Reversibly Strain Engineering and Electric-Field Control of Crystal Symmetry in Multiferroic Oxides

Multiferroic oxides, such as BiFeO3, have garnered significant attention due to their coupled ferroelectric, magnetic, and elastic properties, offering exciting opportunities for multifunctional device applications. Controlling phase transitions in these materials is critical for tuning their physical properties and achieving desired functionalities. While numerous studies have focused on ferroelectric-ferroelectric transitions at rhombohedral-tetragonal morphotropic phase boundaries, far less attention has been given to the ferroelectric-antiferroelectric phase boundaries. Such systems hold promise for discovering novel physical phenomena, such as reversible phase transitions, enhanced piezoelectricity, and magnetoelectric coupling. In this work, we report a reversible antiferroelectric-to-ferroelectric phase transition in La doped BiFeO3 thin films. By modulating the residual strain via film thickness, an antiferroelectric orthorhombic phase is stabilized within a ferroelectric rhombohedral phase matrix. Under an external electric field, the phase transitions reversibly between these two states. This discovery not only enriches the understanding of orthorhombic-rhombohedral morphotropic phase boundaries but also provides a potential pathway for developing magnetoelectric devices with enhanced functionality.