Tailoring structural, electrical, and magnetoelectric properties of BiFeO3 ceramics via low-level cobalt substitution

This study presents a comprehensive investigation of the structural, microstructural, electrical, magnetic, and magnetoelectric properties of low-level substitution of Co 3+ for Fe 3+ ions in the perovskite B-site of BiFeO 3 (BiFe 1 −x Co x O 3 , x = 0.01, 0.015 and 0.02). X-ray diffraction combined with Rietveld refinement confirms the retention of the rhombohedral R 3 c structure across all compositions, with a systematic contraction of the lattice parameters attributed to the smaller ionic radius of Co 3+ compared to Fe 3+ . Microstructural analysis revealaled a doping-induced evolution from heterogeneous grain growth and high microstrain at intermediate doping levels to a more refined and compact microstructure at 2.0 at.%, suggesting the presence of stress relaxation mechanisms. Electrical measurements demonstrated that cobalt doping significantly modulated resistivity and time stability, with the 2.0 at.% sample exhibiting enhanced stability and lower resistivity due to improved charge transport pathways. Dielectric analysis indicates a trade-off between permittivity and losses: while low doping favors dielectric stability with minimal conduction losses, higher cobalt content enhances permittivity at the expense of increased dielectric losses driven by defect-mediated hopping conduction. Magnetic characterization reveals a progressive collapse of the cycloidal spin structure, resulting in enhanced remanent magnetization, coercivity, Rayleigh nonlinearity, and magnetic energy dissipation. Magnetoelectric coupling exhibited a strong dependence on doping levels, with robust intrinsic coupling at x = 0.01 transitioning to defect-driven extrinsic behavior at higher concentrations. Notably, the strongest and most symmetric magnetoelectric response is observed at x = 0.01, indicating that low-level Co substitution is sufficient to suppress the cycloidal spin structure while preserving high electrical resistivity and intrinsic coupling mechanisms. Higher Co concentrations, although enhancing magnetic irreversibility, introduce defect-driven conduction and extrinsic effects that deteriorate the magnetoelectric performance. These findings establish cobalt substitution as an effective strategy for tailoring the multifunctional properties of BiFeO 3 , providing key insights into the interplay between structural distortions, defect chemistry, and functional performance in multiferroic perovskite systems. • Low-level substitution of Co 3+ for Fe 3+ ions in the perovskite B-site preserves the R 3 c symmetry in BiFeO 3 ceramics • Substitution modulates microstructure, resistivity, and dielectric response • Magnetoelectric coupling shifts from intrinsic to extrinsic with Co substitution at the Fe site