Structural, optical, and electrical transport properties of some rare-earth-doped nickel ferrites: A study on effect of ionic radii of dopants

Abstract

Different rare-earth (Ho, Gd, Sm, Pr, and La)-doped nickel ferrites were prepared through the sol-gel citrate auto-combustion method. Rietveld refinement of the X-ray diffraction patterns confirmed the formation of an orthorhombic impurity phase for each doped sample. Structural parameters, including lattice parameter, crystallite size, microstrain, and different bond lengths, were calculated. Field emission scanning electron micrographs showed spherical grains and the existence of secondary phases for the doped samples. Elemental analysis of each component were performed using energy dispersive X-ray spectra. The shifting of the absorption bands of the Fourier transform infrared spectra depicted the rare earth-to-Fe substitution in octahedral sites of nickel ferrites. The optical band gap decreased with the smaller ionic radii of dopants. The study of ac and dc conductivity provided information about the conduction and dielectric relaxation mechanism and the effect of impurity phases. The electrical conductivity and dielectric study suggested that La- and Sm-doped samples showed the highest resistivity with high losses, whereas Ho- and Gd-doped samples showed moderate resistivity with minimum losses.