Effect of Single Point Defect on Local Properties in BiFeO ₃ Thin Film

Abstract

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, BiFe) in BiFeO₃ (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 Bi2O3, across which the accumulation of polarization bound charge induces a strong depolarization field. Therefore, structure relaxation makes the Bi₂O₃ 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, fragility, and aging of ferroelectric devices.

Keywords: Ferroelectric, point defect, scanning transmission electron microscopy, quantitative image analysis, density function calculations