![]() Delicate control of complex stoichiometry, with the aid of external dopants, is often crucial for achieving the desired multiphase coexistence and local heterogeneity. Nanoscale structural and chemical heterogeneity at MPBs plays major roles in achieving a large piezoelectric response by flattening the thermodynamic energy surface 4, 5. This approach involves the engineering of chemical composition to have competing polar phases with similar energies but different structures, leading to a large strain with polarization rotation under external electric field 1, 2, 3. A common approach is to control oxide perovskite ferroelectric compositions in relation to morphotropic phase boundaries (MPBs), where a large electromechanical coupling effect can be realized 2, 3, 4. This is especially the case for lead-free oxide systems with environmental and regulatory drivers 1. There is an extensive ongoing quest for piezoelectrics with a large electromechanical response. Our findings demonstrate an important mechanism for realizing the unprecedentedly giant electromechanical coupling and can be extended to many other material functions by engineering lattice faults in non-stoichiometric compositions. The large oxygen octahedral distortions and the coupling between the structural distortion and polarization orientation mediated by charge redistribution at the planar faults enable the giant electric-field-induced strain. A giant piezoelectric coefficient of ∼1900 picometer per volt is demonstrated at 1 kHz, which is almost double the highest ever reported effective piezoelectric response in any existing thin films. This is in non-stoichiometric potassium sodium niobate epitaxial thin films with a high density of self-assembled planar faults. Here, we elucidate its origin in terms of atomic structure and demonstrate a different system with a greatly enhanced response. Recently it was shown that giant piezoelectricity can be obtained in films with nanopillar structures. Enhanced electromechanical coupling in ferroelectrics is usually obtained at morphotropic phase boundaries requiring stoichiometric control of complex compositions. ![]() A large electromechanical response in ferroelectrics is highly desirable for developing high-performance sensors and actuators. ![]()
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