Revealing the interplay of structural phase transitions and ferroelectric switching in mixed phase BiFeO3

Epitaxially strained BiFeO3 thin films with co-existing tetragonal- and rhombohedral-like phases exhibit a range of intriguing functional properties, often strongly related to the unique microstructure of the film. Here we report enhancements in electromechanical response during simultaneous nanoscale application of electric field and localised stress. These enhancements manifest in the form of peaks, or humps, in the piezoresponse hysteresis loops obtained under select polarity of applied electric field, corresponding nominally to a downward polarisation. Using a variation of band excitation piezoresponse force spectroscopy to collect electromechanical hysteresis loops and to simultaneously monitor the elastic behaviour during switching, we develop a comprehensive picture of the complex interplay of ferroelastic structural transitions and ferroelectric switching and its impact on the overall functional response. Such an understanding is a crucial step towards realising practical electronic devices, such as pressure sensors, incorporating this promising material.