Dual-Site Mg²⁺ Substitution in LaFeO₃ ceramics: Defect Engineering and Multifunctional Property Modulation

Pristine LaFeO₃ and Mg²⁺-incorporated La-deficient LaFeO₃ (La₁₋ₓFeO3−δ:xMg, x = 0.2, 0.4) and Fe-deficient LaFeO₃ (LaFe₁₋ₓO3−δ:xMg, x = 0.2, 0.4) ceramics were synthesized from nanoparticles prepared via a low-temperature citrate sol-gel process. X-ray diffraction confirms the formation of a single-phase in pristine LaFeO₃, while minor secondary phases are observed in Mg²⁺-incorporated, La- and Fe-deficient compositions. Raman spectroscopy reveals distinct vibrational modes in Mg²⁺-incorporated La-deficient LaFeO₃, whereas Fe-deficient variants exhibit featureless spectra. Diffuse reflection spectral measurements show a direct bandgap of 2.15 eV and an indirect bandgap of 1.80 eV for pristine LaFeO₃, which narrows to 2.10 and 2.05 eV (direct) and 1.60 and 1.38 eV (indirect) upon Mg²⁺-incorporation in La-deficient LaFeO3. Conversely, Fe-deficient, Mg²⁺-incorporated LaFeO₃ exhibits broad absorption without a defined band-edge, suggesting the presence of defect states or mid-gap levels. Magnetic measurements at room temperature indicate a marked enhancement in magnetization (7.6 emu/g) in La-deficient compositions, indicative of emergent ferromagnetism, while Fe-deficient samples show weak ferromagnetism (1.2 emu/g), comparable to pristine LaFeO₃ (0.7 emu/g). O K-edge x-ray absorption spectroscopy reveals changes in Fe(3d)–O(2p), La(5d)–O(2p), and Fe(4sp)–O(2p) hybridizations. XANES analysis at the La L₃ and Fe K edges confirms the retention of La³⁺ and Fe³⁺ oxidation states. Local structural studies indicate site-specific Mg²⁺ substitution and the generation of oxygen vacancies, both of which critically influence the optical and magnetic properties. These results highlight the importance of defect engineering and local structural modulation in tuning the multifunctional properties of LaFeO₃-based perovskites.