Structural and Dielectric Behavior of Ca–Ni Ferrite Nanoparticles

ABSTRACT Calcium‐substituted nickel ferrite nanoparticles with composition Ca x Ni 1− x Fe 2 O 4 ( x = 0.1, 0.3, and 0.5) were synthesized using a sol–gel auto‐combustion method to examine the effect of Ca 2 + substitution on their structural, morphological, vibrational, optical, dielectric, and electrical properties. XRD confirmed the formation of a single‐phase cubic spinel structure with space group Fd3̅m for all compositions. A gradual shift of diffraction peaks toward lower angles and an increase in lattice parameter from 8.309 to 8.349 Å indicated lattice expansion due to the replacement of smaller Ni 2 + ions with larger Ca 2 + ions. The crystallite size, calculated using Scherrer, Williamson–Hall, and Rietveld refinement methods, increased from approximately 5 to 27 nm with increasing Ca concentration, while dislocation density decreased, suggesting improved crystallinity. Rietveld refinement also revealed an increase in unit cell volume, bond lengths, hopping lengths, and oxygen positional parameters, indicating lattice distortion and possible cation redistribution. FESEM shows nearly spherical nanoparticles, and EDX analysis confirmed the presence of Ca, Ni, Fe, and O without detectable impurities. Raman spectroscopy exhibited characteristic spinel ferrite vibrational modes ( A 1g , E g , and T 2g ), confirming phase formation and cation redistribution. UV–visible analysis revealed an increase in optical band gap with increasing Ca content, attributed to structural modification and quantum confinement effects. Dielectric studies showed strong frequency and temperature dependence, while electrical conductivity results indicated thermally activated hopping conduction involving electron and oxygen ion migration. These findings demonstrate that Ca 2 + substitution significantly tailors the structural and functional properties of NiFe 2 O 4 nanoparticles for potential electronic and dielectric applications.