Enhanced piezoelectric response of the two-tetragonal-phase-coexisted BiFeO3 epitaxial film

A BiFeO3 epitaxial film composed of two tetragonal phases was deposited on SrTiO3 substrates by using oxygen-deficient La0.3Sr0.7MnO3−δ as the buffer. One of these phases is a high-temperature form of the highly elongated monoclinic type-C BiFeO3, and the other belongs to the strain-distorted version of the rhombohedral phase. The piezoelectric constant d33 of the mixed-phase structure was determined to be ~210 pm/V, much larger than that of the pure rhombohedral BiFeO3. Electric-field-induced strain up to 4% was observed, suggesting a strong electromechanical coupling of the film. These results enrich the knowledge on the strain-driven morphotropic phase boundary of BiFeO3, and thereby provide a possible way for future lead-free piezoelectric applications.