Search

Sm-doped Pb(Mg 1/3 Nb 2/3 )O 3 -0.28PbTiO 3 (PMN-0.28PT) ceramic has been reported to exhibit very large piezoelectric response ( d ~1300 pC/N) that can be comparable with PMN-0.30PT single crystal. Based on the Sm-doped PMN-0.28PT ceramics, a high frequency ultrasound transducer with the center frequency above 30 MHz has been designed and fabricated for intravascular ultrasound imaging, and the performance of the transducer was investigated via ultrasound pulse-echo tests. Further, for a porcine vessel wall, the 2D and 3D ultrasound images were constructed using signal acquisition and processing from the fabricated high-frequency transducer. The obtained details of the vessel wall by the IVUS transducer indicate that Sm-doped PMN-0.28PT ceramic is a promising candidate for high frequency transducers.33 ~1300 pC/N) that can be comparable with PMN-0.30PT single crystal. Based on the Sm-doped PMN-0.28PT ceramics, a high frequency ultrasound transducer with the center frequency above 30 MHz has been designed and fabricated for intravascular ultrasound imaging, and the performance of the transducer was investigated via ultrasound pulse-echo tests. Further, for a porcine vessel wall, the 2D and 3D ultrasound images were constructed using signal acquisition and processing from the fabricated high-frequency transducer. The obtained details of the vessel wall by the IVUS transducer indicate that Sm-doped PMN-0.28PT ceramic is a promising candidate for high frequency transducers., Competing Interests: Declaration of Conflicting InterestsThe author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

The increasing demands of device applications in harsh environments have led to higher expectations for temperature and pressure resistance in high-temperature piezoelectric materials. In order to understand the performance characteristics of BiScO3-PbTiO3 (BS-PT) high-temperature piezoelectric materials in practical device applications, this study focuses on analyzing the dielectric, piezoelectric, and ferroelectric properties of BS-64PT ceramics under uniaxial stress up to 150 MPa, as well as its electromechanical performance under a hydrostatic pressure of up to 400 MPa. As the uniaxial pressure increases, both the bias-field and large-signal piezoelectric coefficients exhibit a pattern of initially increasing and subsequently decreasing. Furthermore, the bias-field piezoelectric coefficient exceeds 450 pC/N and the large-signal piezoelectric coefficient surpasses 630 pC/N under uniaxial pressures below 100 MPa. This highlights their exceptional resistance to depolarization caused by uniaxial stress. To obtain more precise piezoelectric properties for BS-64PT ceramics in the 31 and 33 modes under hydrostatic pressure, the admittance fitting method was utilized. This method takes into account the significant losses at higher pressures. Within the pressure range of 0–400 MPa, the values of d33 and d31 for BS-64PT ceramics exhibited a minor change of 7.6% and 8%, respectively. These findings indicate that BS-64PT ceramics exhibit more stable piezoelectric properties under both uniaxial and hydrostatic pressures when compared to the majority of Pb-based perovskite-structured materials. The exceptional stability of piezoelectric properties in BS-PT ceramics can be primarily attributed to their elevated anisotropy energy or coercivity field compared to other perovskite-structured Pb(Mg1/3Nb2/3)O3 (PMN) / Pb(Zr,Ti)O3 (PZT)-based ceramics reported. [ABSTRACT FROM AUTHOR]

(K,Na)NbO3(KNN)-based ceramics are a promising lead-free piezoelectric material that could replace Pb(Zr1−xTix)O3-based materials due to their higher Curie temperature and superior electrical properties. However, the volatilization of sodium and potassium during conventional high-temperature sintering makes it difficult to obtain KNN ceramics with a dense structure and excellent electrical properties. Herein, a conventional solid-phase method combined with microwave sintering is applied for the preparation of KNN ceramics. The influence of the microwave sintering process on the microstructure and electrical properties of KNN ceramics were studied. The optimal microwave sintering conditions for KNN ceramics were determined to be 1100°C for 50 min. Under these conditions, the ceramic samples exhibited excellent ferroelectric properties, with the maximum polarization (Pmax) of 20.4 μC/cm2 and a remanent polarization (Pr) of 18.1 μC/cm2. Additionally, the samples demonstrated impressive piezoelectric properties, including the maximum electric field-induced strain (Smax) of 0.0251%, a dynamic piezoelectric coefficient (d33*) of 125.5 pm/V, and a piezoelectric coefficient (d33) of 109.8 pC/N. The study has important implications for the use of microwave sintering to achieve the densification of the ceramic with volatile elements such as KNN-based ceramics at lower sintering temperature and short sintering time. [ABSTRACT FROM AUTHOR]

Piezoelectric ceramics with high electro strain are widely used in actuators, sensors, and so on. Here, this work investigates the electro strain of representative piezoelectric materials, and analyzes the influence of electrode type on the electro strain of PZT41 with significant strain anomalies. It is found that the occurrence of abnormally significant strain is not affected by the electrode but caused by intrinsic defects. Therefore, the ceramic samples with and without defects tailoring in Na 0.5 Bi 0.5 TiO 3 (NBT) based and PbZr 0.52 Ti 0.48 O 3 (PZT) based systems were prepared by the solid-state reaction method, and the results show that abnormally ultrahigh electro strains occur in excessively thin samples with diploes due to defects tailoring. Through displacement configuration experiments and comprehensive analysis of polarization switching processes, it is found that the occurrence of asymmetric abnormal significant strains is caused by reversible bending deformation in excessively thin samples. This work provides new support for the emergence of ultrahigh electro strain in piezoelectric ceramics. [ABSTRACT FROM AUTHOR]

Environment-friendly lead-free potassium sodium niobate-based piezoelectric materials have been widely used in acoustic device applications because of its high piezoelectric response, high Curie temperature, and low acoustic impedance. In our previous works, samarium modified 0.915(K0.45Na0.5Li0.05)NbO3–0.075BaZrO3–0.01(Bi0.5Na0.5)TiO3 (Sm–KNLN–BZ–BNT) ceramics have achieved high piezoelectric properties with good thermal stability. To further improve its properties and thermal stability, grain orientation-controlled methods have been introduced to Sm–KNLN–BZ–BNT ceramics. In this work, textured Sm–KNLN–BZ–BNT ceramics with a 93% ⟨001⟩c-oriented textured degree have been prepared. The samples have achieved a d33* value with 532 pm/V and better thermal stability between room temperature to 150 °C than the non-textured samples. Moreover, ultrasonic transducers with a 25 MHz center frequency have been designed and fabricated by the textured Sm–KNLN–BZ–BNT ceramics. The peak-to-peak of the transducers has reached a 1.78 V high level, which demonstrated the textured Sm–KNLN–BZ–BNT ceramics are a good candidate for acoustic applications. [ABSTRACT FROM AUTHOR]

Flexoelectric effect possesses potential applications in electromechanical conversion, and the flexoelectric coefficient of ferroelectrics is greatly larger than that of ordinary dielectrics. Among the ferroelectrics, BaTiO 3 (BT) ceramics are lead-free materials, also receive a high flexoelectric response. However, it is still inferior to the piezoelectric response of lead-based piezoelectric materials. Herein, we inhomogeneously added x wt. % ZrO 2 into BT ceramics (x wt. % ZrO 2 /BT ceramics, and x = 0.05, 0.5, 1, 2) to enhance the flexoelectric response of BaTiO 3 -based ceramics. The largest effective flexoelectric coefficients (μ ρ) of ∼800 μC/m at room temperature (RT) and ∼1500 μC/m near Curie temperature (T C ∼ 127 °C) were obtained in 0.5 wt % ZrO 2 /BT ceramics, which is ∼6.7 times and ∼3.9 times larger than that of the as-prepared BT ceramics at RT and near T C (∼131.7 °C here) respectively. Although T C of the 0.5 wt % ZrO 2 /BT ceramics decreases compared with that of BT ceramics, its higher μ ρ than that of the as-prepared BT ceramics maintains a wide temperature range, extending to 160 °C. The enhancement of the μ ρ of the 0.5 wt % ZrO 2 /BT ceramics is largely attributed to the compositional heterogeneity between grain boundaries gathered with irregular paraelectric and orthorhombic Ba(Zr, Ti)O 3 , and grains which are tetragonal BaTiO 3. The compositional heterogeneity is easily shaped into a strain gradient (namely a flexoelectric polarization), which plays a promoting effect on the flexoelectric coefficients. [ABSTRACT FROM AUTHOR]

The piezoelectric and electromechanical coupling coefficients in conjunction with their temperature stability are the crucial figure-of-merits of piezoelectric materials, due to these properties determine their response sensitivity and operating temperature range, respectively for practical applications. In this work, Sb, (Bi 0.5 Na 0.5)ZrO 3 , and (Bi 0.5 K 0.5)HfO 3 were used to regulate phase transition of KNN-based ceramics, and resultant large piezoelectric constants d 33 ∼ 430 ± 10 pC/N, unipolar strain S uni ∼ 0.18 % at 40 kV/cm, and a high planar electromechanical coupling factor k p ∼ 55 % were observed in the composition with rhombohedral-orthorhombic-tetragonal (R-O-T) multiphase coexistence. Ex-situ electric field XRD measurement and TEM observation indicate the outstanding piezoelectric properties are originated from the electric field-induced phase transition, nanodomains and polar nanoregions, which lower polarization anisotropy and facilitate polarization rotation between different crystallographic symmetries. In addition, the piezoelectric properties of the samples with R-O-T phases coexistence show superior temperature stability and fatigue resistance after 106 bipolar electric cycles. The present study not only helps to understand the structural origin of high piezoresponse, but also lays a foundation for the applications of KNN-based ceramics. [ABSTRACT FROM AUTHOR]

The ferroelectric domain plays an important role in determining the piezoelectric performance of ferroelectric ceramics. Herein, LiNbO 3 (LN) is used as an additive to tune the ferroelectric domain of 0.49Pb(Ni 1/3 Nb 2/3)O 3 -0.2Pb(In 1/2 Nb 1/2)O 3 -0.31PbTiO 3 (PNN-PIN-PT) ceramics. PNN-PIN-PT-0LN ceramic exhibits the ordered tetragonal phase (90 °) domain wall and rhombohedral phase (71 ° and 109 °) domain wall. Incorporating LN into the system leads to the transformation of the majority of structured macro-domains into random micro-domains with smaller sizes, which disrupt their long-range ordered ferroelectric domains, resulting in significant piezoelectric enhancement. Compared to PNN-PIN-PT-0LN ceramics, PNN-PIN-PT-1.8LN ceramics exhibit giant piezoelectric responses with d 33 = 1112 pC/N, d 31 =521 pC/N, d 33 * =1220 pm/V (@ E = 5 kV/cm), ε r = 12092. These findings shed light on a specific aspect of domain engineering in piezoelectric materials, thus contributing to a more comprehensive understanding of the underlying factors that give rise to the phenomenon of giant piezoelectricity. [ABSTRACT FROM AUTHOR]

Granite is a common engineering material that exhibits complex mechanical properties under external loads. This study conducted experimental research and analysis in conjunction with the active monitoring technology of piezoelectric ceramics. A quantitative analysis method for the mechanical properties of rock materials based on piezoelectric health monitoring was established, and for the first time, the piezoelectric monitoring results of rock were mapped and compared with the uniaxial compression performance indicators of rock. In this study, two sets of cyclic impact experiments were conducted on granite samples using a drop hammer. The piezoelectric signals of the granite samples were detected using piezoelectric ceramic active sensing technology. A piezoelectric ceramic damage monitoring method was proposed, and the damage factor of the granite samples was calculated using the wavelet packet energy method. Subsequently, uniaxial compression experiments were performed on the damaged granite samples to obtain mechanical performance data. Finally, a mathematical relationship model was established between the piezoelectric signal and the uniaxial compressive strength of the rocks. It was found that the damage factor of the piezoelectric monitoring signal of the damaged rock were linearly related to the uniaxial compressive strength of the damaged rock. [ABSTRACT FROM AUTHOR]

Dense (Pb0.92Ba0.08)Nb2O6‐xmol% MnO2 with 0.25 wt% TiO2 ceramics with a single orthorhombic phase were synthesized through a conventional solid‐state reaction method. Excellent piezoelectric performance (d33 = 90 pC/N) and low dielectric loss (tan δ = 0.5%) are achieved in Mn‐doped samples. Interestingly, the dielectric anomalies are observed in the temperature range of 300–400°C, which could be completely suppressed through Mn doping. The dielectric anomalies are associated with thermally activated domain wall motion, which could be constrained by the defect dipoles produced by Mn doping. More importantly, all samples experience about 12% performance degradation below 300°C, attributed to an accelerated aging process at elevated temperatures. After thermal aging, the samples exhibit excellent performance stability within the temperature range of 25–450°C, showing no further degradation. The results indicate that the PbNb2O6‐based ceramics are promising high‐temperature piezoelectric materials for piezoelectric devices operating at temperatures up to 450°C. [ABSTRACT FROM AUTHOR]

Piezoelectric temperature stability is often a very important item for piezoelectric materials when putting them into practical applications like filters and ultrasonic transducers. Phase transitions of (K,Na)NbO 3 -based compositions that contain neither toxic Pb nor Sb elements were tailored to simultaneously acquire enhanced piezoelectric properties and good piezoelectric temperature stability in this study. Specifically, dense 0.94(K 0.48 Na 0.52)NbO 3 -0.03BaZrO 3 -0.01BaSnO 3 -0.02(Bi 0.5 Na 0.5)ZrO 3 ceramic and its further compositionally modified one by 1 wt% MnO 2 were prepared. Both of these two ceramics display quite weak piezoelectric temperature dependence in the usage temperature range between −30 °C–100 °C, but the one modified by MnO 2 has the significantly improved piezoelectric properties with a high piezoelectric coefficient d 33 of 310 pC/N and large electromechanical coupling factors k p and k 33 of 0.57 and 0.73 at room temperature. The obtained excellent piezoelectric performance is considered to be associated closely with the stable piezoelectric characteristic of the orthorhombic phase and the diffused rhombohedral-orthorhombic and orthorhombic-tetragonal phase transitions. [ABSTRACT FROM AUTHOR]

Piezoelectric materials are used for various commercial and strategic applications. For most of the current generation applications the usage temperature is about 150°C and therefore, ceramics like lead zirconate titanate or lead-free ceramics such as potassium sodium niobite which exhibit Curie temperature (TC) in between 350° and 450°C are useful. However, in the next-generation applications, the usage temperature is expected to be more than 500°C. As a thumb rule usage temperature of a ferroelectric ceramic is ½ of TC and hence, ceramics with a TC greater than 1000°C are required for such applications. Perovskite layer structure (PLS) piezoceramics exhibit TC well above 1000°C and thus, are the most promising materials for high temperature piezoelectric applications. With this background, we review the synthesis, fabrication and structural aspects of the PLS piezoceramics. We also discuss the peculiar microstructure and dielectric properties of these ceramics along with their advantages and limitations. [ABSTRACT FROM AUTHOR]

Currently, in the modification methods of K0.5Na0.5NbO3(KNN) ceramics to enhance their piezoelectric performance, key parameters such as Curie temperature are usually sacrificed. However, this trade-off limits the practical application of piezoelectric materials. Thus, addressing the trade-off between different performance parameters of piezoelectric ceramics becomes a major challenge.The present research employs the conventional solid phase sintering process and utilizes controlled doping of (Bi0.5Li0.5)0.9Sr0.1ZrO3 to regulate the ceramic system, K0.44Na0.55Ag0.01Nb0.95Ta0.05O3, at its polycrystalline phase boundary, thereby achieving a trade-off between performance. The ceramic samples of the system formed a compact solid solution with a single-phase perovskite structure and formed orthorhombic-tetragonal and rhombohedral-tetragonal polycrystalline phase boundaries at 0.02 ≤ x ≤ 0.03 and 0.035 ≤ x ≤ 0.06, respectively, according to XRD, SEM, and EDS analysis. The electrical properties test results show that in the multiphase coexisting region of x = 0.035, the ceramics of the system show excellent electrical properties, respectively d33 = 312 pC/N, kp = 46.5%, εr = 1019, tanδ = 3.78%, Pr = 20.08 μC/cm2, Ec = 12.97 kV/cm, and TC = 342 ℃. These results show that the properties of the system ceramics have reached a relatively high level, which provides an effective strategy for the practical application of piezoelectric ceramics. [ABSTRACT FROM AUTHOR]

A typical piezoelectric energy harvester is a bimorph cantilever with two layers of piezoelectric material on both sides of a flexible substrate. Piezoelectric layers of lead-based materials, typically lead zirconate titanate, have been mainly used due to their outstanding piezoelectric properties. However, due to lead toxicity and environmental problems, there is a need to replace them with environmentally benign materials. Here, our main efforts were focused on the preparation of hafnium-doped barium titanate (BaHfxTi1−xO3; BHT) sol–gel materials. The original process developed makes it possible to obtain a highly concentrated sol without strong organic complexing agents. Sol aging and concentration can be controlled to obtain a time-stable sol for a few months at room temperature, with desired viscosity and colloidal sizes. Densified bulk materials obtained from this optimized sol are compared with a solid-state synthesis, and both show good electromechanical properties: their thickness coupling factor kt values are around 53% and 47%, respectively, and their converse piezoelectric coefficient d 33 ∗ values are around 420 and 330 pm/V, respectively. According to the electromechanical properties, the theoretical behavior in a bimorph configuration can be simulated to predict the resonance and anti-resonance frequencies and the corresponding output power values to help to design the final device. In the present case, the bimorph configuration based on BHT sol–gel material is designed to harvest ambient vibrations at low frequency (<200 Hz). It gives a maximum normalized volumetric power density of 0.03 µW/mm3/Hz/g2 at 154 Hz under an acceleration of 0.05 m/s2. [ABSTRACT FROM AUTHOR]

Lead Zirconium Titanate (PZT) is a potential piezoelectric material for sensor and transducer applications due to its outstanding piezoelectric coupling near the morphotropic phase boundary (MPB). This is because PZT can switch between tetragonal and rhombohedral phases. PZT is still considered to be one of the piezoelectric materials that has received the greatest amount of attention from researchers and is used the most frequently. Modification with Lithium will improve the piezoelectric properties. In this study, the structural properties and morphological studies of Lead zirconium titanate and Lead zirconium titanate with Lithium modification have been evaluated. Various Scherrer's models and other models, such as the Williamson-Hall model and Size-strain plots model, were used to display the observed fluctuations in crystallite size. Morphological analysis was used to determine the particle size. Graphs showing the distribution of particle sizes were drawn. [ABSTRACT FROM AUTHOR]

The ultrahigh piezoelectric coefficient (d 33 ≥ 1000 pC/N) exhibited by piezoelectric Pb(Zr,Ti)O 3 (PZT) ceramics not only captivates researchers but also holds considerable practical value across various applications. While significant progress has been made in enhancing piezoelectricity of PZT-based ceramics, novel mechanisms need to be proposed to explain the piezoelectric behavior of new systems with ultrahigh d 33. In this study, we initially employ LiNbO 3 as an additive to enhance the piezoelectric properties of the Pb(Ni 1 / 3 Nb 2 / 3)O 3 –PbZrO 3 –PbTiO 3 ceramics. and the optimal performance is achieved by incorporating 1.5 mol% of LiNbO 3 into the system, resulting in an ultrahigh d 33 ∼1178 pC/N (d 33 * ∼1560 p.m./V (@ E = 5 kV/cm)). The corresponding mechanism for this superior piezoelectric response involves the AB-site co-doping effect, especially the (Li Pb ′ − Nb Zr / Ti ∙) defect dipoles formed by the introduction of LiNbO 3. In particular, the addition of LiNbO 3 leads to a more uniform distribution of domain sizes, thereby further enhancing the ultrahigh piezoelectricity. These findings pave the way for a deeper under-standing of the origin of ultrahigh piezoelectric properties and make substantial contributions to the advancement of piezoelectric materials for practical applications in electromechanical devices. [ABSTRACT FROM AUTHOR]

Potassium sodium niobate (KNN) is an environmentally compatible piezoelectric material for substituting harmful lead-based ceramics. KNN-based ceramics have excellent piezoelectric properties with high Curie temperature. But, KNN faces difficulties during the processing like volatilization of alkali elements, chemical inhomogeneity, low densification, etc. The objective of this research is to investigate the impact of certain metal oxides additions like ZnO and MnO2 as sintering aids to solve the problems of the preparation and hence study the structural and electric properties of K0.5N0.5NbO3 (KNN) ceramics. ZnO and MnO2 added potassium sodium niobate, K0.5N0.5NbO3 was prepared by using the ceramic method. The prepared samples were sintered at 1000 °C for 2h conventionally. The structural properties of the ceramics have been analyzed by using X-Ray Diffractometer. The study demonstrates the formation of the orthorhombic-symmetric perovskite phase in all the prepared samples. The microstructural behavior of the ceramics has been characterized by techniques such as scanning electron microscopy (SEM) and compositional properties were studied by energy dispersive x-ray (EDAX). The effects of metal oxide additions on the electronic properties such as dielectric constant, dielectric loss, impedance properties, Nyquist plot, etc., were studied. The results have been analyzed and discussed in the paper. [ABSTRACT FROM AUTHOR]

BiFeO3–SrTiO3 (BF–ST) ceramics have been considered a novel class of lead‐free dielectric materials exhibiting notable dielectric constants and remarkable thermal stability. In this work, we fabricated a series of (1 − x)BF–xST (0.32 ≤ x ≤ 0.44) ceramics near the morphotropic phase boundary and comprehensively investigated their microstructure and electrical properties, which seeks to optimize the piezoelectric performance. As the ST content increases, a gradual reduction in the rhombohedral phase fraction is observed alongside a corresponding increase in the cubic phase fraction. Although x = 0.38, the maximum grain size of 5.66 μm is obtained, accompanied by a distinctive heterogeneous core–shell microstructure, which demonstrates a high remanent polarization of 51.2 μC/cm2 and a maximum d33 value of 72 pC/N. Furthermore, impedance spectroscopy analysis reveals the formation of a conductive core and a nonconductive shell within the sample. These findings highlight the potential of optimized BF–ST ceramics as promising alternatives to lead‐based piezoelectric materials, offering exceptional ferroelectric and piezoelectric properties. [ABSTRACT FROM AUTHOR]

Design of a projecting‐receiving dual‐purpose transducer is challenging due to the difficulty of synthesizing piezoelectric materials with combinatory "soft" properties (high piezoelectric coefficient d) and "hard" properties (low dielectric loss and high mechanical quality factor Qm). In this study, we provide a different perspective to address this challenge via exploiting single‐crystal‐like electrostriction coefficient Q33 through the fabrication of grain oriented or textured "hard" piezoelectric ceramics. Mn‐doped 0.27Pb(In1/2Nb1/2)O3–0.41Pb(Mg1/3Nb2/3)O3–0.32PbTiO3 (Mn:PIN–PMN–PT) piezoelectric ceramics with a high [0 0 1]c texture fraction of 99% were synthesized, which exhibit three times greater piezoelectric properties (d33 ∼ 828 pC/N) than random counterparts (d33 ∼ 251 pC/N), while maintaining low loss (tan δ ∼ 0.5%, Qm = 443). According to the formula d33=2Q33Prε33${d}_{{\mathrm{33}}}{\mathrm{\ = \ 2}}{Q}_{{\mathrm{33}}}\ {P}_{\mathrm{r}}\ {\varepsilon }_{{\mathrm{33}}}$, the large improvement of d33 in textured ceramics is mainly due to a doubling increase in dielectric constant ε33 and Q33 (∼0.057 m4/C2). Notably, the Q33 exhibits remarkable similarity to that of PMN–PT single crystals, further contributing to the enhanced piezoelectric performance of textured ceramics. Phase field model of ferroelectrics was performed to understand the texturing on Q33 and elucidate the underlying mechanism at the domain level. The textured ceramics exhibit excellent combinatory "soft" and "hard" properties, which are the promising materials for developing projecting‐receiving dual‐purpose transducers with high efficiency and high sensitivity. [ABSTRACT FROM AUTHOR]

Piezoelectric ceramic and polymeric separators have been proposed to effectively regulate Li deposition and suppress dendrite growth, but such separators still fail to satisfactorily support durable operation of lithium metal batteries owing to the fragile ceramic layer or low‐piezoelectricity polymer as employed. Herein, by combining PVDF‐HFP and ferroelectric BaTiO3, we develop a homogeneous, single‐layer composite separator with strong piezoelectric effects to inhibit dendrite growth while maintaining high mechanical strength. As squeezed by local protrusion, the polarized PVDF‐HFP/BaTiO3 composite separator generates a local voltage to suppress the local‐intensified electric field and further deconcentrate regional lithium‐ion flux to retard lithium deposition on the protrusion, hence enabling a smoother and more compact lithium deposition morphology than the unpoled composite separator and the pure PVDF‐HFP separator, especially at high rates. Remarkably, the homogeneous incorporation of BaTiO3 highly improves the piezoelectric performances of the separator with residual polarization of 0.086 μC cm−2 after polarization treatment, four times that of the pure PVDF‐HFP separator, and simultaneously increases the transference number of lithium‐ion from 0.45 to 0.57. Beneficial from the prominent piezoelectric mechanism, the polarized PVDF‐HFP/BaTiO3 composite separator enables stable cyclic performances of Li||LiFePO4 cells for 400 cycles at 2 C (1 C = 170 mA g−1) with a capacity retention above 99%, and for 600 cycles at 5 C with a capacity retention over 85%. [ABSTRACT FROM AUTHOR]

Among the lead-free piezoceramics, (1 − x)BiFeO 3 − x BaTiO3 (BF-BT) is considered a promising candidate for high-temperature piezoelectric materials owing to its high Curie temperature ( T C > 4 0 0 ∘ C) and good electromechanical properties. In this work, the hydrothermal synthesis method was used to prepare the precursor powders of BiFeO3 and BaTiO3, and then the mixed powder compacts with the chemical composition of 0.7BF–0.3BT were sintered under pressureless conditions. The influence of the hydrothermal reaction times (12–24 h) of BiFeO3 on the structures and electric properties of the sintered ceramics was instigated. First, all the samples synthesized with the tetragonal BaTiO3 and BiFeO3 powders were identified with relatively stable dielectric properties. As the hydrothermal reaction time to synthesize BiFeO3 increased, the dielectric properties as well as the temperature stability of the 0.7BiFeO3–0.3BaTiO3 ceramics also improved. At the condition of a hydrothermal reaction time of 24 h, the sample obtained possesses both the lowest temperature coefficient of dielectric constant (T k ε = 1. 5 3 × 1 0 − 2 / ∘ C between RT and 3 0 0 ∘ C) and the highest Curie temperature ( T C = 4 7 1 ∘ C at 100 kHz). Moreover, at high temperatures, it exhibits a higher AC impedance than others. The calculating result based on the resistive constant-phase-element model (R-CPE) circuit model showed that the grain boundary of the 0.7BF–0.3BT ceramics contributes more resistance to the conductivity at high temperatures. In summary, the hydrothermal reaction proved to be a useful way that achieves the preparation of single-phase 0.7BF–0.3BT ceramics with improved electrical properties. [ABSTRACT FROM AUTHOR]

Copyright of Piezoelectrics & Acoustooptics is the property of Piezoelectric & Acoustooptic and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Next generation advanced piezoelectric transducers significantly rely on lead-free piezoelectric ceramics. Previous investigations have indicated that defect engineering by acceptor doping is a preferable approach to customize piezoelectric materials, but this method leads to a trade-off between d 33 and the electromechanical qualities (Q m , k p , etc.), which make the collaborate modulation to be a great challenge. In this work, a novel synergistic modulation combing heterovalent-ion donor doping and oxygen-vacancy regulation is proposed to achieving preferably balanced piezoelectric properties. Herein, (K 0.5 Na 0.5) 1-x Ca x NbO 3 ceramics (abbreviated as 100xKNCN) are prepared based on a solid-state reaction method, and the effects of electromechanical properties of potassium sodium niobate (KNN) ceramics are regulated by defect dipoles and oxygen vacancies. The results elucidate that an appropriate quantity of Ca ion doping could construct a rhombohedral-tetragonal (R–O) phase boundary, which is beneficial to the improvement of d 33 and Q m. Furthermore, a preferably balance of electromechanical qualities and piezoelectric coefficient is realized by annealing the sample in N 2 atmosphere (2KNCN/N 2). Compared with 2KNCN, the d 33 and Q m of 2KNCN/N 2 increase by approximately 30% and 41%, respectively. This work is expected to provide an effective paradigm to develop defect engineering and make it a promising candidate for industrial piezoelectric application. [ABSTRACT FROM AUTHOR]

In the first part, a means to synthesize high‐density homogeneous (K,Na)NbO3 (KNN) ceramics with high piezoelectric performance and chemical stability at low spark‐plasma sintering temperature was found. However, these properties could not be obtained reproducibly, thus this second part is focused on solving this issue. Here, instead of doing a fine pulverization of raw materials prior to the reaction, the powders are ultimately mixed in the molten state and quenched to keep a single stoichiometry. A fast quenching is found to promote a better homogenization of the KNN phase upon annealing. Additionally, the coarse‐ground KNN powder is pre‐annealed before fine pulverization to preserve its high crystallinity. This innovative procedure prevents the formation of parasitic phases, leading with it to high‐performance undoped KNN ceramics (d33 ≈ 145 – 154 pC/N, kp ≈ 47–48% and kt ≈ 35 – 42%), while achieving both high reproducibility and chemical stability. [ABSTRACT FROM AUTHOR]

(K,Na)NbO3‐based compounds are attracting much attention for their high potential as Pb‐free piezoelectric ceramics. They have, however, three major drawbacks to overcome in order to achieve a mature development: densification, reproducibility, and chemical stability. In this first part, based on standard solid‐state reaction, the way to synthesize high‐density homogeneous ceramics with high piezoelectric performance and chemical stability is elucidated. It relies on a low‐temperature spark‐plasma sintering process, after the raw materials have been finely pulverized prior to reaction. The reproducibility, however, remains a pending issue due to the unavoidable random formation of parasitic phases. [ABSTRACT FROM AUTHOR]

As legislative restrictions on the use of hazardous lead-containing materials are approaching and the demand for environmentally-benign piezoelectric materials continues to grow, there is an urgent need for viable lead-free piezoelectric alternatives. (K,Na)NbO 3 (KNN)-based ceramics are environmentally-friendly, however, their piezoelectric properties still fall short of those of commercial lead-based ceramics. Herein, we report an alternative KNN material with the composition of (100- x)(K 0.49 Na 0.49 Li 0.02)(Nb 0.8 Ta 0.2)O 3 - x BaZrO 3 + 2 wt % MnO ceramics prepared by a conventional solid-reaction approach. The addition of BaZrO 3 produces finer domains and thus improves the piezoelectric and dielectric properties. MnO acts as sintering aid to reduce alkaline elements volatilization by lowering the sintering temperature. The mitigated volatilization of alkaline elements significantly reduces the concentration of oxygen vacancies, and thus contributes to enhanced piezoelectric properties. An optimal normalized strain (d 33 *) up to 476 pm/V at room temperature with a low driving electric field of 1.5 kV/mm is achieved at x = 4. More encouragingly, the ceramics also possess excellent temperature stability and fatigue resistance. [ABSTRACT FROM AUTHOR]

One of the recent innovations in the field of personalized healthcare is the piezoelectric nanogenerators (PENGs) for various clinical applications, including self-powered sensors, drug delivery, tissue regeneration etc. Such innovations are perceived to potentially address some of the unmet clinical needs, e.g., limited life-span of implantable biomedical devices (e.g., pacemaker) and replacement related complications. To this end, the generation of green energy from biomechanical sources for wearable and implantable bioelectronic devices gained considerable attention in the scientific community. In this perspective, this article provides a comprehensive state-of-the-art review on the recent developments in the processing, applications and associated concerns of piezoelectric materials (synthetic/biological) for personalized healthcare applications. In particular, this review briefly discusses the concepts of piezoelectric energy harvesting, piezoelectric materials (ceramics, polymers, nature-inspired), and the various applications of piezoelectric nanogenerators, such as, self-powered sensors, self-powered pacemakers, deep brain stimulators etc. Important distinction has been made in terms of the potential clinical applications of PENGs, either as wearable or implantable bioelectronic devices. While discussing the potential applications as implantable devices, the biocompatibility of the several hybrid devices using large animal models is summarized. This review closes with the futuristic vision of integrating data science approaches in developmental pipeline of PENGs as well as clinical translation of the next generation PENGs. Piezoelectric nanogenerators (PENGs) hold great promise for transforming personalized healthcare through self-powered sensors, drug delivery systems, and tissue regeneration. The limited battery life of implantable devices like pacemakers presents a significant challenge, leading to complications from repititive surgeries. To address such a critical issue, researchers are focusing on generating green energy from biomechanical sources to power wearable and implantable bioelectronic devices. This comprehensive review critically examines the latest advancements in synthetic and nature-inspired piezoelectric materials for PENGs in personalized healthcare. Moreover, it discusses the potential of piezoelectric materials and data science approaches to enhance the efficiency and reliability of personalized healthcare devices for clinical applications. [Display omitted] [ABSTRACT FROM AUTHOR]

Reducing mechanical losses and suppressing self‐heating are critical characteristics for high‐power piezoelectric applications. For environmentally friendly Pb‐free piezoelectric ceramics, traditional acceptor doping or annealing treatments have successfully improved the mechanical quality factor (Qm) based on a ceramic matrix with a poor piezoelectric coefficient (d33<100 pC/N). Nevertheless, a ceramic with high Qm and d33 values has not been reported owing to the inverse relationship between Qm and d33. Herein, a novel hardening method called grain boundary diffusion is used to develop Pb‐free potassium sodium niobate ceramics, where Qm increased by more than two‐fold (from 51 to 132) and a high d33 value (d33 = 360 pC/N) is maintained. Significantly, d33 retained 98% of its initial value after 180 days, exhibiting improved aging stability. The established properties are associated with the formation of the core‐shell microstructure and the full gradient composition distribution using structural characterizations and phase‐field simulations, where the core maintains a high d33 and the shell provides a hardening effect. The novel hardening effect in piezoelectric materials, known as grain boundary diffusion hardening, highlights the enhancement of the mechanical quality factor with high piezoelectricity, providing a new paradigm for the design of functional materials. [ABSTRACT FROM AUTHOR]

As a promising lead-free high-temperature piezoelectric material, BiFeO 3 –BaTiO 3 (BF-BT) is still under debate on its crystal structure, especially for the compositions in the morphotropic phase boundary (MPB). Herein, the crystal structure of (1- x)BF- x BT ceramics near the MPB with x = 0.20–0.33 was analyzed by X-ray diffraction and Raman spectroscopy. With the addition of BT, the phase transition from distorted rhombohedral to pseudo-cubic structure was determined by Rietveld refinement. Raman analysis showed the weakening interactions between the A-site cations and BO 6 octahedron, as well as the degenerated distortions of BO 6 octahedron. Intriguingly, the results of X-ray photoelectron spectroscopy suggested the inhibition of Fe3+ reduction and decrease in oxygen vacancy concentration by the incorporation of BT. In terms of the electrical properties, the significant decline in Curie temperature, improvement in permittivity, and reduction in high-temperature dielectric loss can be observed with the increase of BT content. The increased remnant polarization, enhanced dielectric response and decreased coercive field were helpful for the piezoelectric performance. The maximum room-temperature piezoelectric coefficient of ∼160 pC/N and high-temperature piezoelectric coefficient of ∼324 pC/N were acquired in the x = 0.30 ceramics. This work provides a clear scope for further research on the structural transformation and high-temperature piezoelectric applications of BF-BT system. [ABSTRACT FROM AUTHOR]

In harsh environments, the piezoelectric devices with critical component of high-temperature piezoelectric materials are in great demand. BiScO 3 -PbTiO 3 ceramics with large piezoelectric coefficient (d 33) and high Curie temperature (T c), shows a high-level dissipation factor (tanδ), causing serious self-heating. Here, a multiple-level approach, that is, regulation of phase and domain structures, domain pinning by isolated defects, and enlargement of the activation energy, is proposed to achieve a well-balanced piezoelectric performance. Based on this strategy, novel BiScO 3 -PbTiO 3 -(Sr 0.7 Bi 0.2)TiO 3 +MnO 2 ceramics (Mn:BS-PT-SBT) were fabricated. Among them Mn:BS-0.62PT-0.03SBT displays an ultralow tanδ of 1.62% at 200 °C, a large d 33 of 358 pC N−1, and a high T c of 425 °C. Moreover, the fabricated acoustic emission sensor maintains a high amplitude of 99 dB within 25–200 °C, and the emission transducer has a large residual power ratio twice that of commercial P-5 G at 200 °C. This study provides an effective route for designing piezoelectric ceramics that operate competitively at high temperatures. [ABSTRACT FROM AUTHOR]

With the rapid growth to design and engineer the smart and efficient electronic devices like piezoelectric sensors, the surge for the materials with multifunctional properties have risen tremendously. Herein, a morphotropic phase boundary (MPB) existent 0.94(Bi 0.5 Na 0.5 TiO 3)-0.06BaTiO 3 (BNBT) ceramics have been fabricated and the influence of additive MnO 2 (0–0.20 wt%) has been examined, via structural, morphological, ferroelectric and dielectric analysis. Keeping the MPB region stable, BNBT:0.15Mn ceramic has shown the much improved results with remnant polarization (P r) of 38.72 μC/cm2, piezoelectric coefficient (d 33) of 211 pC/N, and dielectric constant (ϵ r) of 4502, sample has maintained its stable d 33 value (198 pC/N) till 200 °C. Moreover, the dielectric constant dependence on temperature analysis has been observed to analyze the Curie temperature (T C) of the samples, where BNBT:0.15Mn ceramic has exhibited the T C of ∼335 °C, which is the main reason of achieving the stable piezoelectric effect till 200 °C. Present study not only provides the new direction for the material engineering but also demonstrates the potential of the reported material for high-temperature piezoelectric sensors. [ABSTRACT FROM AUTHOR]

Lead zirconate titanate (PZT)-based piezoelectric ceramics are important functional materials for various electromechanical applications due to their excellent performance and temperature stability. Herein, the rhombohedral PbZr 0.55 Ti 0.45 O 3 ceramics with increasing average grain size from 3.57 μm to 10.85 μm were prepared by a conventional solid-state reaction method. The grain-size dependent dielectric, ferroelectric and piezoelectric properties were systematically investigated. With the increasing grain size, a significant softening effect with enhanced electromechanical properties was observed. Results of piezoresponse force microscopy show that the formation of non-180° domain walls was strongly repressed in the fine-grain samples, resulting in decreased domain wall mobility. Meanwhile, a noteworthy hardening effect was also observed in the coarse-grain samples with high domain wall mobility, which may be related to the enhanced bulk effect with increasing grain size. The results of this work confirmed that grain size engineering is an effective strategy for designing piezoelectric materials with excellent combination properties. [ABSTRACT FROM AUTHOR]

High‐performance piezoelectric materials are essential in many piezoelectric devices. However, the composition of piezoelectric materials usually has a great influence on their performance. In this work, xBi(Mg1/2Ti1/2)O3–yPbZrO3–zPbTiO3 (xBMT–yPZ–zPT; 0.2 ≤ x ≤ 0.4, 0.25 ≤ y ≤ 0.4, and 0.35 ≤ z ≤ 0.4) ternary ceramics with different compositions were synthesized and it was found that the strain response was not sensitive to the composition. The crystal structure, strain response, ferroelectric properties, and temperature stability of xBMT–yPZ–zPT ceramics were investigated in detail. X‐ray diffraction patterns show that all the as‐prepared xBMT–yPZ–zPT ceramics with x = 0.2, 0.3, 0.4, and 0.5 possess a perovskite structure. Under an external electric field of 6 kV mm−1, the strain values of xBMT–yPZ–zPT ternary ceramics with x = 0.2, 0.3, 0.4, and 0.5 were 0.30%, 0.31%, 0.30%, and 0.27%, respectively. In addition, the strain hysteresis of these ternary ceramics is also almost the same and low. These merits make xBMT–yPZ–zPT piezoelectric ceramics have broad application prospects in the field of commercial actuators. [ABSTRACT FROM AUTHOR]

In this paper, (1- x)CaBi 2 Nb 2 O 9 - x Na 0.5 Bi 2.5 Nb 2 O 9 [(1- x)CBN- x NBN; x = 0, 0.1, 0.3, 0.5 and 0.7] ceramics were prepared by the traditional solid-state method. The structure and properties of CBN and NBN are very close to each other, and XRD shows that Na/Bi ions have entered the lattice of CBN. By adjusting the content of NBN in (1- x)CBN- x NBN ceramics, the crystal structure of the ceramics undergoes a pseudo-tetragonal distortion that can significantly improve thermal stability. Analysis of the data of XRD refinement confirms there is pseudo-tetragonal phase at x = 0.1 to 0.5. Moreover, the remnant polarization P r is obviously improved due to the reduction of grain size and pseudo-tetragonal distortion. Although the Curie temperature of the CBN-NBN piezoelectric ceramics decreases, the tan δ at high temperatures is significantly reduced and the DC resistivity is increased. The 0.5CBN-0.5NBN ceramic shows excellent comprehensive properties: d 33 of 13.8 pC/N, T c of 873 °C, tan δ of 2.1% at 500 °C, and P r of 8.92 μC/cm2, especially the d 33 maintains 94.9% of the initial d 33 after depolarization at 850 °C, which has competitiveness in the high-temperature piezoelectric materials. [ABSTRACT FROM AUTHOR]

Bismuth sodium titanate (BNT)-based, lead-free piezoelectric materials have been extensively studied due to their excellent strain characteristics and environmental friendliness. In BNTs, the large strain (S) usually requires a relatively large electric field (E) excitation, resulting in a low inverse piezoelectric coefficient d33* (S/E). Moreover, the hysteresis and fatigue of strain in these materials have also been bottlenecks impeding the applications. The current common regulation method is chemical modification, which mainly focuses on forming a solid solution near the morphotropic phase boundary (MPB) by adjusting the phase transition temperature of the materials, such as BNT-BaTiO3, BNT-Bi0.5K0.5TiO3, etc., to obtain a large strain. Additionally, the strain regulation based on the defects introduced by the acceptor, donor, or equivalent dopant or the nonstoichiometry has proven effective, but its underlying mechanism is still ambiguous. In this paper, we review the generation of strain and then discuss it from the domain, volume, and boundary effect perspectives to understand the defect dipole behavior. The asymmetric effect caused by the coupling between defect dipole polarization and ferroelectric spontaneous polarization is expounded. Moreover, the defect effect on the conductive and fatigue properties of BNT-based solid solutions is described, which will affect the strain characteristics. The optimization approach is appropriately evaluated while there are still challenges in the full understanding of the defect dipoles and their strain output, in which further efforts are needed to achieve new breakthroughs in atomic-level insight. [ABSTRACT FROM AUTHOR]

Piezoelectric textured ceramics have drawn increasing research and industry interests by balancing the production cost and material performances. A new approach to realize the texture in piezoelectric ceramics is developed based on 3D printing stereolithography (SL) technique and successfully applied in the preparation of < 001 > -textured 0.71(Sm 0.01 Pb 0.985)(Mg 1/3 Nb 2/3)O 3 -0.29(Sm 0.01 Pb 0.985)TiO 3 (1 %Sm-PMN-29PT) ceramics in this work. As a critical process in texture ceramic fabrication, the alignment of BaTiO 3 templates along the horizontal direction is achieved by the shear force produced from the relative motion between the resin container and the blade during SL. The textured ceramics with obvious grain orientation features are successfully obtained. The enhanced piezoelectric properties of d 33 ≈ 652 pC N−1 and d 33 * ≈ 800 pm V−1 are achieved in the 3D printed textured ceramic, which are about 60 % and 40 %, respectively, higher than their non-textured counterparts. Moreover, the textured sample shows a significant improvement on thermal stability of d 33 * T , which varies by less than ± 6 % from RT to 110 °C. Furthermore, the introduction of 3D printing into the synthesis of textured piezoelectric ceramics shows great advantages over the traditional tape-casting method. This work is expected to provide a promising way for the future design of textured piezoelectric functional materials. [ABSTRACT FROM AUTHOR]

Bi 0.5 Na 0.5 TiO 3 (BNT)-based complexes, one of the most promising piezoelectric materials, have been recently raised as potential ionic conductors. Although the property modification of BNT-based materials was studied intensively, the influence of the preparation process on the structure and conduction mechanism has not received the attention it deserves since its particular sensitivity to the conductive performance. Herein, (Bi 0.44 Nd 0.01 Sr 0.02 Ca 0.02)Na 0.5 TiO 2.965 (BNSCNT) ceramics were prepared by tape-casting (TC) and conventional solid-state reaction (SR) method, respectively. Despite the pure perovskite phase with rhombohedral distortion of BNSCNT ceramics prepared by SR, the rutile titanium dioxide phase can be identified for TC. The ac impedance spectra reveal a discernible bulk response with appreciable oxide ion conductive capacity in SR, while the contribution from each physical origin becomes obscure due to the superposition in the Nyquist plots of TC. Combined with the activation energy deduced from the thermally dependent conductivity, which is significantly less than the dielectric BNTs, the dominated ionic conductive nature with non-negligible electron contribution is proposed. The grain boundary and electrodes/interfaces response, and their conduction mechanism in the intermediate frequencies range are disclosed by employing the dc bias field and atmospheres. The field-induced inverse variation is recognized of which the dissociation of defect clusters is responsible for SR, whereas the trapping of conduction electrons on the sample surface and the second phase will play the key role for TC, in determining their impedance. This work raises the great importance of the preparation route on the structure and conduction mechanisms of BNT-based oxide ionic conductive materials. [ABSTRACT FROM AUTHOR]

Long-time electric field action on perovskite piezoelectric ceramic leads to chemical degradation. A new way to accelerate the degradation is the exposure of the ceramic to DC electric fields under a vacuum. A high-quality commercial piezoelectric material based on PbZr1−xTixO3 is used to study such impacts. To avoid the influence of ferroelectric properties and possible removal of oxygen and lead oxides during the degradation process, the experiments are in the temperature interval of 500 °C > T > TC. Changes in resistance during the electrodegradation process is an electrically-induced deoxidation, transforming the ceramic into a metallic-like material. This occurs with an extremely low concentration of effused oxygen of 1016 oxygen atoms per 1 cm3. Due to this concentration not obeying the Mott criterion for an isolator-metal transition, it is stated that the removal of oxygen mostly occurs along the grain boundaries. It agrees with the first-principle calculations regarding dislocations with oxygen vacancies. The decrease in resistivity during electrodegradation follows a power law and is associated with a decrease in the dislocation dimension. The observed reoxidation process is a lifeline for the reconstructing (self-healing) properties of electro-degraded ceramics in harsh cosmic conditions. Based on all of these investigations, a macroscopic and nanoscopic model of the electrodegradation is presented. [ABSTRACT FROM AUTHOR]

The (K,Na)NbO 3 -based ceramics are a very promising type of lead-free piezoelectric materials. In spite of the scientific and technological importance, systematical investigations on the dielectric spectra had been rarely performed so far. This paper reports our study results obtained in the (K 0.50 Na 0.50) 1- x Li x NbO 3 ceramics with either x = 0.03 or x = 0.065 (denoted as KNLN-030 and KNLN-065 ceramics, respectively) in the unpoled state and the poled state, respectively. Before poling, the KNLN-030 ceramic shows a dielectric spectrum of strong frequency dependence with a broad peak of dielectric loss around 1 MHz, while the KNLN-065 one has a dielectric spectrum of weak frequency dependence below 60 MHz at room temperature. After poling, piezoelectric resonance peaks appear and are accompanied by a large step-like reduction of dielectric permittivity ε′ in the dielectric spectra of both two ceramics. More interestingly, the KNLN-065 ceramic exhibits an abnormal phenomenon that there is a marked increases in low-frequency ε′ upon poling, whereas the KNLN-030 one shows normally a large decrease of low-frequency ε′. Further, the KNLN-065 ceramic displays the larger low-frequency ε′ in the poled state than in the unpoled state over a considerably wide temperature range. By contrast, such abnormal phenomenon is recognized only in a limited region above the orthorhombic-tetragonal phase transition in the KNLN-030 ceramic. The analysis of domain structure suggests that the observed abnormal dielectric phenomenon possibly arises from the enhancement of domain-wall mobility. [ABSTRACT FROM AUTHOR]

One of the crucial issues in developing lead-free piezoelectric materials for actuator applications lies in how to achieve large strain responses. Herein, a strategy that strengthens the synergistic contribution of reversible phase transition and ferroelectric domain switching via modulating the ferroelectric-to-relaxor transition temperature (TF−R) was proposed to improve the strain level. Following this strategy, an enhanced strain response was attained by introducing Bi(Zn2/3Ta1/3)O3 (BZT) into Bi0.5(Na0.8K0.2)0.5TiO3 (BNKT) matrix. The enhanced bipolar strain (Sbi) of 0.50% and the unipolar strain (Suni) of 0.56% were obtained in BNKT-0.025BZT ceramic, respectively, with corresponding normalized strain d33* values of 833 and 933 pm/V (@60 kV/cm). Besides, BNKT-0.05BZT ceramic exhibited excellent energy storage behavior with a recoverable energy storage density Wrec of 1.05 J/cm3 at 90 kV/cm. These findings demonstrate that BNKT-xBZT ceramics are promising material candidates for actuators and energy storage applications. [ABSTRACT FROM AUTHOR]

Multilayer ceramic actuators with a base metal internal electrode are in great demand because of their high voltage-driven displacement. Thus, the piezoelectric materials should be sintered in low oxygen partial pressure. The (Li, Ta, Sb)-doped (K,Na)NbO3 (KNN)-based ceramics are heat-treated in O2, air, N2, and 99 vol. % N2/1 vol. % H2 mixture gas at 300 °C in this study to identify the predominant charge carriers by defect chemistry. By analyzing electrical conduction and dielectric relaxation mechanisms, the dominant charge carriers in the ceramics are electrons and oxygen vacancies at low (<450 °C) and high temperature (>500 °C), respectively. In addition, the defect concentration in the ceramics increases with the decreasing oxygen partial pressures, and the change is more evident in the presence of H2 gas. Correspondingly, the electrical properties slightly degrade with the decreasing oxygen partial pressure and severely degrade in the N2/H2 mixture gas. Therefore, the (Li, Ta, Sb)-doped KNN-based ceramics with an n-type conduction mechanism are difficult to sinter in a reducing atmosphere. In order to cofire with base metal electrodes, the p-type conduction should be designed by doping the KNN ceramic in the future for industrial application. [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]

Bi0.5Na0.5TiO3 (abbreviated as BNT)-based ceramics are considered the promising candidates for lead-free piezoelectric materials to replace the widely used lead zirconate titanate (PZT)-based piezoelectric ceramics. Piezoelectric properties could be modulated by porous structures to meet the needs of piezoelectric energy converters. Porous (Bi0.5Na0.5)0.94Ba0.06TiO3 (BNT-6BT) ceramics had been prepared by using kiwi pollen as a sacrificial template for inducing U-shaped micropores. Porosity correlations of dielectric and piezoelectric properties of the porous BNT-6BT ceramics in the relative porosity range of 0–50% were obtained and analyzed. The temperature stability of the dielectric constant of porous ceramics is significantly improved, while the dielectric constant of porous ceramics decreases rapidly with the increase of the amount of pollen added, and then remains stable. The longitudinal piezoelectric coefficient d33 and the transverse piezoelectric coefficient d31 of porous ceramics decrease slowly with porosity. It was found that the ceramic barrier hinders the pinning effect of the micro stress and strain on domain walls, which makes the piezoelectric properties of porous ceramics well maintained. Porous BNT-based ceramics have great application value in underwater acoustic transducers and other fields. [ABSTRACT FROM AUTHOR]

In this study, lead-free 0.8(Bi,Na)TiO3-0.2(Sr,Ti)O3 piezoelectric ceramics were prepared using a two-step sintering process to analyze their sintering mechanisms. Two-step sintering process has benefits of being able to be conducted at lower temperatures than conventional sintering process, but the complicated sintering mechanisms involved in this process have not been yet fully investigated. Therefore, in the present study, two-step sintering mechanism for lead-free piezoelectric ceramics was analyzed by estimating the activation energy required depending on the sintering conditions. Using the two-step sintering process, the piezoelectric charge and electromechanical coupling coefficients improved from 146 pC/N and 0.347 to 163 pC/N and 0.377, respectively. By comparing the grain-growth mechanisms for the conventional and two-step sintering processes, it appeared that the sintering mechanisms differed. By introducing the two-step sintering process, piezoelectric ceramics with improved piezoelectric charge and electromechanical coupling coefficients were produced. [ABSTRACT FROM AUTHOR]

In this study, the composition of lead-free piezoelectric ceramics (1 − x)(Bi0.5Na0.5)TiO3–x(Ba0.5Sr0.5)TiO3 with excellent piezoelectric properties was investigated. Crystal analysis and electrical and piezoelectric properties were analyzed according to the content of the BST composition. A phase change from rhombohedral to tetragonal structure was observed in 0.12 BST, and the densest and most uniform microstructure was confirmed in this composition. The dielectric constant increased from 905 to 1692 as the composition of BST increased to 0.12 BST. Afterward, as the composition of BST increased, the permittivity tended to decrease. Additionally, at 0.12 BST, Pr was the highest at 23.34 μC/cm2. The piezoelectric charge constant (d33) and the electromechanical coupling coefficient (kp) were 152 pC/N and 0.37, respectively, and showed the highest values at 0.12 BST. Curie temperature (Tm) was analyzed 242 °C at 0.12 BST, the optimal composition. It was confirmed that the characteristics of 0.12 BST were excellent in all conditions. Therefore, it was confirmed that 0.12 BST is the optimal composition for (1 − x)BNT–xBST piezoelectric ceramics. [ABSTRACT FROM AUTHOR]

Ferroelectric ceramics have good piezoelectric and ferroelectric properties and can be used for energy storage equipment and actuators. Nevertheless, current research on dielectric capacitors has only focused on the energy storage density, but ignored efficiency. Moreover, conventional piezoelectric materials have a large strain hysteresis. In this work, (Al 0.5 Nb 0.5)4+ (AN) complex ions doped 0.7Bi 0.5 Na 0.5 TiO 3 -0.3Ba 0.3 Sr 0.7 TiO 3 (BNBST) ceramics were prepared. Doping AN destroyed the long-range ordered ferroelectric domains and generated polar nano regions, resulting in a gradual thinning and inclination of polarization hysteresis loops and an increase in relaxor degree. For BNBST-3AN ceramics, a W rec of 1.52 J/cm3 and a η of 92.1% were achieved at 150 kV/cm. Meanwhile, BNBST-3AN ceramics had good energy storage temperature stability and cycling performance. The AN doping reduced the strain hysteresis in BNBST ceramics. BNBST-2AN ceramics exhibited a longitudinal electrostrictive coefficient Q 33 ∼ 0.0292 m4/C2 and a field-induced strain of 0.25% with low strain hysteresis (6.67%). Furthermore, BNBST-4AN ceramics had superior dielectric temperature stability from 24 to 270 °C. All results show that BNBST-100 x AN ceramics have great promise for energy storage devices and actuators. [ABSTRACT FROM AUTHOR]

This work was devoted to the first multi-parametric unitary comparative analysis of a selection of sintered piezoceramic materials synthesised by solid-state reactions, aiming to delineate the most promising biocompatible piezoelectric material, to be further implemented into macro-porous ceramic scaffolds fabricated by 3D printing technologies. The piezoceramics under scrutiny were: KNbO3, LiNbO3, LiTaO3, BaTiO3, Zr-doped BaTiO3, and the (Ba0.85Ca0.15)(Ti0.9Zr0.1)O3 solid solution (BCTZ). The XRD analysis revealed the high crystallinity of all sintered ceramics, while the best densification was achieved for the BaTiO3-based materials via conventional sintering. Conjunctively, BCTZ yielded the best combination of functional properties—piezoelectric response (in terms of longitudinal piezoelectric constant and planar electromechanical coupling factor) and mechanical and in vitro osteoblast cell compatibility. The selected piezoceramic was further used as a base material for the robocasting fabrication of 3D macro-porous scaffolds (porosity of ~50%), which yielded a promising compressive strength of ~20 MPa (higher than that of trabecular bone), excellent cell colonization capability, and noteworthy cytocompatibility in osteoblast cell cultures, analogous to the biological control. Thereby, good prospects for the possible development of a new generation of synthetic bone graft substitutes endowed with the piezoelectric effect as a stimulus for the enhancement of osteogenic capacity were settled. [ABSTRACT FROM AUTHOR]

Solid solutions of BiFeO 3 and BaTiO 3 are promising lead-free piezoelectric materials, especially around the morphotropic phase boundary at 0.67BiFeO 3 -0.33BaTiO 3. Still, these materials are challenged by phase instability and limited understanding of the processing-properties relationship. Here, we investigate mechanochemical activation and the use of BaTiO 3 as seed particles for the 0.67BiFeO 3 -0.33BaTiO 3 phase. Contrary to expectations from seeding in lead-based perovskites, the BaTiO 3 seeds do not promote the 0.67BiFeO 3 -0.33BaTiO 3 perovskite phase neither during the mechanochemical activation nor the subsequent sintering, but cause an inhomogeneous structure with remnant BaTiO 3. This results in ceramics with weaker low-field piezoelectric response than that of the unseeded route, but with higher field-induced strain, even up to 150 °C. Both routes produce ceramics of high density and without significant secondary phases visible by X-ray diffraction. This demonstrates the advantage of mechanochemical activation and the possibility to tailor the piezoelectric response of 0.67BiFeO 3 -0.33BaTiO 3 through the processing route. [ABSTRACT FROM AUTHOR]

Flexible energy harvesters have become a research hotspot in both academia and industry because of their great advantages in powering wearable electronic devices. The flexible energy harvesters based on piezoelectric materials are recognized as a competitive method because of their sensitivity to mechanical deformation, excellent energy conversion performance, mature production technology, and simple structure. This paper presents a comprehensive review to illustrate the research progress and future development of wearable flexible piezoelectric harvesters. In this work, the widely used piezoelectric materials for flexible energy harvesters, including inorganic piezoelectric materials, organic piezoelectric materials, and piezoelectric composites, are first summarized. The research progress on the influence of ceramic content, morphology, distribution, surface chemical modification, and the addition of conductive materials on the properties of piezoelectric composites are systematically discussed. Additionally, this paper also presents novel structures and fabrication methods of flexible piezoelectric energy harvesters. Finally, future trends in research, development, and innovation of flexible piezoelectric energy harvesters are outlined and prospected. [ABSTRACT FROM AUTHOR]

Lead-free ceramics are promising candidates for replacing lead-based piezoelectric materials such as lead-zirconate-titanate (PZT) if they can compete in dielectric and ferroelectric characteristics. In this work, for lead-free piezoelectric ceramic, 0.74(Bi0.5Na0.5TiO3)-0.26(SrTiO3) (BNT-ST26) and niobium-substituted (Nb-BNT–ST26) ceramics were synthesized by solid-state reactions. The evolution of niobium substitution to the perovskite phase structure of BNT-ST26 ceramics was confirmed by X-ray diffraction (XRD) analysis and Raman spectra. Electromechanical properties of Nb-BNT-ST26 ceramics initially increased with the addition of niobium up to 0.5% and decreased with a further increase in Nb content. Temperature-dependent dielectric curves showed that the depolarization temperature (Td) decreased below room temperature because of Nb substitution. The composition with 0.5% Nb yielded a maximum bipolar strain (Smax) of 0.265% and normalized strain of d33* ~ 576 pm/V under an electric field of 4.6 kV/mm at room temperature. At this critical concentration of 0.5% Nb, maximum saturation polarization of 26 μC/cm2 was achieved. The dielectric constant with temperature peaks became more diffused and the depolarization temperature decreased with the increasing Nb content. The study concludes that Nb-doped BNT-ST26 is an excellent material for high-temperature, stable, frequency-dependent, lead-free piezoelectric devices. [ABSTRACT FROM AUTHOR]