Rare Earth Substitution in Perovskite BiFeO₃ Multiferroic: Comparative Study of Structural, Magnetic, and Optical Properties

In this study, BiFeO₃ (BFO) and Er³⁺-, La³⁺-, and Nd³⁺-substituted BFO were synthesized using Pechini’s modified sol–gel auto-combustion route. Comprehensive investigations were conducted on the structural, magnetic, and optical properties of the samples. X-ray diffraction and Rietveld refinement analysis provided insights into the crystal structure, which was found to be distorted rhombohedral for all the samples except for BEFO (Bi_0.95Er_0.05FeO₃), which was orthorhombic. The crystallite size and strain were calculated by strain-size plots. Fourier transform infrared spectroscopy confirmed the crystallinity and characteristic FeO₆ peaks of perovskites in all the samples. Microstructural investigations using field-emission scanning electron microscopy imaging revealed the morphological features and particle size distribution. The magnetization–hysteresis (M–H) loop demonstrated that the M_s and M_r values decreased after the incorporation of rare earth (RE) ions in the BFO lattice, while electron paramagnetic resonance analysis elucidated the magnetic interactions within the materials. In addition, UV direct reflectance spectroscopy coupled with Kubelka–Munk plot analysis facilitated the determination of band gap energy values, which were in the range of 2.11–2.22 eV. The integration of these diverse characterization techniques offers a holistic understanding of the structural, morphological, magnetic, and optical properties of BFO and its RE-substituted variants. This multifaceted approach not only enriches our knowledge of these materials but also paves the way for their diverse applications in sensors, spintronics, actuators, and photocatalysts for environmental remediation.