Piezoelectric actuators are indispensable over a wide range of industries for their fast response and precise displacement. Most commercial piezoelectric actuators contain lead, posing environmental challenges. We show that a giant strain (1.05%) and a large-signal piezoelectric strain coefficient (2100 picometer/volt) are achieved in strontium (Sr)–doped (K,Na)NbO ₃ lead-free piezoceramics, being synthesized by the conventional solid-state reaction method without any post treatment. The underlying mechanism responsible for the ultrahigh electrostrain is the interaction between defect dipoles and domain switching. The fatigue resistance, thermal stability, and strain value (0.25%) at 20 kilovolt/centimeter are comparable with or better than those of commercial Pb(Zr,Ti)O ₃ -based ceramics, showing great potential for practical applications. This material may provide a lead-free alternative with a simple composition for piezoelectric actuators and a paradigm for the design of high-performance piezoelectrics.

In the past century, ferroelectrics are well known in electroceramics and microelectronics for their unique ferroelectric, piezoelectric, pyroelectric, and photovoltaic effects. Nowadays, the advances in understanding and tuning of these properties have greatly promoted a broader application potential especially in energy and environmental fields, by harvesting solar, mechanical, and heat energies. For example, high piezoelectricity and high pyroelectricity can be designed by defect or microstructure engineering for piezo‐ and pyro‐catalyst, respectively. Moreover, highly piezoelectric and broadband (UV–Vis–NIR) light‐responsive ferroelectrics can be designed via defect engineering, giving rise to a new concept of photoferroelectrics for efficient photocatalysis, piezocatalysis, pyrocatalysis, and related cocatalysis. This article first summarizes the recent developments in ferroelectrics in terms of piezoelectricity, pyroelectricity, and photovoltaic effects based on defect and microstructure engineering. Then, the potential applications in energy generation (i.e., photovoltaic effect, H₂ generation, and self‐powered multisource energy harvesting and signal sensing) and environmental protection (i.e., photo‐piezo‐pyro‐ cocatalytic dye degradation and CO₂ reduction) are reviewed. Finally, the outlook and challenges are discussed. This article not only covers an overview of the state‐of‐art advances of ferroelectrics, but also prospects their applications in coping with energy crisis and environmental pollution.

(Nay,Biz)Ti1-xO3(1-x)-xBaTiO3 ceramics with an excess in Bi3+ and/or a deficiency in Na+ were prepared and investigated. It is found that an antiferroelectric phase can be induced through a modulation of the mole ratio of Na+ and Bi3+. A phase boundary between ferroelectric and antiferroelectric phases can be observed at ambient temperature. A modulated phase, which is the origin of relaxor antiferroelectric behavior, should be attributed to a compositional modulation. The antiferroelectric phase can be induced to the ferroelectric phase by an applied electric field. The stability of the induced ferroelectric phase strongly depends on the mole ratio of Na+ and Bi3+. A recoverable giant strain of 0.48% comparable to PbZrO3-based antiferroelectrics as well as electrostrictive coefficients (0.026 C4$\hskip0.3em${}m-2) much higher than lead-based relaxor ferroelectrics with low-temperature dependence was achieved in (Nay,Biz)Ti1-xO3(1-x)-xBaTiO3 antiferroelectrics. Our results show there is a high possibility that the novel lead-free antiferroelectrics will replace the PbZrO3-based ones.

Self-doped, [010] oriented BiVO₄nanorods with plentiful oxygen vacancies on the surface exhibit strong adsorbability and highly efficient photocatalytic activity.