With growing concern over world environmental problems and increasing legislative restriction on using lead and lead-containing materials, a feasible replacement for lead-based piezoceramics is desperately needed. Herein, we report a large piezoelectric strain (d*) of 470 pm/V and a high Curie temperature (T) of 243 °C in (NaK)NbO-(BiLi)TiO-BaZrO lead-free ceramics by doping MnO. Moreover, excellent temperature stability is also observed from room temperature to 170 °C (430 pm/V at 100 °C and 370 pm/V at 170 °C). Thermally stimulated depolarization currents (TSDC) analysis reveals the reduced defects and improved ferroelectricity in MnO-doped piezoceramics from a macroscopic view. Local poling experiments and local switching spectroscopy piezoresponse force microscopy (SS-PFM) demonstrates the enhanced ferroelectricity and domain mobility from a microscopic view. Distinct grain growth and improvement in phase angle may also account for the enhancement of piezoelectric properties.

Because of the environmental concerns of eliminating lead from piezoelectric products, bismuth‐based perovskite is becoming one of the most potential candidates. However, its relatively low thermal depolarization temperature (Td) is still an imperative obstacle hindering implementation of this material for practical application. Here, an enhanced temperature stability of 0.94(Bi0.5Na0.5)TiO3‐0.06BaTiO3 (BNTBT6) piezoceramics is reported, which can be obtained by the effective quenching process. Quenching process enhances the depolarization temperature to 136 °C, which is 40 °C higher than that of normal sintered samples. By using X‐ray photoelectron spectroscopy and electron paramagnetic resonance methods, it is revealed that oxygen vacancy may exist in the quenched samples and consequently pins the domain walls, resulting in significant enhancement of depolarization temperature. Temperature‐dependent dielectric, piezoelectric, and ferroelectric behaviors are measured as criteria to evidence the enhanced temperature stability.

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Defect engineering is a well‐established approach to customize the functionalities of perovskite oxides. In demanding high‐power applications of piezoelectric materials, acceptor doping serves as the state‐of‐the‐art hardening approach, but inevitably deteriorates the electromechanical properties. Here, a new hardening effect associated with isolated oxygen vacancies for achieving well‐balanced performances is proposed. Guided by theoretical design, a well‐balanced performance of mechanical quality factor (Qm) and piezoelectric coefficient (d33) is achieved in lead‐free potassium sodium niobate ceramics, where Qm increases by over 60% while d33 remains almost unchanged. By atomic‐scale Z‐contrast imaging, hysteresis measurement, and quantitative piezoresponse force microscopy analysis, it is revealed that the improved Qm results from the inhibition of both extrinsic and intrinsic losses while the unchanged d33 is associated with the polarization contributions being retained. More encouragingly, the hardening effect shows exceptional stability with increasing vibration velocity, offering potential in material design for practical high‐power applications such as pharmaceutical extraction and ultrasonic osteotomes.

Lead zirconate titanate (PZT)‐based piezoelectric ceramics are important functional materials for various electromechanical applications, including sensors, actuators, and transducers. High piezoelectric coefficient and mechanical quality factor are essential for the resonant piezoelectric application. However, since these properties are often inversely proportional, simultaneously high performances are hard to achieve, consequently, a wide range of applications are strongly restricted. In the present study, exceptionally well‐balanced performances are achieved in PZT‐based ceramics via innovative defect engineering, which involves multi‐scale coordination among defect dipole, domain‐wall density, and grain boundary. These materials are superior to many state‐of‐the‐art commercial counterparts, which can potentially satisfy high‐end requirements for advanced electromechanical applications, such as energy harvesting, structural health monitoring, robotic sensors, and actuator.

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