Tailoring the ferroelectric and magnetic properties of Bi₅Ti₃FeO₁₅ ceramics by doping with Co and Y

The ferroelectric and magnetic properties of four-layered Aurivillius Bi₅Ti₃FeO₁₅ (BFT) compounds via partial substitution of Bi³⁺ with Y³⁺ and Fe³⁺ with Co²⁺ (according to formula: Bi_5-xY_xTi₃FeO₁₅, x = 0.1, 0.2, 0.3; Bi₅Ti₃Fe_1-yCo_yO₁₅, y = 0.1, 0.3, 0.5) were investigated. Polycrystalline ceramics of Co and Y substituted BFT were prepared by conventional solid-state reaction. Crystal structure and phase purity were confirmed via X-ray diffraction and Rietveld refinement. Raman spectral signatures indicate that Y replaces Bi ions in the pseudo-perovskite layers and Co replaces Fe ions in the octahedral sites. SEM micrographs show a decrease in grain size for both chemically modified samples when compared to plate-like morphology for unmodified BFT with dimensions ranging from 3 to 5 μm in length and a thickness of ∼0.5 μm. The decrease in grain size is more pronounced in Co substituted samples with plate-like grain dimensions of 1 μm in length and 0.2 μm in thickness. Ferroelectric measurements show unsaturated leaky hysteresis loops in both chemically modified samples until the maximal applied electric field. Magnetic measurements confirm the paramagnetic nature of unmodified and Y substituted BFT ceramics while Co substituted BFT ceramics exhibit a typical ferromagnetic M-H loop. The largest remanent magnetization value of 0.084 emu/g at room temperature is recorded for the Co²⁺ substituted sample with x = 0.3.