Piezoelectrics interconvert mechanical energy and electric charge and are widely used in actuators and sensors. The best performing materials are ferroelectrics at a morphotropic phase boundary, where several phases coexist. Switching between these phases by electric field produces a large electromechanical response. In ferroelectric BiFeO3, strain can create a morphotropic-phase-boundary-like phase mixture and thus generate large electric-field-dependent strains. However, this enhanced response occurs at localized, randomly positioned regions of the film. Here, we use epitaxial strain and orientation engineering in tandem—anisotropic epitaxy—to craft a low-symmetry phase of BiFeO3 that acts as a structural bridge between the rhombohedral-like and tetragonal-like polymorphs. Interferometric displacement sensor measurements reveal that this phase has an enhanced piezoelectric coefficient of ×2.4 compared with typical rhombohedral-like BiFeO3. Band-excitation frequency response measurements and first-principles calculations provide evidence that this phase undergoes a transition to the tetragonal-like polymorph under electric field, generating an enhanced piezoelectric response throughout the film and associated field-induced reversible strains. These results offer a route to engineer thin-film piezoelectrics with improved functionalities, with broader perspectives for other functional oxides.
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The data that support the findings of this study are available from the corresponding authors upon request.
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This research was partially supported by the Australian Research Council (ARC) Centre of Excellence in Future Low-Energy Electronics Technologies (project no. CE170100039) and funded by the Australian Government. D.S. and V.N. acknowledge the support of the ARC through Discovery grants. O.P. acknowledges the Australian Government Research Training Program Scholarship, the Australian Institute for Nuclear Science and Engineering (AINSE) post-graduate research award and the Scholarship AINSE Australian Nuclear Science and Technology Organisation (ANSTO) French Embassy programme. C.X. and L.B. acknowledge the Defense Advanced Research Projects Agency (DARPA) grant no. HR0011727183-D18AP00010 (Topological Excitations in Electronics (TEE) Program) and the Vannevar Bush Faculty Fellowship grant no. N00014-20-1-2834 from the US Department of Defense. X.C. acknowledges the use of facilities within the Monash Centre for Electron Microscopy, which were funded by ARC grants ARC Funding (LE0454166) and ARC Funding (LE0882821). The piezoresponse spectroscopy measurements were supported by the US Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division (K.P.K.) and performed at Oak Ridge National Laboratory’s Center for Nanophase Materials Sciences, which also provided support (R.K.V.), and is a US Department of Energy Office of Science User Facility. B.X. thanks the National Natural Science Foundation of China for financial support under grant no. 12074277 and the Natural Science Foundation of Jiangsu Province (BK20201404). We thank C. Paillard for fruitful discussions and for sharing his scripts, and L. Collins for assistance with the IDS measurements.
The authors declare no competing interests.
Peer review information Nature Materials thanks Kathrin Dörr, Sverre Selbach and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.
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Paull, O., Xu, C., Cheng, X. et al. Anisotropic epitaxial stabilization of a low-symmetry ferroelectric with enhanced electromechanical response. Nat. Mater. 21, 74–80 (2022). https://doi.org/10.1038/s41563-021-01098-w