Phase transitions in BiFeO3 nanoislands with enhanced electromechanical response

We propose a novel method to drive phase transitions by etching strained BiFeO3 thin films to nanoislands. Atomic force microscopy (AFM) measurements reveal that the amount of rhombohedral-like (R) phase increases as the BiFeO3 thin films with tetragonal-like (T) matrix are etched to nanoislands and larger fraction of R phase can be obtained with the size reduction from 1 μm to 200 nm, indicating the T to R phase transitions induced by partial release of substrate clamping. Using piezoresponse force microscopy (PFM), it is demonstrated that rhombohedral-like (R) to tetragonal-like (T) phase transitions can be reversibly achieved under DC electric field in BFO nanoislands. Large electromechanical response has been observed in BFO nanoislands as well. This approach can be extended to other strained oxide films and provide guidance for the development of high-performance electromechanical lead-free materials.