Influence of Nd3+ on Structural, Optical, Electrical, Dielectric, Magnetic, and NO2 Gas Sensing Properties of Nd3+ Substituted Ni–Cu Ferrites

Abstract

The Nd³⁺ substituted Ni–Cu ferrites having the general chemical composition of Ni_0.5Cu_0.5Nd_xFe_2–xO₄ (x = 0.1, 0.2, and 0.3) were synthesized by solid state reaction method. The XRD analysis revealed the confirmation and formation of cubic spinel structure of ferrites. The lattice parameter value varied from 8.318 to 8.343 Å. The lattice parameter and X-ray density were found to increase with increasing Nd³⁺ ion concentration due to higher ionic radius of Nd³⁺ ion. The SEM images illustrated that crystallite size decreases with increasing Nd³⁺ ion concentration due to unit cell growth and lattice distortion, which produces an internal stress preventing grain growth. From the FTIR spectra, the higher frequency band in the range of 500–600 cm^–1 confirmed the vibrations due to M–O stretching at the tetrahedral site, while the lower band in the range of 400–500 cm^–1 confirmed the movement of Fe⁺³–O^2– band group at the octahedral site. The higher the concentration of Nd³⁺ ions, the higher the resistivity of Nd-doped ferrites due to change in crystal structure and electronic configuration. For all Nd³⁺ doped samples, the dielectric constant and dielectric loss decreased with increasing frequency, representing the typical dielectric dispersion behaviour, and the AC conductivity increased. The optical band gap of Nd³⁺ substituted compounds were studied using UV-Vis spectrum. The absorbance wavelength of ferrites reduced with the substitution, the indirect band gap energy increased. When Nd³⁺ ions replaced Fe³⁺ ions on the tetrahedral B-site, the saturation magnetization increased. The coercivity decreased due to an increase in grain size which happens owing to substitution of Nd³⁺ ion. Gas sensing properties of Nd³⁺ doped ferrites were studied by using NO₂ gas. Sensitivity of ferrites was enhanced by Nd³⁺ doping via increasing the number of oxygen vacancies which improves the absorption of NO₂ gas.