Influence of Cerium (Ce³⁺) Substitution on the Structural and Frequency‐Dependent Electrical Properties of Co_0.9Fe_2.1‐<i>_x</i>Ce<i>_x</i>O₄ Nanoferrites

Abstract This study investigates the impact of rare‐earth cerium (Ce 3+ ) substitution on the structural and electrical properties of cobalt‐rich nanoferrites. A series of nanoparticles with the nominal composition Co 0.9 Fe 2.1‐ x Ce x O 4 (where x = 0.0, 0.025, 0.05, 0.075, and 0.1) are synthesized via the sol‐gel auto‐combustion method. X‐ray diffraction (XRD) analysis confirms the formation of a single‐phase cubic spinel structure for all compositions, with the lattice parameter systematically increasing from 8.38 to 8.42 Å with rising cerium content, indicating the successful incorporation of the larger Ce 3+ ions into the lattice. The crystallite size, estimated using the Debye‐Scherrer formula, is found to be in the nanometer range. Electron microscopy studies (SEM and TEM) reveal agglomerated, quasi‐spherical nanoparticles. The frequency‐dependent electrical properties are analyzed at room temperature. Results show a systematic decrease in AC conductivity, dielectric constant (ε'), and dielectric loss tangent (tan δ) with increasing cerium concentration. This behavior is attributed to the substitution of Fe 3+ ions by Ce 3+ ions at the octahedral sites, which limits the hopping mechanism between Fe 2+ and Fe 3+ ions. The significant reduction in dielectric loss highlights the potential of these cerium‐doped nanoferrites for high‐frequency device applications.