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Although a large electric-induced strain has been obtained in sodium bismuth titanate (Bi0.5Na0.5TiO3, BNT)-based ceramics using chemical modifications, the effect of initial BNT-based ceramic's polarity on modulating strain properties was rarely reported. Herein, we comparatively studied the effect of tantalum (Ta) doping on two BNT-based ceramics with different ferroelectric polarities, namely, (Bi0.5Na0.5)0.935Ba0.065TiO3–0.7%Bi2FeCrO6 and (Bi0.98Gd0.02)0.5Na0.5TiO3. The former locates at the morphotropic phase boundary (MPB), whereas the latter is close to pristine BNT ceramics. An effective critical point, located at the crossover between ferroelectric and relaxor, is constructed in the former ceramic and significantly enhances strain properties, whereas a useless one is found in the latter ceramic due to the retention of a non-ergodic relaxor and has merely limited ability to promote strain properties. Our results demonstrate that the ferroelectric polarity of the initial BNT-based ceramic matrix also plays an important role in pursuing high strain properties. [ABSTRACT FROM AUTHOR]

Although piezocatalysis has achieved preliminary achievements in environmental remediation and biomedical applications, large‐scale fabrication of piezocatalysts with high degradation efficiency and low cost remains challenging. In this work, a new and easy strategy to solve this challenge is innovatively proposed, that is, ceramic‐powder‐driven boosted polarization intensity, and validated the strategy is by examining potassium sodium niobate ((K, Na)NbO3, KNN) ferroelectric. KNN‐3 piezocatalyst, obtained by grinding as‐sintered ceramics into powder, shows a degradation rate (k) as high as 148 × 10−3 min−1 for rhodamine B (RhB) dye and for 31 × 10−3 min−1 for methyl orange (MO) dye, ≈18 times and 66 times than those of previously reported KNN piezocatalysts. The superior piezocatalytic activity is attributed to enhanced polarization intensity, increased oxygen vacancies, and higher charge carrier concentrations. Besides, the KNN‐3 piezocatalyst shows excellent inhibitory effects on Staphylococcus aureus and Escherichia coli strains. Therefore, the proven ceramic preparation technology enables the new strategy to mass produce high‐performance KNN piezocatalysts that hold promise for applications in dye degradation and biomedicine. [ABSTRACT FROM AUTHOR]

Although past studies have shown a competitive relationship between bismuth ion (Bi3+) and rare earth ions in potassium sodium niobate {(K, Na)NbO3, KNN}‐based ceramics, a comprehensive investigation of this competition has been relatively scarce. Herein, we conducted an in‐depth exploration of this competition by substituting Bi3+ with praseodymium ions (Pr3+) in KNN‐based ceramics possessing high piezoelectric properties. The substitution of Bi3+ with Pr3+ results in a decrease in the extent of multi‐phase coexistence at room temperature, an increase in domain size and grain size, and the enhancement of ferroelectricity. However, it also leads to a deterioration in piezoelectricity. Through a combination of experimental findings and first‐principles calculations, we analyzed the alterations in phase structure, ferroelectric domains, and electrical properties, attributing these changes to the competitive nature of Bi‐O and Pr‐O bonds with their distinct ionic/covalent characteristics. Consequently, this study not only unveils the underlying physical mechanism behind the competition between Bi3+ and Pr3+ ions in KNN‐based piezoceramics but also presents a novel approach to tailor the phase transition temperature, thereby facilitating the overall performance improvement of KNN‐based ceramics. [ABSTRACT FROM AUTHOR]

Although certain efforts were paid to the effect of K/Na ratio on the phase structure and piezoelectric properties of potassium sodium niobate {(K, Na)NbO3, KNN}‐based ceramics, insufficient attention was given to the local structure and ferroelectric domains, hindering the further understanding of physical mechanisms. Herein, we studied the effect of the K/Na ratio on KNN‐based ceramics with multi‐phase coexistence from multiscale structure. High Na+ content leads to local stress heterogeneity and retains large ferroelectric domains, while high K+ content rotates the NbO6 octahedron and results in local polarity heterogeneity and distinct dielectric relaxational behavior, consequently fragmenting ferroelectric domains. The improved piezoelectricity is obtained at the equal K/Na ratio and originates from the balanced local polarity and stress heterogeneities. Therefore, an appropriate K/Na ratio should be fully considered when designing compositions with the purpose of improving performance of KNN‐based ceramics in the future. [ABSTRACT FROM AUTHOR]

To improve the electrical properties and temperature stability of (K,Na)NbO3 (KNN)-based ceramics, 0.964K0.40Na0.60Nb0.96Sb0.04O3-0.03Bi0.5Na0.5ZrO3-0.006BiFeO3-xZnF2 (KNNS-BNZ-BF-xZnF2, 0.005 ≤ x ≤ 0.030) lead-free ceramics were designed. The effect of ZnF2 content on microstructure and electrical behavior was mainly investigated. Through tuning chemical modifications, the enhancement of electrical properties (d33 ∼478 pC/N, kp ∼0.483, ɛr ∼2759, tan δ∼0.035, Pr ∼17.0 μC/cm2, and EC ∼7.02 kV/cm), large Suni (∼0.195% at 40 kV/cm; 0.235% at 75 kV/cm), and d33* (∼555 pm/V at 20 kV/cm; 488 pm/V at 40 kV/cm) can be obtained for x = 0.015. In addition, excellent strain stability (fluctuation is less than 19% at 25-125 °C) is realized in the ceramics, which is also superior compared to other KNN-based materials and some soft lead-based counterparts. We believe that this work can be beneficial to design lead-free piezoelectric materials with excellent temperature stability and high piezoelectricity. [ABSTRACT FROM AUTHOR]

By studying the alone and synergetic effects of Zr4+ and Bi3+ on potassium sodium niobate ((K, Na)NbO 3 , KNN) ceramics, we revealed how Bi 0.5 A 0.5 ZrO 3 (A = K, Na, Ag, and (Na 0.82 K 0.18)) reduces the orthorhombic-tetragonal phase transition temperature (T O–T) of KNN ceramics. Investigations into the alone effects reveal that aliovalent substitutions on K+/Na+ (Nb5+) with Bi3+ (Zr4+) inevitably destroy long-range ordering (LRO) and thus worsen piezo/ferroelectric properties. Despite this, Zr4+ can replace Nb5+ within a high content, remain an orthorhombic (O) phase, and slightly increase T O–T. Although substituting on K+/Na+ with Bi3+ decreases T O–T , it already significantly destroyed LRO before shifting T O–T to room temperature. Then, investigations into the synergetic effects show that Zr4+ acts as a buffer, Bi3+ is an accelerator, and A+ is a stabilizer. The buffer can exist in KNN ceramics within a high content and neutralizes the charges caused by the accelerator that concentrates on decreasing T O–T, and the stabilizer compensates for the stability of the perovskite phase. Their synergetic effects explain why Bi 0.5 A 0.5 ZrO 3 can gradually reduce the T O–T of KNN ceramics without significantly destroying LRO. Therefore, this work helps understand how Bi 0.5 A 0.5 ZrO 3 decreases T O–T and further design the phase boundary for KNN ceramics. Image, graphical abstract [ABSTRACT FROM AUTHOR]

This work reveals the role of Bi3+ in the controlling ability of (Bi 0.5 Ag 0.5)ZrO 3 to the phase structure of potassium sodium niobate based ceramics by introducing Ba2+. The substitution on (Bi 0.5 Ag 0.5)2+ with Ba2+ results in the reduced degree of phase coexistence, accompanying the phase transition from coexisting orthorhombic-tetragonal (O–T) phases to an orthorhombic (O) phase, which is demonstrated by the systematic phase structure analysis and variations of electrical properties. The analysis reveals that the high electronegativity of Bi3+ results in the increased covalent bond character and then increases the stabilization of the T phase, leading to a decrease in orthorhombic-tetragonal phase transition temperature (T O-T). Therefore, this work not only compares the controlling ability of Ba2+ and (Bi 0.5 Ag 0.5)2+ to T O-T but also reveals which and how elements cause the decreased T O-T , promoting the understanding of the effect of additives on the phase structure. [ABSTRACT FROM AUTHOR]

Developing eco-friendly high-performance piezoceramics without lead has become one of the most advanced frontiers in interdisciplinary research. Although potassium sodium-niobate {(K,Na)NbO3, KNN} based ceramics are believed to be one of the most promising lead-free candidates, the relatively inferior piezoelectric properties and strong temperature dependency have hindered their development for more than 50 years since being discovered in the 1950s. It was not until 2014 that our group initially proposed a new phase boundary (NPB) that simultaneously improved the piezoelectric properties and temperature stability of non-textured KNN-based ceramics to the level of partly lead-based ceramics. The NPB has been then proved by some researchers and believed to pave the way for "lead-free at last" proposed by E. Cross (Nature, 2004, 432, 24). However, the understanding of the NPB is still in its infancy, leaving many controversies, including the phase structure and physical mechanisms at the NPB as well as the essential difference when compared with other phase boundaries. In this context, we systematically summarized the origin and development of the NPB, focusing on the construction, structure and intrinsic trait of the NPB, the effects of the NPB on the performance, and the validity and related incipient devices of the NPB. Particularly, we concluded the phase structure and domain structure locating at the NPB, analyzed the physical mechanisms in depth, proposed the possible methods to further improve the performance at the NPB, and demonstrated the validity and scope of the NPB as well as the device application. Finally, we gave out our perspective on the challenges and future research of KNN-based ceramics with NPB. Therefore, we believe that this review could promote the understanding of the NPB and guide the future work of KNN-based ceramics. [ABSTRACT FROM AUTHOR]

We firstly reported the electrocaloric properties in relaxor (1−x−y)NaNbO3–yBaTiO3–xCaZrO3 ceramics, and high electrocaloric effect (∆T ~0.451 K and∣∆T/∆E∣~0.282 Km/MV) can be realized in the ceramics (x = 0.04 and y = 0.10) under low temperature and low electric field. Relaxor behavior of NaNbO3 ceramics can be found by doping both BaTiO3 and CaZrO3. In addition, optimized piezoelectric effects (d33 ~235 pC/N and d33* ~230 pm/V) can be observed in the ceramics (x = 0.04 and y = 0.10) due to the involved morphotropic phase boundary (MPB). Excellent piezoelectric effect (ie, d33~330 pm/V at 41°C, and d33*~332 pm/V at 60°C) can be found because of the characteristics of MPB. Good temperature reliability of piezoelectric effect can be shown because of both MPB and relaxor behavior. We believe that the ceramics with high electrocaloric effect and good piezoelectric effect can be considered as one of the most promising lead‐free materials for piezoelectric devices. Significant MPB and relaxor behavior can be revealed in NaNbO3 ceramics with BaTiO3 and CaZrO3 modified. Sequentially, the giant electrocaloric effect (?T ~ 0.451 K) and high piezoelectric effect (d33 ~ 330 pm/V) as well as good temperature stability were realized in the ceramics benefit by the MPB and relaxor behavior. It can be believed that this result can partly promote the investigation of lead‐free cermics. [ABSTRACT FROM AUTHOR]

As one of the most important lead-free piezoelectric candidates, potassium sodium niobate [(K, Na)NbO 3 , KNN] has gained popularity due to its attractive functional properties, which are much improved by chemical modifications. However, there still remains an insufficient understanding of how these dopants influence the structure and performance of KNN ceramics. Herein, we comparatively studied a series of changes triggered by introducing (Bi 0.5 Na 0.5)ZrO 3 , BaZrO 3 , and PbZrO 3 into the KNN matrix. The analysis highlights their different roles in modulating the orthorhombic-tetragonal phase transition temperature (T O-T) by considering discrepancies in the electronegativity and radius among Bi3+, Ba2+, and Pb2+ ions. The synergistic effects of the large electronegativity and the small radius of the Bi3+ ion are the key to regulating T O-T , which is relatively unaffected by Pb2+ and Ba2+ ions. Based on experimental results and first-principles calculations, a multi-scale model is proposed to summary the general law of how the electronegativity and radius of the A-site ion in AZrO 3 -type dopants synergistically affect the phase structure, ferroelectric domains, and electrical properties of KNN ceramics. Therefore, this work helps understand the role of chemical dopants in the structure and performance of KNN ceramics and promote the future composition design for high performance. [Display omitted] Proving the large off-center displacement of Bi3+ is the root cause to effectively reduce T O-T and enhance d 33 , which is absent in Pb2+ and Ba2+. [ABSTRACT FROM AUTHOR]

Abstract: (0.99‐x)(K0.5Na0.5)(Nb0.965Sb0.035)O3‐0.01SrZrO3‐x(Bi0.5Na0.5)ZrO3 ceramics are chosen as an example to illustrate the effects of phase boundaries on strain. Temperature‐dependent dielectric permittivity and convergent beam electron diffraction patterns confirm the multiphase coexistence of rhombohedral, orthorhombic, and tetragonal phases in the ceramics with x = 0.03–0.04. Intriguingly, the ceramics with x = 0.03 display improved temperature stability in strain, e.g., a high retention (≈95%) of unipolar strain at 180 °C and low variation of 24% at 20–180 °C. A mode is proposed to show how to effectively tailor the strain and consolidate its temperature stability in potassium sodium niobate‐based ceramics. [ABSTRACT FROM AUTHOR]

We report a novel method to prepare translucent and stable Ag@AgCl/g-C 3 N 4 /TiO 2 ceramic films having strong photocatalytic activities and self-cleaning capabilities under light irradiation. Colloidal silica was used as an inorganic binder and P25 TiO 2 was added as a hydrophilicity enhancer without which a smooth coating was not achievable. Ag@AgCl of particle size around 30 nm, was synthesized by in-situ oxidation of nano-silver particles in porous g-C 3 N 4 /TiO 2 films. Optimal conditions for Ag@AgCl/g-C 3 N 4 /TiO 2 preparation in terms of strongest photocatalysis were established by tests on Rhodamine B degradation under visible and full spectral irradiations. A good adhesion strength of the porous films on glass substrate was achieved. Stability and reusability of the films were assessed by cycling tests. Possible photocatalytic mechanisms are proposed based on the basis of trapping experiments. Systematic characterization of the film suggests that the in-situ oxidation is an effective and practical method to produce nanoscale Ag@AgCl. [ABSTRACT FROM AUTHOR]

Phase boundary engineering (PBE) has remarkably enhanced the piezoelectric properties of potassium sodium niobate {(K, Na)NbO 3 , KNN} piezoceramics, yet the physical mechanisms need to be further understood. Here we outline a new physical phenomenon to describe piezoelectricity enhancement in KNN-based ceramics with PBE. We propose that the enhancement is due to the multi-phase coexistence featured with strong relaxation behavior. The strong relaxation behavior was unambiguously revealed by cryogenic experiments and originated from the polar nanoregions (PNRs) exhibiting a scale of 2.1 nm and a weak tetragonality (c/a = 1.0040). in situ temperature-dependent experiments uncovered the thermal evolution of the ferroelectric matrix and PNRs in both unpoled and poled samples, the first report in KNN-based ceramics. Our experiments combined with phenomenological theory revealed that ultra-fine nanodomains, PNRs, and easy polarization rotation together promote macro dielectric and piezoelectric properties in the relaxation-featured multi-phase coexistence. This work reveals the physical mechanism from different levels (e.g., local-mesoscopic-macroscopic), thus providing a new systematic understanding of the observed enhancement of piezoelectricity. Proposing a new physical mechanism, relaxor-featured multi-phase coexistence, to explain piezoelectricity enhancement in potassium sodium niobate-based ceramics. [Display omitted] [ABSTRACT FROM AUTHOR]

• A new concept of tuning the trade-off between LRO and PNRs is proposed. • The concept relieves the sensitivity of d 33 and enhances temperature stability. • d 33 shows higher values at x = 0.9–0.95 and a high retention of > 83% at x = 0.8–1.1. • S uni of x = 1.1 is enhanced and has a high retention of ≥ 79% at T = 20–180 °C. To relieve the sensitivity of piezoelectric coefficient (d 33) to composition and strengthen temperature stability of strain in potassium sodium niobate {(K, Na)NbO 3 , KNN} ceramics, we proposed a new concept, tuning the trade-off between long-range ordering (LRO) and polar nanoregions (PNRs), and realized it by tailoring the content of bismuth (Bi) in an already-constructed multiphase coexistence, namely, 0.96(K 0.48 Na 0.52)(Nb 0.955 Sb 0.045)O 3 -0.04(Bi x Na 4-3 x) 0.5 ZrO 3 -0.3 mol%Fe 2 O 3 ceramics. We obtained not only the high retention of > 83% at x = 0.80–1.10 in d 33 but also higher d 33 at x = 0.90–0.95, relieving the sensitivity of d 33 to composition. We also obtained not only the enhanced strain but also the high retention of ≥ 79% over a wide temperature range of 20–180 °C at x = 1.10, irrespective of the electric field, strengthening the temperature stability. We demonstrated that high d 33 values hinge on the trade-off between LRO and PNRs, and the enhanced temperature stability of strain originates from the diffused multiphase coexistence and the reduced contribution of domain switching. Therefore, the new concept helps further design high-performance KNN-based ceramics for practical application. [ABSTRACT FROM AUTHOR]

Although the composition-driven multi-phase coexistence strategy has been widely used to modify the piezoelectric properties of potassium sodium niobate ((K, Na)NbO 3 , KNN) based ceramics, the trade-off between long-range ferroelectric ordering and chemical additives-induced disorder hinders the further improvement of piezoelectricity and makes the electric field-induced strain temperature-dependent. Herein, to resolve two issues, we proposed a new concept, that is, manipulating defect dipoles and local stress of a pre-constructed multi-phase coexistence through controlling zirconium (Zr) content. We validated the new concept by designing 0.96(K 0.4 Na 0.6)Nb 0.955 Sb 0.045 O 3 -0.04(Bi 0.5 Na 0.5)Zr (1+ x) O 3 ceramics. In samples with Zr deficiency (i.e., x =-0.1), we obtained high retention of 91% in normalized unipolar strain (S uni) over the temperature range of 30-160 °C, even under low electric fields of 10-20 kV/cm, superior to those of other representative KNN-based ceramics. In samples with slight Zr excess (i.e., x =0.07), we achieved an increase in direct piezoelectric coefficient (d 33) and converse piezoelectric coefficient (d 33 *) by 12% and 25%, respectively, in comparison with that at x =0. The enhanced temperature stability stems from the released domain walls that are pinned by defect dipoles, and the increased d 33 (and d 33 *) originates from the synergetic contributions of the multi-phase coexistence, increased grain size, and stabilization of the ZrO 2 secondary phase. Therefore, our new concept would benefit the composition design and performance improvement of KNN-based ceramics in the future. [Display omitted] [ABSTRACT FROM AUTHOR]