 0.05) is synthesized via a sol–gel auto-combustion method. Structural properties are determined with the help of X-ray diffraction (XRD). The effect of La doping on dielectric properties of Ni ferrites is discussed. XRD analysis confirms the existence of pure FCC spinel phase, and no impurity phase was detected. The lattice constant decreases initially due to strain produced by La3+ ions replacement. At higher doping concentrations, the lattice constant increases due to the large ionic radius of La3+ as compared to Fe3+. Tangent loss (tanδ), dielectric constant, and dielectric loss values are determined in the 1 MHz to 3 GHz frequency range, and explained by the Maxwell–Wagner model. A persistent behavior of dielectric loss and dielectric constant was found in the mid microwave frequency region. The most stable behavior of the dielectric constant (ε′) and dielectric loss (ε″) in the high-frequency region is found with (x = 0.04). Ac conductivity is also discussed in the 1 MHz to 3 GHz region, and is found to be impacted by grain and grain boundary resistive behavior at low and high frequencies. Cole–Cole plots of different samples, corresponding to different doping concentrations, are used to describe the conduction phenomena. The stable response of dielectric constant (ε′) and dielectric loss (ε″) in the mid microwave frequency region makes NiLaxFe2-xO4 nanoparticles a potential candidate for microwave devices.