Influence of Dual Cationic Substitution on the Structural and Optical Behavior of Nano-Ferrites

This study investigates the structural and optical modifications induced by dual cationic substitution in Ca0.2ZnxCo0.8−xFe2O4 nano-ferrites, synthesised via a sol–gel auto-combustion route for compositions where x = 0.1, 0.3, 0.7, and 0.8. The synthesis method ensured uniform distribution of precursor ions and precise stoichiometric control, yielding nanoscale ferrites with tailored properties. X-ray diffraction (XRD) analysis confirmed the formation of a single-phase cubic spinel structure across all samples, with no secondary phases. Crystallite sizes, calculated using the Scherrer formula, ranged from 12 to 50nm, affirming the nanocrystalline nature of the materials. UV–Visible spectroscopy revealed composition-dependent variations in optical absorption, with band gap energies ranging from 1.69 to 1.96 eV. These changes are attributed to the redistribution of Zn2+ and Co2+ ions between tetrahedral and octahedral sites, which modulate Fe–O–Fe and Fe–O–M (M = Zn, Co) super exchange interactions and alter the electronic density of states near the Fermi level. The findings demonstrate that co-substitution of Zn and Co in Ca-ferrites offers a viable route for engineering band structure and crystallinity, with potential applications in optoelectronic devices and photocatalysis.