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...

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