Effect of Oxygen Vacancies on Dielectric, Magnetic and Optical Properties of Sm and Ti co-doped Bismuth Ferrite Ceramics with Morphotropic Phase Boundary

This study investigates the effect of oxygen vacancies on the dielectric, magnetic, and optical properties of Sm and Ti co-doped bismuth ferrite (Bi 0.85 Sm 0.15 Fe 0.97 Ti 0.03 O 3 ) ceramics, labeled as BSFO N (N 2 -sintered) and BSFO O (O 2 -sintered), which exhibited a morphotropic phase boundary (MPB). X-ray diffraction analysis, Rietveld refinement, and high-resolution transmission electron microscopy confirmed that the MPB structure, comprised polar rhombohedral ( R3c ), antipolar orthorhombic ( Pbam ), and nonpolar orthorhombic ( Pnma ) phases. The nonstoichiometric ratio from Rietveld refinement revealed higher oxygen vacancies and Bi decomposition in BSFO N ceramics. Scanning electron microscopy revealed larger grain sizes with small holes in BSFO N ceramics, while BSFO N ceramics displayed a dense, hole-free morphology. X-ray photoelectron spectroscopy further confirmed the presence of higher Fe 2+ oxidation states and increased oxygen vacancy formation in the BSFO N ceramics. The BSFO N ceramic exhibited a higher dielectric constant ( ) and higher dielectric loss ( ), both of which decreased with increasing frequency. In addition, the BSFO N ceramic displayed lower impedance, higher AC conductivity, and lower activation energy. The higher oxygen vacancies in BSFO N ceramics promoted ferromagnetism. Furthermore, BSFO N ceramics exhibited a slightly reduced optical bandgap ( = 2.063 eV) and a stronger second-harmonic generation response, confirming the effect of oxygen vacancies on the optical properties of Sm and Ti co-doped bismuth ferrite ceramics with an MPB.