Stable ferroelectric domains with uncompensated bound charges in mixed-phase BiFeO3 films

The rapid development of artificial intelligence places high demands on memory devices with low power consumption, which drives the need for non-volatile ferroelectric memory. However, traditional views propose that the stability of ferroelectric polarization relies on screening the depolarization field, which constrains further device scaling. In this work, mixed-phase BiFeO3 thin films epitaxially grown on LaAlO3 substrates were investigated, where ferroelectric domains were directly observed and manipulated using atomic force microscopy. Piezoresponse force microscopy and Kelvin probe force microscopy results demonstrate that even under large depolarization fields, the domain structure with the morphotropic phase boundary (MPB) remains stable. Further analysis reveals that the MPB formation effectively tunes strain and polarization, thereby reducing strain and electrostatic energies. This indicates that the stability of ferroelectric polarization can be governed by the intrinsic structure. Our study reveals an “MPB-assisted polarization stabilization” mechanism, providing an experimental basis for state-of-the-art ferroelectric memory devices.