Giant Superelastic Piezoelectricity in Flexible Ferroelectric BaTiO₃ Membranes

Abstract

Mechanical displacement in commonly used piezoelectric materials is typically restricted to linear or biaxial in nature and to a few percent of the material dimensions. Here, we show that free-standing BaTiO3 membranes exhibit non-conventional electromechanical coupling. Under an external electric field, these superelastic membranes undergo controllable and reversible "sushi-rolling-like" 180° folding-unfolding cycles. This crease-free folding is mediated by charged ferroelectric domains, leading to a giant > 3.8 and 4.6 µm displacements for a 30-nm thick membrane at room temperature and 60 °C, respectively. Further increasing the electric field above the coercive value changes the fold curvature, hence augmenting the effective piezoresponse. Finally, it is found that the membranes fold with increasing temperature followed by complete immobility of the membrane above the Curie temperature, allowing us to model the ferroelectric-domain origin of the effect.The electromechanical power conversion of piezoelectrics is the basis for a broad range of sensing, actuating, and communication technologies, including ultrasound imaging and cellular phones. 1-3 Recent interest in electromechanical energy harvesting 4,5 as well as in flexible electronics for wearable devices, 6,7 nano motors, 8 and medical applications 9-11 raises a need for flexible piezoelectric materials and devices. Modern applications of piezoelectrics hinge on thin films, 12-14 however, the substrate in such geometries is typically rigid, preventing the development of flexible devices. Flexible piezoelectric devices are therefore typically based on either nanowires 4 or on thin-film systems, but with substrates that have been designed especially for such applications. 15,16 Most piezoelectric applications rely on lead-based materials, which exhibit strong piezoelectric coefficients. Nevertheless, the toxicity of these materials is undesirable for environmental considerations, while it also disqualifies them for medical or wearable applications. Likewise, traditional thin-film geometries limit the electromechanical excitation modes. That is, usually, uniaxial electric field results in either parallel or perpendicular uniaxial or biaxial mechanical deformation (or vice versa).Nevertheless, the interest in flexible-electronic technologies raises a need for advanced electromechanical excitation modes, e.g., for motorized devices, including microscale aerial vehicles. 17 Substrate removal for piezoelectric films or membranes augments their functional properties, 18-21 mainly thanks to mechanically-induced ferroic-domain reorganization. 22 However, the preparation of completely stand-alone substrate-free films has remained a challenge. Lu et al. 23 demonstrated lately a general method to prepare oxide materials in the form of membranes, i.e., continuous free-standing thin films with no substrate. More recently, Dong et al. 24 used this method to process BaTiO3 membranes, which is a well-known lead-free piezoelectric and ferroelectric material. This work show...

Beyond Substrates: Strain Engineering of Ferroelectric Membranes

“…The La 0.7 Sr 0.3 MnO 3‐ δ layer serves as an epitaxial, sacrificial‐release layer that maintains the quality of the heterostructure, but allows for complete release of the symmetric trilayers upon immersion in an acidic solution (Experimental Section and Figure S1, Supporting Information). This etching process is highly selective to the sacrificial layer—as proven in previous works [ 17,36,51,52 ] —and millimeter‐size membranes with few or no visible cracks could be repeatedly produced (Figure S2–S3, Supporting Information). Following growth, these membranes were then transferred to either rigid silicon or flexible poly(ethylene terephthalate) (PET) substrates ( Figure a, Experimental Section, and Supporting Information).…”

“…[31][32][33][34] While strain is typically introduced by lattice mismatch with a substrate in epitaxial films, released films relax their lattice towards their bulk crystal structure; therefore, different approaches to manipulate properties are required. Mechanical and electric-field manipulation of micrometer-sized freestanding flakes in electron-microscopy experiments [35,36] and straining experiments on polymersupported ultrathin perovskite membranes (restricted to films <10 nm in thickness) [37,38] have demonstrated their exceptional flexibility. Whereas transfer to polymers or electroactive substrates has been exploited to tune magnetic properties, [38][39][40] test the resilience of ferroelectric properties, [41][42][43] or induce ferroelectricity in non-polar materials, [44] deterministic strain control of properties has not been demonstrated on single-crystal ferroelectric membranes.…”

Direct processing of PbZr0.53Ti0.47O3 films on glass and polymeric substrates

“…Such delicate methods, however, significantly complicate the fabrication and integration processes due to the additional transfer step. An alternative complex oxide layer transfer technique releases the ferroelectric single crystal layer by etching the sacrificial layer beneath and uses a transfer stamp to transfer single crystal ferroelectric material layer onto targeted substrates [10,11]. However, the selection of sacrificial material is challenging due to a required low lattice mismatch with the ferroelectric material, and inertness of the ferroelectric material to the etchant used for the sacrificial material.…”

Super‐Flexible Freestanding BiMnO3 Membranes with Stable Ferroelectricity and Ferromagnetism

“…Recent works show that the ferroelectric domain plays a significant role in the super‐elasticity of freestanding membranes. [ 26 , 39 ] Likewise, the super‐flexibility of our BMO membranes most likely also stems from polarization domains to accommodate the flexure excitation for releasing strain.…”