![]() ![]() 14 combined field-induced phase transitions and charged point defects to improve electrostrain. ![]() Constructing reversible electric field-induced phase transitions through ionic doping can increase the crystal symmetry 7, 12, 13. The stability of defects becomes the key point in influencing the strain stability, especially under the electric and thermal fields, which could irreversibly control oxygen vacancy concentration 11. The introduction of defects can provide a restoring force for the reversible switching in non-180° domains and exhibit a huge recoverable strain of 0.75% 10, but the formation of defects depends on the aging process. However, an MPB does not normally show a large reverse switching of the ferroelectric domains or an improvement of the electrostrain. ![]() Generally, constructing a morphotropic phase boundary (MPB) can produce coupling of different polarization directions in different phases and thus significantly improve the small-signal piezoelectric response d 33. Extrinsic contributions come from the switching of non-180° domains and volume changes produced by the non-ferroelectric to ferroelectric phase change 9. Intrinsic contributions originate from piezoelectric and electrostrictive effects. The contribution of electrostrain is divided into two parts: intrinsic contributions and extrinsic contributions. In principle, a large electrostrain can be achieved through multi-scale engineering of the composition-structure-property relationship. For example, the maximum electrostrain at high temperature is below 0.6% 7. Furthermore, in the last few decades there have been few advances in achieving large electrostrain at high temperatures (over 200 ☌). Therefore, achieving larger electrostrain in piezoelectric materials, especially in lead-free materials, is a crucial requirement for the actuation application. Even though the ban on lead in commercial electronic products is gradually being implemented, lead-based piezoelectric materials are still in an irreplaceable position in some highly sophisticated technologies and aerospace. In addition, the lead element is restricted by the Restriction of Hazardous Substances (RoHS) Directive and the Waste Electrical and Electronic Equipment (WEEE) Directive due to its toxicity and damage to the environment. For instance, the maximum electrostrain reported in lead-free polycrystalline piezoceramic is below 0.7% 7, while the maximum electrostrain reported in lead-based polycrystalline piezoceramic is 1.3% 8. Unfortunately, the electrostrain of polycrystalline piezoceramics is much lower than that of single crystals. In contrast to single crystal, developing non-textured polycrystalline piezoelectric consumes lower cost, shorter time, and less energy, providing a practical solution for large-scale applications. However, the growth of high-quality single crystals has many disadvantages such as high cost, complex and delicate control of experimental parameters, and harsh environments, which preclude practical applications of them 6. The benchmark electrostrain of 1.7% was reported in single crystals of Pb(Zn 1/3Nb 2/3)O 3–PbTiO 3 (PZN-PT) 5. shape memory alloys 1, electrorheological materials 2, 3, and magnetostrictive materials 4, piezoelectric actuators have the advantage of fast response, good frequency characteristics, and resistance to electromagnetic interference. Compared with other classes of materials that strain under the action of external physical stimulation, e.g. Piezoelectrics undergo strain in response to stimulation by an electric field and function in a responsive and controlled mode. Piezoelectric materials are universal and important materials for a variety of applications, such as actuators and sensors. We demonstrate practical solutions for achieving high electrostrain in low-cost environmentally piezoelectric for various applications. We achieve an ultrahigh electrostrain of 2.3% at high temperature (220 ☌) in lead-free polycrystalline ceramics, higher than all state-of-the-art piezoelectric materials, including lead-free and lead-based ceramics and single crystals. In this work, we report one strategy to enhance the electrostrain via designing “heterostrain” through atomic-scale defect engineering and mesoscale domain engineering. Developing high-strain piezoelectric materials has been a long-term challenge, particularly challenging for the design of high-strain polycrystalline piezoelectrics containing no toxic lead element. Although they were discovered over 100 years ago, scientists are still searching for alternative lead-free piezoelectrics to reduce their environmental impact. Piezoelectric materials provide high strain and large driving forces in actuators and can transform electrical energy into mechanical energy. ![]()
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