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The development of high‐performance (K,Na)NbO3 (KNN)‐based lead‐free piezoceramics for next‐generation electronic devices is crucial for achieving environmentally sustainable society. However, despite recent improvements in piezoelectric coefficients, correlating their properties to underlying multiscale structures remains a key issue for high‐performance KNN‐based ceramics with complex phase boundaries. Here, this study proposes a medium‐entropy strategy to design "local polymorphic distortion" in conjunction with the construction of uniformly oversize grains in the newly developed KNN solid‐solution, resulting in a novel large‐size hierarchical domain architecture (≈0.7 µm wide). Such a structure not only facilitates polarization rotation but also ensures a large residual polarization, which significantly improves the piezoelectricity (≈3.2 times) and obtains a giant energy harvesting performance (Wout = 2.44 mW, PD = 35.32 µW mm−3, outperforming most lead‐free piezoceramics). This study confirms the coexistence of multiphase through the atomic‐resolution polarization features and analyzes the domain/phase transition mechanisms using in situ electric field structural characterizations, revealing that the electric field induces highly effective multiscale polarization configuration transitions based on T–O–R sequential phase transitions. This study demonstrates a new strategy for designing high‐performance piezoceramics and facilitates the development of lead‐free piezoceramic materials in energy harvesting applications. [ABSTRACT FROM AUTHOR]

Dense (K, Na)NbO3 ceramics are successfully fabricated via the cold sintering process at 350°C under a uniaxial pressure of 400 MPa for 4 h. Equimolar KOH and NaOH solutions were utilized as a transient alkaline flux. The microstructure and dielectric properties were studied in detail. Scanning electron microscope and the relative densities reveal dense structures of the ceramics. After post‐annealing at 800°C for 1 h, the ceramics show good electrical performance. The relative dielectric permittivity is 829 (at 10 kHz) at room temperature, and the piezoelectric constant (d33) reaches up to 148 pC/N. The cold sintering technique with equimolar KOH and NaOH solutions as a transient alkaline flux endow KNN ceramics with excellent dielectric and piezoelectric properties, showing a potential way to fabricating other KNN‐based ceramics at low temperature. [ABSTRACT FROM AUTHOR]

Eco-friendly NaNbO 3 (NN)-based relaxor ferroelectric ceramics with high dielectric constants cannot meet the high piezoelectric activity quality factors (FOMs: d 33 × g 33) requirements of electromechanically coupled devices. To solve this issue, we successfully improved the piezoelectricity of NN-based relaxor piezoceramics while reducing the dielectric constant based on microstructural tuning by virtue of the chemical design and texturing engineering. Mainly affected by the highly <001> c orientation and relaxor MPB, the obtained novel 88.5NaNbO 3 –10Ba(Ti 0.7 Sn 0.3)O 3 –1.5NaSbO 3 texture ceramics enjoys an ultrahigh piezoelectric coefficient (d 33 = 423 pC/N), reaching a record high in NaNbO 3 -based lead-free ceramics. Meanwhile, a large FOMs value (d 33 × g 33 = 13.3·10−12 m2/N) is successfully realized due to the suppression of the dielectric constant. More importantly, the stable phase/domain evolution also encourages excellent temperature stability for piezoelectricity and FOMs. Especially for the piezoelectricity, when the annealing temperature is < 140 °C, the d 33 of the 1.5T ceramics can be stabilized ∼ 400 pC/N. Such excellent electrical temperature stability shows more competition in the reported NN-based piezoceramics. This work not only provides a design paradigm for high-performance piezoelectric materials, but also facilitates their development in electromechanical coupling devices. [Display omitted] [ABSTRACT FROM AUTHOR]

A complex-ion doping strategy fabricates lead-free BCZT ceramic. The excellent properties (d 33 ∼ 577 pC/N, K t ∼ 52%, T C ∼ 110 °C, d ∗ 33 ∼ 620 pm/V, ε r ∼ 1820, tanδ ∼ 0.02) were obtained in BCZT ceramic. The in-situ Raman spectroscopy and PFM were conducted to reveal the mechanisms for the superior properties achieved. BCZT ceramics were manufactured for cement-based piezoelectric composites, including 0–3, 2-2 and 1–3 types. 0–3 type (50% BCZT) showed the properties (d 33 ∼ 46 pC/N, ε r ∼ 310 and K t ∼ 18.1%). 2-2 and 1–3 types exhibited good piezoelectric properties (d 33 ∼ 285 pC/N, ε r ∼ 720 and K t ∼ 33.4% for 2-2 type; d 33 ∼ 238 pC/N, ε r ∼ 485 and K t ∼ 29.5% for 1–3 type). Temperature-dependent electrical properties of BCZT-cement composites were systematically explored. Additionally, BCZT ceramic was designed and fabricated for PCD vibration energy harvesting. The output voltage (∼4.9 V) and output power (∼2.4 mW) were obtained. This work underpins the significance of lead-free BCZT ceramic and cement-based piezoelectric composites, and promotes their applications in smart structures. The eco-friendly BCZT ceramic with excellent properties can serve as a promising alternative to lead-based materials for application of building and concrete structure fields. [Display omitted] • A complex-ion doping strategy fabricates a superior lead-free piezoelectric ceramic (Ba 0.85 Ca 0.15)(Ti 0.9 Zr 0.1)O 3 (BCZT). • The 0–3, 2-2 and 1–3 types BCZT/cement composites were manufactured. • The piezoelectricity in response to temperature variation was explored by in-situ measurements. • Temperature-dependent dielectric constants and dielectric losses of BCZT-cement composites were systematically explored. • Output power (∼2.4 mW) was realized by BCZT vibration energy harvesting. [ABSTRACT FROM AUTHOR]

Two problems plague the field of electro-strain research: low electro-strain performance and high hysteresis. These two key factors are often difficult to optimise simultaneously. Therefore, a novel texture engineering strategy is proposed to obtain ultra-high strain while effectively reducing strain hysteresis. Synergistically optimized textured ceramics with a high degree of orientation in <001> direction were achieved by improving the preparation process based on the conventional TGG method through a heterogeneous template distinct from the ceramic substrate. Finally, the normalized strain of 951 pm/V at 40 kV/cm is obtained in the BNT-based lead-free system, and the strain hysteresis is only 43 %. At the same time, a series of in-situ electric field structural characterization reveal the source of high strain and low hysteresis of the textured ceramics: heterogeneous templates caused high polarization and formed a large number of PNRs. This result is of great significance for the study of electro-strain in lead-free piezoelectric materials and the development of actuators. [ABSTRACT FROM AUTHOR]

Transparent ferroelectrics with high piezoelectricity are highly desirable for acousto-optic-electrical multifunctional coupling devices. However, it is challenging to simultaneously achieve high piezoelectricity and perfect transparency in lead-free piezoelectric ceramics because of the contradiction between the inherent characteristics of traditional high piezoelectricity and the transparency. Here, we demonstrate an efficient method to tailoring the microstructure in originally poor piezoelectricity fine-grain KNN-BNN ceramics to simultaneously exhibit excellent transparency, an superior piezoelectric coefficient (∼185 pC/N, highest in KNN-based transparent ceramics), an excellent EO coefficient (∼84 pm/V), and high T c (∼350 °C). Combining the multiple in-situ characterizations and DFT simulations, we found that both the piezoelectricity and EO effect of fine-grain KNN transparent ceramics can be greatly improved without greatly reducing the transparency via tailoring the structure of phase and domains to enhance local inhomogeneity, enabling prominent acousto-optic-electrical multifunctional coupling in vivid potential applications, such as self-energy-harvesting touch screens, invisible robotic devices and electro-optic (EO) devices. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] Excellent breakdown electric field and ultrahigh power density can be obtained in this work via multi-scale domain and microstructure engineering. • Multi-scale domain and microstructure engineering of BCZT-based ceramics. • Ultra-fast t0.9 (55 ns) and giant PD (369.9 MW/cm3) were realized. • High Wrec (5.32 J/cm3) and η (∼90%) obtained at 620 kV/cm. • Energy storage properties of BCZT-NBN-HP ceramic exhibit superior stability. Fulfilling the stringent demand of the miniature and eco-friendly pulsed power devices, development of high-energy-storage lead-free dielectric energy storage is critical. To achieve this goal, the mature strategy is to induce the formation of relaxor polar nano regions (PNRs) by means of constructing multiple solid solutions and element doping, which will inevitably lead to a significantly weakened polarization. How to better achieve the domain regulation is a challenge. Here, we reconsidered binary composite-induced domain evolution and designed a novel BT-based binary system with Na 0.7 Bi 0.1 NbO 3 (NBN) modification. By adjusting the NBN content to retain the long-range ferroelectric domains and applying the hot-pressing (HP) method to modulate grain size, the coupling of multi-scale domain morphology and voltage allocation can be achieved, simultaneously contributing to the high polarization, the enhanced breakdown strength and the optimized polarization response. Accordingly, a 130% enhancement to 5.32 J/cm3 in energy storage density, a high energy storage efficiency of ∼ 90%, an ultrafast discharge period of ∼ 55 ns, and a giant power density of ∼ 369.9 MW/cm3 were realized in our HP ceramics, superior to the existing dielectric ceramics. Moreover, the energy storage properties also exhibited superior frequency and thermal stability. The proposed synergistic optimization strategy of the domain morphology regulation and the microstructure adjustment is valuable for further energy storage design, and the enhanced energy storage properties promote the applications for lead-free dielectrics in energy storage devices. [ABSTRACT FROM AUTHOR]

The lead-free Er 3+ -doped (K 0.48 Na 0.48 Li 0.04 )(Nb 0.96 Bi 0.04 )O 3 (KNLNB-Er-x) ceramics were fabricated by conventional pressureless sintering. They possess a tetragonal perovskite phase with dense microstructure. High transmittances of the ceramics are obtained both in the visible and infrared regions. The optical band gap energies of them are 3.07–3.11 eV, close to other KNN-based materials. The relaxor-like characteristics, good dielectric, ferroelectric and piezoelectric properties of the ceramics have been obtained. The up-conversion photoluminescence spectra have been studied and obvious color-tunable emissions have been observed by modulating temperature. The fluorescence intensity ratio (FIR) value based on green emissions at 533 and 555 nm in the temperature ranging from 300 to 750 K have been investigated, giving the maximum sensitivity of ~ 0.0038 K −1 . Furthermore, the FIR technique opens up a method to detect the Curie temperature of the ceramics. Owing to both optical and electrical properties, the KNLNB-Er-x transparent ceramics could be a promising candidate in the application of color-tunable solid-state lightings, optical temperature sensors, and electrical-optical coupling devices. [ABSTRACT FROM AUTHOR]

• The local defect structure design is proposed to achieve high energy storage density in NN-based AFE ceramics. • The pinning effect of defect dipoles and the increased local structural disorder stabilize the AFE phase. • High energy storage characteristics (W rec ∼ 9.7 J/cm3, η ∼ 88.75 %) with near-zero P r. • Excellent charge–discharge performance (P D ∼413.2 MW/cm3, W D ∼4.47 J/cm3). Antiferroelectrics (AFEs) are ideal candidates in dielectric, electromechanical, and electrothermal applications. NaNbO 3 (NN), as a lead-free antiferroelectric (AFE) material under extensive investigation, exhibits ferroelectric (FE)-like polarization–electric field (P-E) hysteresis loops, characterized by high remnant polarization and large hysteresis. Herein, the local defect structure design is proposed to achieve high energy storage (ES) density in NN-based AFE ceramics. The pinning effect of defect dipoles and the enhancement of local structural disorder stabilize the AFE phase and reduce hysteresis losses. Consequently, an excellent ES performance of large recoverable energy density (W rec) of 9.70 J/cm3 and high efficiency (η) of 88.75 % is concurrently obtained in NN-based relaxor AFE ceramics, with outstanding charge–discharge performance (P D ∼413.2 MW/cm3, W D ∼4.47 J/cm3), which are significantly improved compared to other reported values in lead-free ES ceramics. This indicates that NN-based ceramics are candidates for advanced ES capacitors and provides a feasible modulation approach for the development of new lead-free high-performance dielectric materials. [ABSTRACT FROM AUTHOR]

• The BNT-BT- x BFOMT polycrystalline thin films were successfully prepared on Pt (111)/Ti/SiO 2 /Si (100) substrates by the sol-gel method. • The coexistence of long-range ordered and short-range disordered nanodomains is realized in the multi-phase BNT-0.06BT-0.01BFOMT thin film. • This kind of coexisting domain structure can reduce the potential barrier and the hysteresis, and improve the piezoelectric properties significantly. • The piezoelectric properties of the BNT-BT thin films are enhanced nearly 2.3 times. Although the multi-phase coexistence makes Bi 0.5 Na 0.5 TiO 3 -based piezoelectric thin films possess stronger piezoelectric properties and more spacious application prospects in electronic devices, the domain reversal mechanism of Bi 0.5 Na 0.5 TiO 3 -based thin films cannot be accurately understood due to the size effect. In this study, the relationship between domain structure and piezoelectric properties of the (0.94-x)Bi 0.5 Na 0.5 TiO 3 -0.06BaTiO 3 -xBi(Fe 0.95 Mn 0.03 Ti 0.02)O 3 thin films are studied by using visualization technology PFM, structure and electrical properties characterizations. The results show that the addition of Bi(Fe 0.95 Mn 0.03 Ti 0.02)O 3 creates a long-range ordered/short-range disordered nanodomain coexisting structure. This kind of coexisting domain structure can realize the long-range reversal driven by disordered nanodomains under the external electric field, reduce the potential barrier and the hysteresis, and significantly enhance the piezoelectric properties of the thin films. Under the same conditions, the piezoelectric properties of the 0.94Bi 0.5 Na 0.5 TiO 3 -0.06BaTiO 3 thin films are enhanced nearly 2.3 times. This provides a reference for exploring the physical mechanism of high performance lead-free piezoelectric thin films. [ABSTRACT FROM AUTHOR]

Current interests in electrocaloric (EC) and electromechanical (EM) effects have been stimulated by the discovery that self-actuating electrocaloric materials designed by using the electrostrain and entropy change (Δ S) characteristics of relaxor ferroelectrics are particularly appealing for applications in intelligent refrigeration devices. Herein, the lead-free Bi 0.5 Na 0.5 TiO 3 -based (BNT) ceramics designed by A-site defect engineering (ADE) can realize the collaborative EM and EC responses, e.g. obtaining electrostrain ∼ 0.47%, electrostrictive coefficient ∼ 0.031 m4 C−2 and EC temperature change ∼ -0.512 K at room temperature. The temperature-dependent polarization electric current behaviors and local structures of ADE system show slowly-evolving nonergodic-ergodic transitions, corresponding to the EC and EM behaviors with a wide operating temperature range (i.e. electrostrain > 0.3% and electrostrictive coefficient > 0.030 m4 C−2 within 105 °C, EC temperature change > 0.400 K within 50–125 °C). Landau theory shows that ADE method can reduce the barrier of high temperature disturbance. Furthermore, the uniform distributions of sodium and oxygen vacancies are conducive to the electric field response and orientation of the local dipoles. Most importantly, this work will further facilitate the development of self-actuating refrigeration materials/devices and provide an alternative concept to combine EM and EC effects by introducing A-site defects. [Display omitted] [ABSTRACT FROM AUTHOR]

• Inducing relaxor evolution by adjusting intrinsic A-site Na+/K+ ratio. • Achieving large combined electromechanical and electrocaloric responses. • Realizing a larger electrocaloric endothermic peak at a low electric field. • Obtaining high electrocaloric strength and large electrostrictive coefficient. • Broadening the operating-temperature span. Self-actuating cooling materials based on synergistic electromechanical (EM) and electrocaloric (EC) responses are expected to lead next-generation of intelligent cooling devices. However, most current materials with the two responses present poor performance, narrow operation-temperature span and high driving electric field, and even contain toxic lead. Here, environmentally benign lead-free Bi 0.5 Na 0.5 TiO 3 -based (BNT) system was designed to achieve large combined response of two effects in a large temperature span by adjusting intrinsic A-site Na+/K+ ratio to induce relaxor evolution. Simultaneously, high EC strength and large electrostrictive coefficient over a wide temperature range were obtained to resolve these challenges. The local-structural evolution is studied in detail to provide a theoretical basis for future application of this intelligent material. A novel asymmetric EC response presenting a larger endothermic peak was realized at a low electric field (<3 kV mm−1), which can provide a guideline for the development of low-driving-field EC materials to a certain extent. The phase-field simulation was performed to predict this unique behavior by describing the corresponding dipole coupling states under various electric fields. [ABSTRACT FROM AUTHOR]

[001]-oriented (1- x)BiFeO 3 - x BaTiO 3 (x = 0.2, 0.3 0.4; BF-BT) ceramics were prepared by templated grain growth (TGG) method. BaTiO 3 (BT) templates existed stably in less BF ceramics, resulting in the highest orientation degree (f) of 72 % for 0.6BiFeO 3 -0.4BaTiO 3. The BaTiO 3 templates significantly improved the remanent polarization of samples, indicating that more oriented domain left after removing the electric field. Furthermore, the domain of textured 0.7BiFeO 3 -0.3BaTiO 3 (0.7BFBT-T) switched more quickly and easily than the random one. Therefore, the poling electric field (E p) of 0.7BFBT-T (2.5 kV/mm) was much lower than reported BF-based samples (4-5 kV/mm). Rapidly poling under low DC field of 0.7BFBT-T was observed, the d 33 value of 0.7BFBT-T reached 96 % when poled at 2.5 kV/mm in 1 min. BaTiO 3 modified [001] oriented BiFeO 3 -BaTiO 3 ceramics were prepared. BaTiO 3 templates existed stably in less BF ceramics, resulting in the highest orientation value of 72 %. The d 33 value that of 0.7BFBT-T was 1.80 times that of random one when poled at 1.0 kV/mm for 20 min. A very rapid piezoelectric response of textured 0.7BiFeO 3 -0.3BaTiO 3 was observed, the d 33 value of 0.7BFBT-T reached 96 % when poled at 2.5 kV/mm for 1 min. The rapid poling process was attributed to the enhanced remanent polarization and easily switching of domain. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • • Sandwich structured ceramics were prepared successfully by tape casting technique. • • The polarization and electric breakdown strength can be optimized synchronously. • • Ultrahigh energy storage capability (W rec ~ 6 J cm−3, η ~ 95%) can be achieved. • • Energy storage properties exhibited outstanding thermal, frequency and cycle stability. With the rapid development of electronic information technology and the rising environmental concerns as well as the tendency of electronic devices towards miniaturization and integration, enhancing the energy storage properties of lead-free ceramic capacitors is one of the imperative issues. Although a large number of efforts have been contributed to optimize the energy storage properties of lead-free ceramics, the conflict between the polarization and electric breakdown strength seriously impedes the improvement of energy storage density significantly. Herein, inspired by the layered composites of sandwich, the sandwich structured lead-free ceramics based on Bi 0.5 Na 0.5 TiO 3 were designed and fabricated to overcome the above challenge effectively. The theoretical simulations and experiment results demonstrate that the polarization and electric breakdown strength can be optimized synchronously via the sandwich structured design. An ultrahigh recoverable energy storage density of ~ 6 J cm−3 and a nearly ideal energy conversion efficiency of ~ 95% can be obtained for the prepared sandwich structured lead-free ceramics. Meanwhile, the maximum applied electric field can be enhanced to more than 500 kV cm−1. The energy storage capabilities also exhibit outstanding stability over a broad temperature range, frequency range and cycle numbers. These results reveal that the Bi 0.5 Na 0.5 TiO 3 -based lead-free ceramics of this study have a great potential for high energy storage capacitors applications. [ABSTRACT FROM AUTHOR]