摘要
Understanding the elastic response on the nanoscale phase boundaries of multiferroics is an essential issue in order to explain their exotic behaviour. Mixed-phase BiFeO 3 films, epitaxially grown on LaAlO 3 (001) substrates, have been investigated by means of scanning probe microscopy to characterize the elastic and piezoelectric responses in the mixed-phase region of rhombohedral-like monoclinic (M I ) and tilted tetragonal-like monoclinic (M II,tilt ) phases. Ultrasonic force microscopy reveal that the regions with low/high stiffness values topologically coincide with the M I /M II,tilt phases. X-ray diffraction strain analysis confirms that the M I phase is more compliant than the M II,tilt one. Significantly, the correlation between elastic modulation and piezoresponse across the mixed-phase regions manifests that the flexoelectric effect results in the enhancement of the piezoresponse at the phase boundaries and in the M I regions. This accounts for the giant electromechanical effect in strained mixed-phase BiFeO 3 films.