Large Piezoelectric Coefficient D33 Research Articles

Structure distortion enhanced electrical performances of Na0.25K0.25Bi2.5Nb2O9-based high-temperature piezoceramics

Na0.25K0.25Bi2.5Nb2O9-based piezoelectric ceramics are potential candidates for high-temperature applications where improving piezoelectric properties is an urgent issue. In this work, significantly improved piezoelectric properties and thermal stability of Na0.25K0.25Bi2.5-xCexNb2-yWyO9 (abbreviated NKB2.5-xCxN2-yWy, x = 0.03, y = 0.01, y = 0.03, y = 0.05) ceramics were obtained through Ce and W co-doping and using a traditional solid-state technique. The optimal composition of NaKBi2.47Ce0.03Nb1.99W0.01O9 exhibits a large piezoelectric coefficient d33 of 23.1 pC/N, maintains a high Curie temperature Tc of 690 °C, and a low tanδ of 0.006. The increase of d33 may be attributed to the structure distortion, the micro-sized domains, and the high-density domain walls. More importantly, its d33 value maintains 86 % of the initial value after being annealed at 650 °C for 2 h, whereas only 65 % for the undoped sample under the same conditions, indicating an obviously improved thermal stability. This work provides a new idea for improving piezoelectric properties and thermal stability of Na0.25K0.25Bi2.5Nb2O9-based piezoelectric ceramics.

Fabrication of BiScO3–PbTiO3/epoxy 1–3 piezoelectric composites for high‐temperature transducer applications

Abstract1–3 piezoelectric composites are widely used in piezoelectric ultrasonic transducers due to their high thickness electromechanical coupling factor. However, the applications of the composites in high‐temperature fields are limited by the low heat resistance of both the piezoelectric and polymer phases. To tackle this, we designed and fabricated the BiScO3–PbTiO3/epoxy high‐temperature 1–3 piezoelectric composites. These composites exhibit a high thickness electromechanical coupling factor kt of 63%, a large piezoelectric coefficient d33 of 470 pC/N, and a pure thickness vibration mode. Furthermore, we fabricated a high‐temperature transducer based on the BiScO3–PbTiO3/epoxy 1–3 composites. The bandwidths of the composites measured in water and silicone oil (30% and 23%, respectively) are approximately 1.65 times greater than those of monolithic piezoelectric ceramics (18% and 14%, respectively). The bandwidth of the transducer can be increased to 78% by adding a porous alumina backing layer, with the working temperature reaching up to 300°C. The results indicate that the BS–PT/epoxy 1–3 composite is a potential candidate for high‐temperature transducer applications.

Multiscale Structural Engineering Boosts Piezoelectricity in Na0.5Bi2.5Nb2O9-Based High-Temperature Piezoceramics.

High-temperature piezoelectric materials, which enable the accurate and reliable sensing of physical parameters to guarantee the functional operation of various systems under harsh conditions, are highly demanded. To this end, both large piezoelectricity and high Curie temperature are pivotal figures of merit (FOMs) for high-temperature piezoceramics. Unfortunately, despite intensive pursuits, it remains a formidable challenge to unravel the inverse correlation between these FOMs. Herein, a conceptual material paradigm of multiscale structural engineering was proposed to address this dilemma. The synergistic effects of phase structure reminiscent of a polymorphic phase boundary and refined domain morphology simultaneously contribute to a large piezoelectric coefficient d33 of 30.3 pC/N and a high Curie temperature TC of 740 °C in (LiCeNd) codoped Na0.5Bi2.5Nb2O9 (NBN-LCN) ceramics. More encouragingly, the system has exceptional thermal stability and is nonsusceptible to mechanical loading. This study not only demonstrates that the high-performance and robust NBN-LCN high-temperature piezoceramics hold great potential for implements under harsh conditions but also opens an avenue for integrating antagonistic properties for the enhancement of the collective performance in functional materials.

Biodegradable ferroelectric molecular crystal with large piezoelectric response.

Transient implantable piezoelectric materials are desirable for biosensing, drug delivery, tissue regeneration, and antimicrobial and tumor therapy. For use in the human body, they must show flexibility, biocompatibility, and biodegradability. These requirements are challenging for conventional inorganic piezoelectric oxides and piezoelectric polymers. We discovered high piezoelectricity in a molecular crystal HOCH2(CF2)3CH2OH [2,2,3,3,4,4-hexafluoropentane-1,5-diol (HFPD)] with a large piezoelectric coefficient d33 of ~138 picocoulombs per newton and piezoelectric voltage constant g33 of ~2450 × 10-3 volt-meters per newton under no poling conditions, which also exhibits good biocompatibility toward biological cells and desirable biodegradation and biosafety in physiological environments. HFPD can be composite with polyvinyl alcohol to form flexible piezoelectric films with a d33 of 34.3 picocoulombs per newton. Our material demonstrates the ability for molecular crystals to have attractive piezoelectric properties and should be of interest for applications in transient implantable electromechanical devices.

H/F substitution achieves high piezoelectricity in enantiomeric molecular crystals.

Here, we successfully synthesized a pair of enantiomeric molecular piezoelectric materials by H/F substitution strategy. These compounds show a large piezoelectric coefficient d33 value of 25 pC N-1 measured by the quasi-static method. A simple energy harvesting device was fabricated based on this crystal, showing great potential in piezoelectric mechanical energy harvesters.

Conformally Large-Area Single-Crystal Piezocomposites with High Performance for Acoustic Transducers.

Large-area and conformal piezoelectric elements are highly desired for acoustic transducers to possess a large power source level and wide detecting range. To date, single-crystal piezocomposites attract much attention on enhancing the power source level and bandwidth for next-generation acoustic transducers, owing to their higher piezoelectric and electromechanical coupling properties compared to traditional piezocomposites. Unfortunately, it is still challenging to achieve large-area and conformal single-crystal piezocomposites because of the fragile nature, large anisotropy, and the limited grown size of piezoelectric single crystals. Here, we successfully fabricate the conformally large-area single-crystal piezocomposite with an area of 160 × 50 mm2 and a bending angle of 162° by a modified 3D-printing-assisted inserting method. The single-crystal piezocomposite exhibits a high thickness electromechanical coupling factor kt of 85% and a large piezoelectric coefficient d33 of 1150 pC/N, surpassing those of the reported large-area piezocomposites. The influence of the volume fraction and curvature radius of single-crystal PCs and acoustic transducers was investigated. Furthermore, we designed an acoustic transducer based on the conformal single-crystal piezocomposite. Benefiting from the excellent piezoelectric and electromechanical properties of the single-crystal piezocomposite, the transducer indicates a high maximum transmitting voltage response of 171.8 dB. Especially, its bandwidth (-3 dB) achieves 60 kHz with a resonant frequency of 292 kHz, which is about 1.8 times superior to the conformal acoustic transducer based on the ceramic piezocomposite with a similar resonant frequency. This work may benefit the future design and fabrication of high-performance and complex-shape piezoelectric composites as key materials for next-generation transducers.

The First Ring Enlargement Induced Large Piezoelectric Response in a Polycrystalline Molecular Ferroelectric.

Inorganic ferroelectrics have long dominated research and applications, taking advantage of high piezoelectric performance in bulk polycrystalline ceramic forms. Molecular ferroelectrics have attracted growing interest because of their environmental friendliness, easy processing, lightweight, and good biocompatibility, while realizing the considerable piezoelectricity in their bulk polycrystalline forms remains a great challenge. Herein, for the first time, through ring enlargement, a molecular ferroelectric 1-azabicyclo[3.2.1]octonium perrhenate ([3.2.1-abco]ReO4 ) with a large piezoelectric coefficient d33 up to 118 pC/N in the polycrystalline pellet form is designed, which is higher than that of the parent 1-azabicyclo[2.2.1]heptanium perrhenate ([2.2.1-abch]ReO4 , 90 pC/N) and those of most molecular ferroelectrics in polycrystalline or even single crystal forms. The ring enlargement reduces the molecular strain for easier molecular deformation, which contributes to the higher piezoelectric response in [3.2.1-abco]ReO4 . This work opens up a new avenue for exploring high piezoelectric polycrystalline molecular ferroelectrics with great potential in piezoelectric applications.

Outstanding electromechanical performance in piezoelectric ceramics via synergistic effects of defect engineering and domain miniaturization

Piezoelectric ceramics with high mechanical quality factor Qm and large piezoelectric coefficient d33 are urgently required for advanced piezoelectric applications. However, obtaining both of these properties simultaneously remains a difficult challenge due to their mutually restrictive relationship. Here 0.5Pb(Ni1/3Nb2/3)O3–0.5Pb(Zr0.3Ti0.7)O3 piezoceramic with tetragonal (T)-rich MPB is designed as a matrix to construct the defect engineering by doping low-valent Mn ions. The strong coupling of defect dipole and T-rich phase can effectively hinder the rotation of Ps, restrict domain wall motion and improve Qm. At the same time, the substituted Mn ions will introduce local random field, destroying the long-range ordering of ferroelectric domain and reducing domain size. The miniaturized domain structure can increase poling efficiency and inhibit the reduction of d33. Guided by this strategy, Qm has increased by more than 10 times and d33 has only decreased by about 25%. The optimized electromechanical performance with Qm = 822, d33 = 502 pC/N, kp = 0.55 and tanδ = 0.0069 can be obtained in the present study.

Inch-Size Molecular Ferroelectric Crystal with a Large Electromechanical Coupling Factor on Par with Barium Titanate.

Molecular ferroelectrics with large piezoelectric responses have long been sought for their advantages of light weight, mechanical flexibility, and easy preparation, in contrast to the widely used inorganic counterparts. Representatively, a molecular ferroelectric crystal [Me3NCH2Cl]CdCl3 (TMCM-CdCl3) has been found to show a large piezoelectric coefficient d33 of 220 pC/N exceeding that of BaTiO3 (You et al. Science2017, 357, 306-309). However, although the d33 of molecular ferroelectrics has achieved great progress, their electromechanical coupling factor k33, which is essential for various piezoelectric applications, including ultrasonic transducers and actuators, was rarely explored and is far below the level of inorganic ferroelectrics. The major reason for this situation is the great challenge of growing large-size crystals which is a key limiting factor for measuring k33. Here, we grew inch-size crystals of organic-inorganic perovskite ferroelectric TMCM-CdCl3 with a high d33 (383 pC/N) for investigating its piezoelectric responses including the k33 (0.483) by the resonance method. Such high k33 (0.483) is much larger than those of other molecular ferroelectrics and competitive with that of BaTiO3 (0.5). In addition, TMCM-CdCl3 has a low elastic modulus of 13.03 GPa, an order of magnitude lower than that of BaTiO3. This finding sheds light on the exploration of large electromechanical coupling factors in molecular ferroelectrics for potential applications in flexible and portable piezoelectric devices.

High-Performance Curved Piezoelectric Single-Crystal Composites via 3D-Printing-Assisted Dice and Insert Technology for Underwater Acoustic Transducer Applications.

Piezoelectric single-crystal composites (PSCCs) have been studied and applied because of their improved resolution and power source level performance in underwater acoustic transducer applications relative to traditional piezoelectric ceramic composites (PCCs). Currently, the methods to fabricate curved PSCCs are mostly derived from PCCs, including molding with flexible backing, molding with heating, and molding with the casting rubber method. Unfortunately, the methods mentioned above are not suitable for preparing curved PSCCs for underwater acoustic transducer applications because of their brittleness, the large anisotropy of piezoelectric single crystals, and the high thickness (>2 mm) of PSCCs for achieving the low operating frequency (<700 kHz). In the present work, we proposed a preparation method, 3D-printing-assisted dice and insert technology, and successfully prepared curved PSCCs with high performance. Although the PSCCs have a low volume fraction of single crystals in this work (∼33%), a high thickness electromechanical factor kt of 86% and a large piezoelectric coefficient d33 of 1550 pC/N were achieved in the curved 1-3 PSCCs, which are superior to other reported PSCCs and PCCs with nearly the same volume fraction of single crystals and piezoelectric ceramics. This work presents a paradigm for fabricating curved PSCCs for underwater acoustic transducers, and this method shows the potential for large-area, special-shaped PSCCs, which are key materials for next-generation underwater acoustic transducers.

Study of domain configurations in (Bi,Na)ZrO3-modified (K,Na)(Nb,Sb)O3 piezoelectric ceramics by acid-etching at different temperatures

Domain structure often greatly affects piezoelectric performance of a ferroelectric ceramic. Accordingly, a convenient method that can well characterize the domain structure at various temperatures is highly desired for understanding the underlying mechanism. An improved acid-etching technique was recently developed for such purpose. Domain structure of poled 0.96(K0.48Na0.52)(Nb0.96Sb0.04)O3–0.04(Bi0.50Na0.50)ZrO3 ceramics with a large piezoelectric coefficient d33 of 535 pC/N was systematically investigated at three typical temperatures. It was found that domain configurations change significantly with temperature. Hierarchical nanodomain structure is widely observed in domain patterns acid-etched at 25 °C, due to the orthorhombic-tetragonal phase coexistence. By contrast, the majority part of those acid-etched at − 60 °C are simply some long parallel stripes, while a small amount of banded structure appears in broad stripes inside some grains. A nearly 63° intersectional angle is seen between two adjacent sets of parallel stripes in the domain pattern of a cuboid-shaped grain, indicating that orthorhombic phase remains down to − 60 °C. The domain patterns acid-etched at 80 °C become even simpler, mainly consisting of long parallel stripes that are several hundred nanometers wide and have quite straight edges. Fundamental issues associating with the possible domain configurations and the acid-etching were discussed on the simple mathematical basis.

Unexpectedly high piezoelectric response in Sm-doped PZT ceramics beyond the morphotropic phase boundary region

Abstract Compositional design by multiphase coexistence is regarded as a guiding rule for material design to develop high-performance piezoelectric materials. An open question is whether a certain PZT composition outside of the morphotropic phase boundary (MPB) region can obtain high piezoelectric response like that close to MPB region. Here, a non-MPB composition, rhombohedral Pb(Zr0.54Ti0.46)O3 was selected as the parent material. The optimized electrical properties were obtained by Sm doping with a large piezoelectric coefficient d33 of 590 pC/N, a high planar electromechanical coupling factors kp of 57.1%, a large piezoelectric strain S of 0.31% (d33∗ = 632 pm/V), and a promising Curie temperature of 335 °C, compared to the commercial PZTs. The enhancement of piezoelectric response can be ascribed to the donor characteristics by Sm replacement, which contribute to polarization orientation of ferroelectric dipoles. This work broadens the domain of high-performance piezoelectrics by developing novel solid solutions beyond the MPB framework.

Enhanced temperature stability and tailored electromechanical response in (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 piezoceramics through rare earth modification

(Ba,Ca)(Zr,Ti)O3 piezoceramics are deemed as one of potential lead-free alternatives to commonly used lead-based piezoelectric ceramics because of their high piezoelectric properties. However, in the process of improving their electrical properties, it tends to cause significant deterioration of thermal, frequency, and fatigue stability for electromechanical response, which will impede the commercialization of piezoelectric materials. Herein, we designed a strategy using the rare earth to modify BCZT lead-free piezoceramics so as to solve the above mentioned challenges. In this work, for Ho-modified BCZT lead-free ceramics, we achieved not only high electromechanical response with Smax/Emax = 550 pm/V and large piezoelectric coefficient d33 = 521 pC/N, but also the enhanced temperature stability featured by < 2% variation for d33 in the general operating temperature range of 20 °C and 70 °C. In addition, large electrostrictive coefficient Q33 of 0.045 m4/C2 was also realized in this modified materials while still maintaining good temperature stability. More interestingly, this modified materials also performed excellent fatigue endurance, evidenced by < 3% variation for the remnant polarization (Pr) and Smax/Emax after 105 cycles. The complex impedance spectra verified that the boosted fatigue resistance was mainly attributed to the decrease of the defect density originating from the reduced oxygen vacancies. These results demonstrate that the introduction of rare earth into BCZT is an effective way to tailor temperature stability and electromechanical responses.

The Search for BaTiO3-Based Piezoelectrics With Large Piezoelectric Coefficient Using Machine Learning.

We employ a data-driven approach to search for BaTiO3-based piezoelectrics with large piezoelectric coefficient d33. Our approach uses a surrogate model to make predictions of d33 with uncertainties, followed by a design step that selects the next optimal compound to synthesize. We compare several combinations of choices of the model and design selection strategies on the training data assembled from many experiments that we have previously performed, and we choose the best two performers for guiding new experiments. This adaptive design strategy is iterated five times and in each iteration, four new compounds are synthesized based on the two different design selection criteria. The best new compound found in this work is (Ba0.85Ca0.15)(Ti0.91Zr0.09)O3 with a d33 of 362 pC/N, compared to the best compound BCT-0.5BZT in the training data with a d33 of ~610 pC/N. Our conclusion from this study is that although our model describes well most of the available d33 data, the especially large value for BCT-0.5BZT is difficult to fit with any surrogate model and emphasizes the need to combine a physics-based approach with a pure data-driven approach used in this study.

Outstanding piezoelectric properties, phase transitions and domain configurations of 0.963(K0.48Na0.52)(Nb0.955Sb0.045)O3−0.037(Bi0.50Na0.50)HfO3 ceramics

Requirements for substituting the current lead-based piezoelectric materials with lead-free ones are becoming increasingly strong from environmental concerns. In this article, we report piezoelectric properties, phase transitions and domain configurations of a dense 0.963(K0.48Na0.52)(Nb0.955Sb0.045)O3−0.037(Bi0.50Na0.50)HfO3 lead-free ceramic prepared through solid-state reaction by two-step sintering. It has a large piezoelectric coefficient d33 = 512 pC/N and a planner electromechanical coupling coefficient kp ≈ 0.54 at room temperature. Dielectric measurement indicates that rhombohedral-orthorhombic, orthorhombic-tetragonal, and tetragonal-cubic phase transitions upon heating process occur at −30 °C, 57 °C and 238 °C, respectively. X-ray diffraction analysis shows that the crystalline structure is dominantly of orthorhombic phase at room temperature. Domain configurations were investigated by acid etching technique. The poled ceramic shows domain patterns of long parallel stripes with hierarchical nanodomain structure existing in some broad stripes. The observed outstanding piezoelectric properties are ascribed to the rhombohedral-orthorhombic and orthorhombic-tetragonal phase transitions, and to the characteristic domain structure.

Two-level hierarchical stripe domains and enhanced piezoelectricity of rapid hot-press sintered BiFeO3 ceramics

BiFeO3 represents the most extensively investigated multiferroic due to its fascinating ferroelectric domain structures, large polarization, and multiferroic coupling, among many other emergent phenomena. Nevertheless, much less concern with the piezoelectricity has been raised while all these well addressed properties are identified in thin film BiFeO3, and bulk ceramic BiFeO3 has never been given priority of attention. In this paper, we report our experiments on the ferroelectric and piezoelectric properties as well as domain structures of BiFeO3 bulk ceramics synthesized by rapid hot-press sintering. It is revealed that these properties are strongly dependent on the microstructural quality, and the largest piezoelectric coefficient d33 = 55 pC/N with electric polarization as large as 45 μC/cm2 is obtained for the sample sintered at 800 °C, while they are only 30 pC/N and 14 μC/cm2 for the samples sintered in normal conditions at 800 °C. The two-level hierarchical stripe-like and irregular dendrite-like domain structures are observed in these hot-press sintered samples. It is suggested that the enhanced piezoelectric property is ascribed to the two-level hierarchical stripe-like domain structure which may respond more easily to electrical and strain stimuli than those irregular dendrite-like domains. The enhanced remnant polarization should be owing to the improved sample quality and large grains in the properly hot-press sintered samples.

Large Piezoelectric Effect in a Lead-Free Molecular Ferroelectric Thin Film.

Piezoelectric materials have been widely used in various applications, such as high-voltage sources, actuators, sensors, motors, frequency standard, vibration reducer, and so on. In the past decades, lead zirconate titanate (PZT) binary ferroelectric ceramics have dominated the commercial piezoelectric market due to their excellent properties near the morphotropic phase boundary (MPB), although they contain more than 60% toxic lead element. Here, we report a lead-free and one-composition molecular ferroelectric trimethylbromomethylammonium tribromomanganese(II) (TMBM-MnBr3) with a large piezoelectric coefficient d33 of 112 pC/N along polar axis, comparable with those of typically one-composition piezoceramics such as BaTiO3 along polar axis [001] (∼90 pC/N) and much greater than those of most known molecular ferroelectrics (almost below 40 pC/N). More significantly, the effective local piezoelectric coefficient of TMBM-MnBr3 films is comparable to that of its bulk crystals. In terms of ferroelectric performance, it is the low coercive voltages, combined with the multiaxial characteristic, that ensure the feasibility of piezo film applications. Based on these, along with the common superiorities of molecular ferroelectrics like light weight, flexibility, low acoustical impedance, easy and environmentally friendly processing, it will open a new avenue for the exploration of next-generation piezoelectric devices in industrial and medical applications.

Large piezoelectric performance of Sn doped BaTiO 3 ceramics deviating from quadruple point

The piezoelectric performance, both weak-signal piezoelectric coefficient d33 or large-field electrostrain, were systemically measured from room temperature until their Curie temperature. Large piezoelectric coefficient d33 of 920 pC/N was found on the boundary between the tetragonal (T) and the orthorhombic (O) phase (around 50 °C) rather than the quadruple point with lowest free energy barrier. Further simulation work based on the Landau free energy function also supported the experimental results, owing to the joint effect of the anisotropy energy and the order parameter polarization. Besides, the electrostrain of 0.15% with small hysteresis was also found on the O-T boundary. Systemically study pointed out that polarization rotation would have a significant contribution to the overall piezoelectric response.

Thermally stable piezoelectric properties of (K, Na)NbO3-based lead-free perovskite with rhombohedral-tetragonal coexisting phase

A feasible replacement for lead-based piezoelectric ceramics is desperately required for increasing environmental concerns. Benefiting from the construction of a rhombohedral-tetragonal (R-T) phase boundary, a potential lead-free candidate (Na0.5K0.5)NbO3-(Bi0.5Li0.5)TiO3-BaZrO3 is presented in this study, with a large piezoelectric coefficient d33 of 330 pC/N and a unipolar strain of 0.16% at 4 kV/mm. More importantly, the piezoresponse is extremely thermally stable that the strain can maintain a considerable value of 0.12% at the temperature as high as 190 °C, rendering the current system very promising for piezoelectric actuator applications. The temperature dependent phase structure evolution as well as piezoelectric response is investigated systematically for interpretation of underlying mechanisms.

Large piezoelectric properties in KNN-based lead-free single crystals grown by a seed-free solid-state crystal growth method

We report lead-free single crystals with a nominal formula of (K0.45Na0.55)0.96Li0.04NbO3 grown using a simple low-cost seed-free solid-state crystal growth method (SFSSCG). The crystals thus prepared can reach maximum dimensions of 6 mm × 5 mm × 2 mm and exhibit a large piezoelectric coefficient d33 of 689 pC/N. Moreover, the effective piezoelectric coefficient d33*, obtained under a unipolar electric field of 30 kV/cm, can reach 967 pm/V. The large piezoelectric response plus the high Curie temperature (TC) of 432 °C indicate that SFSSCG is an effective approach to synthesize high-performance lead-free piezoelectric single crystals.