Leakage current and ferroelectric behavior of non-stoichiometric BiFeO3 thin films prepared at different atmospheres

Defect engineering in ferroelectric perovskites presents significant potential for the modulation of their properties. Hence, evaluating defect concentration is essential from the standpoint of defect regulation in ferroelectric perovskites. In the present work, a feasibility-extrapolated approach linking defects and conductivity was proposed in non-stoichiometric BiFeO3 thin films through leakage current/field strength (J/E) measurements under various atmospheric conditions. Specifically, the defect concentration can be indirectly estimated by measuring J/E, ensuring consistency with the calculations of defect concentration, conductivity, and J/E against oxygen partial pressure. Our findings indicate that the primary charge carriers in BiFeO3 thin films annealed in air are electrons (indicating n-type conduction), while those in O2-annealed condition are holes (reflecting weak p-type conduction). The concentrations of Bi and oxygen vacancies exhibit negative sensitivity to the Bi content but are independent of the atmospheric condition change from air to oxygen. Conversely, the concentration of Fe2+ increases with the increasing Bi content and slightly decreases when annealed atmosphere transfers from air to oxygen. Furthermore, the low-energy defect Bi center dot center dot Bi (resulting from the oxidation of BiXBi) plays an important role on the significant pinning strength, low breakdown field strength, and the unsaturation observed in the P-E loops for the currently investigated BiFeO3 thin films.