Influence of Cerium (Ce3+) Substitution on the Structural and Frequency-Dependent Electrical Properties of Co0.9Fe2.1-xCexO4 Nanoferrites

This study investigates the impact of rare-earth cerium (Ce³⁺) substitution on the structural and electrical properties of cobalt-rich nanoferrites. A series of nanoparticles with the nominal composition Co_0.9Fe_2.1-xCe_xO₄ (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 Ce³⁺ 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 Fe³⁺ ions by Ce³⁺ ions at the octahedral sites, which limits the hopping mechanism between Fe²⁺ and Fe³⁺ ions. The significant reduction in dielectric loss highlights the potential of these cerium-doped nanoferrites for high-frequency device applications.