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A series of barium zirconate modified potassium sodium niobate-based lead-free piezoelectric ceramics [(0.97-x)(K0.45Na0.55)(Nb0.97Sb0.03)O3-0.03Bi0.5K0.075Na0.425ZrO3-xBaZrO3, KNNS–BKNZ–xBZ, x = 0 ~ 0.02] were prepared by the traditional solid-state method. The effect of BZ on the phase structure and electrical properties was systematically studied. Rhombohedral–orthorhombic–tetragonal multiphase coexistence structure can be observed for the whole ceramic system while the addition of BZ leads to the reduction in the orthorhombic phase content and increase in the rhombohedral and tetragonal phase content. At the critical composition with x = 0.01, the ceramics show the optimized electrical properties with the piezoelectric constant d33 of 265 pC/N, unipolar strain Suni of 0.168%, inverse piezoelectric coefficient d33* of 480 pm/V, room-temperature dielectric constant εr of 1634, and Curie temperature TC of 282 °C. Moreover, enhanced temperature stability was achieved in the x = 0.01 ceramics, presenting the variation of d33 less than 15% within the temperature range of 20–100 °C and the Suni remained above 80% until the elevated temperature of 175 °C. [ABSTRACT FROM AUTHOR]

In piezoceramics, the Curie temperature (TC) and piezoelectric coefficient (d33) are often inversely proportional, so it is very difficult to optimize high piezoelectricity and TC simultaneously. In addition, the high and temperature‐insensitive piezoelectric strain coefficient (d33*) with small hysteresis is also a longstanding obstacle in the development of lead‐free ceramics. In this work, a facile approach of donor doping strategy is adopted to replace Ba2+ with Yb3+, Y3+, Sm3+, and Nd3+ as a result, a high TC of 450 °C and outstanding d33 of 422–436 pC N−1 is achieved by a novel magnetic poling method. Thermally‐stable and outstanding piezoelectric strain performance (d33* ≈ 520–550 pm V−1 and ΔST ≈ 10%) with small strain hysteresis (H < 20%) results are highly encourageable in lead‐free ceramics. The main factors contributing to high piezoelectricity are the morphotropic phase boundary, suppression of defect charges by donor doping, thermal quenching, mesoscale nanodomain size, and novel poling method. The excellent piezoelectric performance and high TC of this work are superior to those of state‐of‐the‐art piezoceramics. The synergistic approaches of compositional design strategy and novel poling process in this work are highly beneficial for temperature‐insensitive piezoelectric sensor and actuator applications. [ABSTRACT FROM AUTHOR]

The apparent incompatibility between d33 and Qm in potassium sodium niobate-based lead-free ceramics is an obstacle to their applications. In this study, (K0.5Na0.5)0.98Li0.02Nb0.82Ta0.18O3 (LT-KNN) system near the orthorhombic–tetragonal (O–T) phase boundary but in the O phase region is selected as the matrix to ensure a relatively large d33 and high Tc, and help the CuO doping generate an effective "hardening" effect to improve Qm. The results show that adding proper amount of CuO into LT-KNN promotes the densification of ceramics and suppresses the abnormal grain growth, which helps to decrease the dielectric loss and obtain a high poling efficiency. Moreover, the Cu2+ doping in B-site (Nb/Ta)5+ generates oxygen vacancies ( V O ∙ ∙ ) and the Cu Nb / Ta ″ ′ - V O ∙ ∙ ′ defect dipoles could be formed, resulting an obvious "hardening" effect. With the introduction of 1 mol% CuO, the d33 increases from 82 to 180 pC/N and the Qm presents an abrupt rise from 136 to 665. More intriguingly, the addition of CuO delays the O–T phase transition while maintaining a high Tc of ~ 310 °C. Combined with the pinning effect of internal bias field, the d33 of 1 mol% CuO doped LT-KNN ceramics shows favorable stability in the wide temperature range of 20–280 °C, and a high Qm of larger than 250 can be achieved until 100 °C. Such a superior comprehensive electromechanical performance makes the ceramics promising in applications of high-power and high-frequency devices. [ABSTRACT FROM AUTHOR]

The development of lead-free ferroelectric ceramics exhibiting a high Curie point is regarded as a key aspect of improving the overall performance of high temperature sensing devices. Two-layer Dion-Jacobson phases have great potential for these applications, but the dielectric properties of many of these compounds have not been investigated and several are still erroneously considered to be non-polar. RbPrNb 2 O 7 , a two-layer Dion-Jacobson phase, has previously been identified as being non-polar at room temperature, with an orthorhombic crystal structure in space group Imma. Here, the structure of RbPrNb 2 O 7 is re-examined and its ferroelectric (FE) character confirmed through ferroelectric, dielectric and piezoelectric measurements, using dense bulk ceramics. In addition, the microstructure and phase evolution of the compound were analysed by transmission electron microscopy, variable temperature X-ray powder diffraction and differential scanning calorimetry. RbPrNb 2 O 7 is a ferroelectric at room temperature, exhibiting orthorhombic symmetry in space group I 2 cm. It undergoes a reversible FE ↔ FE phase transition at around 260 °C, with evidence for a diffuse apolar transition between 800 and 900 °C. Details of the subtle structural changes occurring at these transitions are discussed. RbPrNb 2 O 7 possesses a high Curie point of ~1090 °C, making it a potential candidate for use in high temperature piezoelectric sensing. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Lead-free piezoelectric ceramics featuring high piezoelectricity and fatigue resistance are extremely important in practical applications. In this work, 0.85Bi0.5Na0.5TiO3–0.11Bi0.5K0.5−xRbxTiO3–0.04BaTiO3 (x = 0–0.20) ceramics are developed, and the effects of Rb content on the crystalline phase, domain structure, electric property, and fatigue resistance are investigated. XRD results show that all the ceramics exhibit the rhombohedral/tetragonal morphotropic phase boundary. The introduction of Rb at A-sites induces enhanced relaxor characteristics. Increasing the Rb content leads to apparently decreased size and increased dynamics of ferroelectric domains, as revealed by the PFM and TEM observations. Notably, the fatigue resistance of ceramics is greatly improved with the introduction of Rb. In particular, the composition of x = 0.10 exhibits almost fatigue-free behaviors in conjunction with high piezoelectricity of d33 ~ 203 pC/N, which can be attributed to the formation of tweed-like nanodomains with a size of 10–20 nm and stripe-like nanodomains with an average width of ~ 3.5 nm. [ABSTRACT FROM AUTHOR]

In this work, lead-free (K 0.485 Na 0.485 Li 0.03)Nb 0.8 Ta 0.2 O 3 composition was designed to control the orthorhombic-tetragonal phases boundary near the room temperature as confirmed by Rietveld analysis, high-angle annular dark field scanning transmission electron microscopy, and temperature dependent dielectric constant. A comparative study of the direct and indirect synthesis methods was carried out and their functional properties were optimized as a function of sintering temperature (T s) and dwell time. Here, we achieved a large dynamic piezoelectric constant (d 33 *) of 510 pm/V under a very low electric field of 15–30 kV/cm. Moreover, an enhanced static piezoelectric constant (d 33) of 335 pC/N was obtained with a high Curie temperature (T C) of 315 °C. The large d 33 and d 33 * simultaneously with high T C in a single composition are promising results in lead-free polycrystalline ceramics. The strategic design of this work opens a new door for the possible development of novel functional materials for device applications. [ABSTRACT FROM AUTHOR]

Lead-free piezoelectric 0.8625NaNbO 3 -0.1BaTiO 3 -0.0375SrZrO 3 (0.8625NN-0.1BT-0.0375SZ) ceramics were prepared by templated grain growth method with NaNbO 3 templates. High orientation degree of 88.42% was achieved in the textured ceramics, which showed excellent piezoelectric performance with the quality factor Q m of 48.14 and the piezoelectric coefficient d 33 of 315 pC/N after poling. The grain morphology, crystal structure, P - E hysteresis loop, domain structures, frequency dependence of dielectric constant and loss tangent of conventional and textured 0.8625NN-0.1BT-0.0375SZ ceramics were systematically studied. It is indicated that ceramic texturing can effectively improve the piezoelectric performance of the NN-based lead-free piezoelectric ceramics, which provides a promising and broad prospect for the urgent development and practical applications of NN-based systems. • A highly oriented 0.8625NN-0.1BT-0.0375SZ textured ceramic is obtained. • The NN template excels in inducing grain growth of texture ceramics. • The dwelling time evidently affect the orientation of textured ceramics. • The texture process effectively improve the piezoelectric properties of ceramics. [ABSTRACT FROM AUTHOR]

This paper provides a detailed evaluation of the photo-piezo-catalytic properties of lead-free Ba 0.85 Ca 0.15 Zr 0.1 (Ti 1-x Co x) 0.9 (BCZT- x Co, x = 0–0.025) ferroelectric ceramics prepared by a solid-state process. By control of the Co doping level, the band gap was reduced to 2.40 eV at the composition x = 0.02, which improved the generation of photo-generated charges and enhanced the photocatalytic activity. When a solution containing BCZT-0.02Co particles was subjected to both ultrasound and illumination, the degree of degradation of Rhodamine B reached 99% within 60 min, which was grater than when subjected to illumination or ultrasound alone. Examination of the dielectric properties, photoelectrochemical measurements and band energy structure of the materials provided new insights into the catalytic mechanism, where a strong coupling between piezoelectricity and photoexcitation was clearly observed. This work therefore highlights the attractive photo-piezo-catalytic properties of BCZT- x Co doped ceramics and is the first demonstration that Co substitution in these lead-free ferroelectric ceramics provides significant potential for photo-piezo-catalysis applications. [ABSTRACT FROM AUTHOR]

In this work, fine-grained (0.95- x)(Bi 0.5 Na 0.5)TiO 3 -0.05BaTiO 3 - x Bi(Zn 2/3 Nb 1/3)O 3 (abbreviated as BNT-BT- x BZN, x = 0∼0.20) lead-free ceramics are successfully prepared, showing a high energy storage performance. The addition of BZN results in decreased grain size, enhanced breakdown strength and stronger relaxor behavior with polar nanoregions. Slimmer P - E loops are thereby achieved, leading to the improvement of energy density and efficiency. As a result, a high W D of ∼2.83 J/cm3 is achieved under a relatively low electric field of 18 kV/mm in the x = 0.125 ceramic with submicron-sized grains (∼0.4 μm). The W D value is larger than that of x = 0 ceramic by ∼800%. Furthermore, the x = 0.125 ceramic possesses excellent frequency stability and strong fatigue endurance. The BNT-BT- x BZN lead-free ceramics show promising potential for application in high energy density ceramic capacitors. [ABSTRACT FROM AUTHOR]

The energy-storage performance of stable NaNbO 3 -based antiferroelectric (AFE) ceramics was for the first time reported in (0.94- x)NaNbO 3 -0.06BaZrO 3 - x CaZrO 3 lead-free ceramics. A gradual evolution from an instable AFE phase (x ≤0.01) to an orthorhombic AFE P phase (Pbma) (0.01< x ≤0.05) was found to accompany the appearance of repeatable double-like polarization versus electric field loops although poled samples (x <0.01) own an AFE monoclinic phase (P2 1). Interestingly, compared with x ≤0.01 samples with instable antiferroelectricity, a relatively high recoverable energy storage density W rec ˜ 1.59 J/cm3 (@ 0.1 Hz) and a storage efficiency η of ˜30% were achieved in the x = 0.04 ceramic. Moreover, a high W rec of > 1.16 J/cm3 and an outstanding charge-discharge performance with fast discharge rate (t 0.9 < 100 ns) were generated in the temperature range from room temperature to 180 °C in the x = 0.04 ceramic. These results suggest that NaNbO 3 -based AFE P-phase ceramics could be new potential dielectric materials for high-energy storage capacitors. [ABSTRACT FROM AUTHOR]

The introduction of acceptor dopants into perovskites is a common method for designing hard piezoelectric ceramics by forming defect dipoles. It is interesting to find that the doping effect of a few amount of MnO 2 in (Bi 0.5 Na 0.5)TiO 3 –BaTiO 3 lead-free ceramics significantly depends on the local symmetry. A conventional hardening effect corresponding to an obviously enhanced mechanical quality factor and a decreased piezoelectric coefficient can be generated in the tetragonal phase rich zone, rather than in the rhombohedral-rich zone, where a typically amphoteric characteristic can be observed unexpectedly. The result was well interpreted by means of the formation of a local random field as a result of the local symmetry-breaking effect of point defects after doping MnO 2 in addition to a traditional internal bias field as a result of the pinning effect of defect dipoles. Compared with tetragonal-rich ones, the obviously enhanced random field in rhombohedral-rich compositions tends to induce a weakening ferroelectricity, as evidenced by composition dependent normal ferroelectric-relaxor ferroelectric phase transition. This work provides a new understanding of how charged defects affect the domain stability in the matrix with different symmetries through the competition between random electric fields and internal bias fields. • The doping effect of Mn in BNT ceramics depends on the phase structure. • An amphoteric characteristic is found in rhombohedral phase zone unexpectedly. • Both local random fields and internal bias fields are induced by charged defects. • Local random fields originate from local symmetry-breaking effect of point defects. [ABSTRACT FROM AUTHOR]

[Display omitted] • A new lead-free BiFeO 3 -BaTiO 3 is designed for piezoelectric actuator applications. • A large d 33 * ∼ 772 pm/V and thermally stable Δ d 33 *(T) ∼ 26% are achieved. • The increase in tetragonality provides polar length for B-site cation displacement. • A decrease in octahedral tilting reduces anisotropy for domain switching. • The argument of high piezoelectric strain is supported by TEM, PFM and XRD results. Designing a new high-performance lead-free ceramic has become a cutting-edge research topic due to growing concerns about the toxic nature of lead-based materials. In this work, a convenient strategy of compositional design and domain engineering is applied to the lead-fee BiFeO 3 -BaTiO 3 ceramics which provides a flexible polarization free-energy profile for domain switching. Here, simultaneously enhanced dynamic piezoelectric constant (d 33 * ≈ 772 pm/V) and a good thermal-stability (Δ d 33 * ≈ 26% over the temperature of 20–180 °C) are achieved with a high Curie temperature (T C) of 432 °C. This high piezoelectric strain performance is collectively attributed to multiple effects such as thermal quenching, suppression of defect charges by donor doping, chemically induced local structure heterogeneity, and electric field-induced phase transition. Furthermore, the addition of BT content decreased octahedral tilting that reduce anisotropy for domain switching and increased in tetragonality (c T / a T) providing a wider polar length for B-site cation displacement, leading to high piezoelectric strain performance. Atomic-resolution transmission electron microscopy and piezoelectric force microscopy combined with X-ray diffraction results strongly support the origin of high piezoelectricity. The high and temperature-stable piezoelectric strain response of this work is superior to those of other lead-free ceramics. The synergistic approach of composition design and the concept present here for the origin of high strain response provides a paradigm for the development of new materials for high-temperature piezoelectric actuator applications. [ABSTRACT FROM AUTHOR]

Abstract In this work, the crystalline phase, domain structure, and electrical properties of [Bi 0.5 (Na 0.84 K 0.16) 0.5 ] 0.96 Sr 0.04 Ti 1-x Nb x O 3 (x = 0.010–0.030) ceramics are investigated. Increasing the Nb content induces the phase transition from coexistent rhombohedral and tetragonal phases to a single pseudo-cubic phase, and the lamellar ferroelectric domains evolve into polar nanoregions. Decreased ferroelectric-to-relaxor transition temperature and enhanced frequency dispersion are found in the temperature-dependent dielectric constant and loss, implying a transition from the non-ergodic to ergodic relaxor state. The Nb substitution significantly degrades the long-range ferroelectric order with sharply decreased piezoelectric coefficients from ˜ 140 to ˜ 1 pC/N. However, a large strain of 0.32% at 5 kV/mm (normalized strain of 640 pm/V) is obtained around the critical composition of x = 0.0225. The composition of x = 0.030 shows good temperature insensitivity of the strain response, characterized by 308 pm/V with less than 15% reduction from 25 °C to 125 °C. [ABSTRACT FROM AUTHOR]

The large and temperature-insensitive piezoelectric actuator coefficient (d 33 *) with small strain hysteresis and the enhanced piezoelectric sensor coefficient (d 33) with high Curie temperature (T C) are highly demanded in the real applications. The controlled design of defects engineering has been proved to be an effective way for the improvement of temperature strain stability (Δ d 33 * (T)) and reducing hysteresis (H s) in piezoelectric ceramics. Two types of defect dipoles such as (F e Fe 3 + 2 + ′ − V O 2 − • • ) and (V Bi 3 + ''' − V O 2 − • • ) are possible in the lead-free BiFeO 3 –BaTiO 3 (BF-BT) ceramics that suppress their functional property. However, these defect dipoles can be inhibited in the Ba2+-site Sm3+-donor BF-BT engineered ceramics. Additionally, the valence and ionic radius difference of Sm3+ (1.24 Å) and Ba2+ (1.61 Å) becomes the origin of large lattice strain in the unit cell of BF-BT that leads to the maximum piezoelectric performance. Therefore, the enhanced d 33 (334 pC/N) and d 33 * (552 pm/V) with high T C (454 °C) were obtained in the Ba2+-site Sm3+-donor BF-BT lead-free ceramics. Furthermore, the reduced H s ≈ 18% and preferable temperature-insensitive piezoelectric strain, Δ d 33 * (T) ≈ 10% in the temperature 25–125 °C are highly encourageable in the lead-free ceramics. Hence, the defect dipoles controlling strategy helps to improve the functional properties and the concept presented here can be applied to design the lead-free piezoelectric material for real applications. [Display omitted] • Sm-donor/isovalent doped BiFeO 3 –BaTiO 3 quenched ceramics were synthesized. • Large d 33 = 334 pC/N and d 33 * ≈552 pm/V with high T C ≈ 454 °C were obtained. • Defects control strategy by donor doing highly improve piezoelectric strain stability. • Low strain hysteresis, H s = 18% and temperature-insensitive (≈10%) d 33 * were achieved. [ABSTRACT FROM AUTHOR]

The lead-free sodium bismuth titanate (BNT) system has been extensively investigated in the past decade due to its multi-functional electro-active properties. Here, we present a comprehensive review that encompasses the fundamentals and state-of-the-art in the development of BNT-based ceramics, with attention to the underlying composition, microstructure, and macroscopic properties. The phase structure, phase transitions, and relaxor characteristics of BNT and BNT-based solid solutions are described carefully, with a series of proposed phase diagrams. The attractive functional properties of BNT-based ceramics include piezoelectricity, electric-field-induced strain, and energy storage performance for applications in sensors, actuators, and dielectric capacitors. The focus of this review is on the microscopic origin of the macroscopic behavior, the proposed strategies for optimization of functional properties, and current challenges. Moreover, the potential applications of BNT-based ceramics in the areas of electrocaloric, oxide-ion conduction, and luminescence are briefly introduced. Finally, future perspectives are provided to highlight new and emerging research directions in this growing area. [ABSTRACT FROM AUTHOR]

There has been recently a great progress in the development of dielectric capacitors for high temperature electronic applications. The design of lead-free ceramics with high dielectric permittivity, low dielectric loss and a limited variation of these parameters over a wide temperature range is still a big challenge. In this work, lead-free Bi 0.35 Na 0.65 – 0.5x Rb 0.5x Ti 0.7 Nb 0.3 O 3 (x = 0–0.05) bulk ceramics were prepared using the solid-state reaction method. Upon Rb substitution, the variation of the dielectric permittivity was reduced substantially, in particular, at high temperature (over 200 °C). In addition, a low temperature coefficient of capacitance (TCC ≤ 10%) together with an ultra-low dielectric loss (tan δ ≤ 0.05) were achieved for the Bi 0.35 Na 0.63 Rb 0.02 Ti 0.7 Nb 0.3 O 3 sample in the temperature range from −43 °C to 292 °C. The new relaxor-type ferroelectrics also possess the outstanding stability of the dielectric properties under high DC bias voltage, which makes them promising materials for high-performance capacitors of the next generation. Unlabelled Image • Rb/Nb co-substituted Bi 0.5 Na 0.5 TiO 3 –based ceramics display TCC < 10% in the temperature range of −43 °C–292 °C. • The BNT-derived relaxors exhibit high permittivity (>800) and ultra-low dielectric loss (≤0.05) from −43 °C up to 292 °C. • The variance of the capacitance of the Bi 0.5 Na 0.5 TiO 3 –based ceramics is lower than 150 ppm under the DC voltage of 1 kV. [ABSTRACT FROM AUTHOR]