Dual-site Mg2+ substitution in LaFeO3 ceramics: Defect engineering and multifunctional property modulation

Abstract

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.