Room-temperature multiferroic enhancement in cobalt and iron co-doped Aurivillius ceramics via defect engineering strategy

Bi_3.25Nd_0.75Ti_3-x(Fe_0.50Co_0.50)_xO₁₂ ceramics (BNdT-FC_x) with 0≤x ≤ 0.30 were synthesized using the solid-state reaction method. The structural analysis confirmed the presence of the orthorhombic Bi₄Ti₃O₁₂ (BiT) phase, characterized by the space group B2cb. Rietveld refinement revealed pronounced octahedral distortions, particularly in the Ti(2)O₆ octahedra, which became more prominent with increasing Co (Cobalt) and Fe (Iron) co-doping levels. Dielectric measurements over the 300–1000 K temperature range exhibited significant low-frequency dielectric dispersion, attributed to increased localized charge carriers' contribution. Structural distortions strongly influenced the ferroelectric properties, specifically octahedral tilting and A-site ion displacement along the a-axis, which play a critical role in the polarization mechanism. The magnetic study indicated modest magnetic interactions in Nd-doped samples, whereas co-doping with Co³⁺/Fe³⁺ induced discernible ferromagnetic behavior, as evidenced by M-H hysteresis loops. Incorporating Co³⁺/Fe³⁺ co-dopants introduced oxygen vacancies, which correlated with a reduction in ferroelectric performance, likely due to domain pinning effects. This work provides comprehensive insights into the interplay between structural modifications and the resulting electrical and magnetic properties of BNdT-FC_x ceramics, highlighting their potential for advanced multifunctional material applications.