Structural, Morphological, Microstructural and Vibrational Characterization of Ni²⁺–La³⁺ Co-Doped CoFe₂O₄ Nanoferrites

AbstractNi²⁺ and La³⁺ co-doped CoFe₂O₄ nanoferrites using the formula Co₁₋ₓNiₓLaₓFe₂₋ₓO₄ (x = 0.00–0.25) was synthesized via thesol–gel auto-combustion technique to examine the effects of concurrent Ni²⁺ and La³⁺ inclusion on their structural andmorphological properties. The engineered nanoferrites were methodically analyzed using powder X-ray diffraction (P-XRD),Rietveld refinement, FESEM–EDS, TEM, HR-TEM, SAED, and FTIR spectroscopy. The P-XRD patterns validated theestablishment of a mostly single-phase cubic spinel structure, exhibiting distinctive reflections associated with the (111),(220), (311), (222), (400), (422), (511), (440), (533), and (444) planes. The crystallite dimensions diminished gradually from29.75 to 25.11 nm, and the lattice parameter reduced from 8.3820 to 8.3494 Å as the Ni–La concentration increased,signifying compositional alteration and localized lattice distortion. The volume of the unit cell diminished from 588.90 to582.0553 ų, while the X-ray density and porosity ascended from 5.345 to 5.4745 g cm⁻³ and from 56.18 to 65.732%,respectively. The specific surface area rose markedly from 11.8077 to 43.6445 m² g⁻¹, indicating the formation of a morerefined and porous nanostructure. Rietveld refinement additionally validated the appropriateness of the cubic Fd-3m spinelmodel, exhibiting satisfactory refinement reliability factors and goodness-of-fit metrics. FESEM and TEM analyzesdisclosed nanoscale particles exhibiting spherical to irregular shapes and considerable aggregation, with particle sizediminishing as Ni–La substitution increased. HR-TEM revealed distinct lattice fringes, while SAED patterns validated thepolycrystalline characteristics of the spinel phase. FTIR spectra displayed the distinctive metal–oxygen vibrations linked totetrahedral and octahedral positions, validating the retention of the spinel structure following co-doping. The findingsindicate that the concurrent substitution of Ni²⁺ and La³⁺ offers a viable method for modifying the crystal structure,microstructure, surface properties, and lattice vibrations of CoFe₂O₄ nanoferrites, underscoring their promise ascompositionally adjustable multifunctional ferrite materials