Low electric field-induced ultrahigh strain in lead-free piezoelectric via synergistic approach of phase and defect engineering

Achieving ultrahigh-strain performance under a low electric field with good thermal stability in polycrystalline ceramics is a major challenge for high-temperature piezoelectric actuators. The design of material composition is strongly correlated with phase structure, domain configuration, and functional properties. In this work, we employed a synergistic approach of phase, defect, and domain engineering to enhance piezoelectric strain performance in the (K, Na)NbO 3 ceramics. A judicious heterovalent chemical modification introduces random local fields that generate structural heterogeneity and also converges the polymorphic phase boundary to near room temperature. Consequently, both piezoelectric performance and thermal stability are simultaneously improved. An ultrahigh piezoelectric voltage coefficient ( d 33 *) exceeding 3700 pm/V is achieved under the low driving electric field of 20-25 kV/cm, along with high Curie temperature ( T C ∼300 °C). Phase field simulation strongly supports the proposed theory of composition design and is consistent with experimental results. The high electrostrain obtained in these lead-free polycrystalline ceramics surpasses that of state-of-the-art piezoceramics. Therefore, the applied strategy in this work provides a new paradigm for boosting piezoelectric strain performance and thermal stability in the development of piezoelectric actuator devices.