Electric control of oxygen vacancies in homo-ferroelectric-domain BiFeO₃

Although the performance of BiFeO₃ (BFO) films has been extensively and deeply studied, further exploration is still needed to understand the correlation between a ferroelectric single domain and high performance in BFO single crystals. Therefore, we conduct the biased in situ transmission electron microscopy experiments on the electrical transport properties of BFO single crystals with single domains. The in situ measured I-V curves indicate neither one-way conduction nor resistance switching. The conductive behavior of BFO corresponds to space charge-limited conduction, indicating a high concentration of oxygen vacancies and the presence of Ohmic contact between the Pt electrode and BFO. After applying a DC constant voltage, the resistance decreases by approximately 50% and partially recovers after exposure to air. The electron energy loss spectroscopy spectra under different conditions indicate that BFO interacts with the external environment. Specifically, DC voltage causes BFO to release oxygen atoms, resulting in an increase in oxygen vacancy concentration and decrease in resistance. Air oxidation leads to a decrease in oxygen vacancy concentration and partial recovery of resistance. In addition, in situ heating experiments (at 20-400 °C) indicate that oxygen vacancies mainly originate from the external electric field rather than thermal effects.