Structure, Morphology, DC-Electrical and Dielectric Characteristics of Chromium(III) Substituted Co-Li Ferrite Nanoparticles

In this study, a detailed analysis of the lattice structure, micro-structural features, DC-electrical properties and dielectric characteristics of Cr3+-substituted cobalt-lithium-based ferrite oxide nanoparticles (CoLiFCr NPs) synthesized using a sol-gel method enhanced by synergistic sol-gel auto-combustion is presented. Citric acid monohydrate (C6H8O7·H2O) was utilized as a chelating agent, maintaining a metal nitrate to citrate ratio of 1:3. Substituting Cr3+ in Co-Li ferrite significantly alters its crystal structure, morphological, DC-electrical and dielectric characteristics. The X-ray diffraction (XRD) analysis confirmed the crystalline formation of Co0.8Li0.4Fe2-xCrxO4 nanoparticles (where x = 0.0, 0.2, 0.4 and 0.6); exhibiting the single-phase cubic structure characterized by a spinel configuration, falling under the space group Fd-3mO7h. The lattice constant a for CoLiFCr NPs (x = 0) was measured at 8.338 ± 0.002 Å, which decreased to 8.291 ± 0.002 Å upon Cr substitution (x = 0.6), as confirmed by Cohen’s analytical graphs. The crystallite size (D), determined using the Debye-Scherrer’s formula, ranged from around 18.9 to 29.74 nm. Peak broadening in CoLiFCr NPs was further examined through Williamson-Hall and size strain analyses. The FTIR spectra of CoLiFCr nanoparticles revealed the presence of metal-oxygen (M-O) bonds typical of spinel structures, featuring significant peaks at 443 cm–1 and 537 cm–1. High-resolution transmission electron microscopy (HR-TEM) images showed the single-crystal CoLiFCr NPs with nearly spherical morphologies. The study of optical properties was conducted using UV-visible spectroscopy. The nanoparticles with x = 0.2 displayed high ε' values at 50 Hz, indicating strong polarization capabilities, while those with x = 0.6 exhibited a decrease possibly linked to structural changes affecting polarization. The DC resistivity of CoLiFCr nanoparticles was investigated to understand their electrical behaviour highlighting the influence of substitution of Cr3+ on conductivity.