Effect of single point defect on local properties in BiFeO ₃ thin film

Point defects commonly exist in artificially prepared ferroelectric oxide films. Here, the local polarization characteristics around a single point defect of Bi substitution in the Fe sites (antisite Bi, Bi _Fe ) in BiFeO ₃ (BFO) thin film, are studied at an atomic scale. Both first-principles theory and atomically resolved scanning transmission electron microscopy images show that a single point defect expands the lattice (∼2.4% in-plane direction and 0.8% along out-of-plane direction) but suppresses the surrounding polarization by more than ∼27%. The suppression of polarization is due to the formation of a single unit cell of non-ferroelectric Bi ₂ O ₃ , across which the accumulation of polarization bound charge induces a strong depolarization field. Therefore, structure relaxation makes the Bi ₂ O ₃ coherently polarized and meanwhile suppresses the surrounding polarization. Such point defects act as a pinning center to domain wall motion, which gives rise to incomplete switching, fatigue, and aging of ferroelectric devices.