Influence of bismuth doping on structural, electrical and dielectric properties of Ni–Zn nanoferrites

Abstract

Bismuth doped Ni–Zn ferrites of the composition Ni0.5Zn0.5BixFe2-xO4 with (x = 0.00, 0.02, 0.04, 0.06, 0.08, 0.1) have been synthesized by a citrate precursor method. Bismuth was doped to tailor the properties of Ni–Zn spinel ferrite. X-Ray Diffraction (XRD) data was used to calculate lattice parameter, density, porosity and hopping length values which revealed that all annealed bismuth doped nickel zinc nanoferrites display a single phase cubic spinel structures. Average crystallite size was found to be in the range of 15–28 nm. Williamson-Hall method was used to deduce the average lattice strain experienced by the nanocrystalline. A tensile strain was observed with an increase in the bismuth concentration from x = 0.00 to x = 0.04 which leads to an expansion of lattice while a compressive lattice strain was observed for the concentration x = 0.06 due to contraction of the lattice. Fourier Transform Infra Red (FTIR) peaks confirmed the appearance of absorption bands at a wave number 405 cm−1 and at a wave number 580 cm−1 confirming tetrahedral and octahedral modes of vibrations respectively. I–V characteristics at 4 V voltage were studied at room temperature. A highly resistive behaviour of the samples of the order of 1010 Ω-cm was observed making these materials suitable for high frequency applications. The investigations on real part, imaginary part of dielectric constant and dielectric loss tangent were carried out in the frequency range 10 kHz to 10 MHz at room temperature. Dielectric behaviour showed that with an increase in concentration of bismuth, the value of real part of dielectric constant increases from 5.161 to 11.162 at 104 Hz frequency and the value of dielectric loss tangent decreases from 0.79 to 0.33. AC conductivity of all the samples was found to increase with an increase in frequency which is explained on the basis of Koop's Phenomenological theory.