Oxygen vacancies in BiFeO 3 thin films: formation mechanisms, regulation strategies and multifunctional properties

Bismuth ferrite (BFO) thin films are promising room-temperature single-phase multiferroics for information storage, sensing and optoelectronic applications. As the dominant intrinsic defects, oxygen vacancies are readily generated during thin-film growth, thermal processing, and aliovalent doping, and play a pivotal role in determining the structural, electrical, magnetic, and optical properties of BFO. This review summarizes recent advances in oxygen-vacancy engineering through elemental doping and thermal annealing, with emphasis on the regulation of vacancy concentration and spatial distribution and their impacts on crystal structure, ferroelectric domain evolution, and multifunctional properties. Challenges in the study of oxygen vacancies in bismuth ferrite are identified. Future perspectives are proposed to provide guidelines for the rational design of high-performance BFO-based multifunctional devices.