Large-signal Piezoelectric Coefficient Research Articles

Achieving enhanced piezoelectric properties in BiFeO3-PbTiO3 based ceramics by a synergistic effects of texturing and structure engineering in reactive template grain growth-like process

A synergistic strategy of texturing and structure engineering in reactive template grain growth-like process has been validated on fabricating 0.66Bi0.9Sm0.1FeO3-0.34PbTiO3 piezoelectric ceramics with enhanced properties. A considerable texture degree is successfully obtained by optimizing sintering conditions. The template is fully dissolved into the matrix after sintering, driving a structure transformation from rhombohedral to pseudo-cubic phase. In comparison to its non-textured counterpart, the textured ceramics show a 69 % increase on large-signal piezoelectric coefficient d33* and a 43 % increase on small-signal piezoelectric coefficient d33. Good high temperature piezoelectric performance is also revealed. At 225 °C, the maximum strain and calculated d33* are 0.22 % and 436 pm/V, respectively, which increase by 49 % compared with corresponding parameters at room temperature. The study not only signify a promising strategy to design high performance BFO based functional materials, but also broaden the scope of texture technology in the development of piezoelectric ceramics.

Electromechanical properties of BS-PT ceramics under uniaxial pressure and hydrostatic pressure

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.

Large electrostrain achieved in BNKT‐based ceramics by the adjustment of phase boundary with Ba(Sn0.70Nb0.24)O3 addition

AbstractIn the current study, the incorporation of Ba(Sn0.70Nb0.24)O3 (BSN) effectively modifies the phase boundary of the 0.8(Bi0.50Na0.50)TiO3‐0.2(Bi0.50K0.50)TiO3 (BNKT) lead‐free ceramic material, inducing enhanced electrostrain properties at room temperature, particularly results in a “bud‐like” strain profile without negative strain. A comprehensive investigation has been conducted into the microstructure, electrical properties, and electrostrain properties of the above‐mentioned ceramics. The addition of BSN was observed to be well incorporated into the BNKT crystal structure, forming a single perovskite structure according to the X‐ray diffraction pattern. With the increase in BSN solid solution content, the temperature at which the transition from ferroelectric to the relaxor phase occurs shifted from 88.1°C to beneath room temperature (30°C). Specifically, the BNKT‐0.0075BSN ceramic demonstrated a positive strain response of 0.459% along with a large signal piezoelectric coefficient (d33*) of 643 pm/V. Additionally, the strain hysteresis of the BNKT‐0.0175BSN ceramics was only about 3% at 120°C. These experimental findings suggest that BNKT‐xBSN ceramics could be strong contenders for actuators and sensors, presenting promising opportunities for lead‐free ceramic actuator applications.

Superior Large-Signal Piezoelectric Coefficient in Textured NBT-Based Piezoceramics by Template-Induced Structure and Composition Modulation.

The field-induced-phase transition in (Na1/2Bi1/2)TiO3-based lead-free piezoceramics can be facilitated in the ⟨001⟩-crystallographic orientation, and the templated grain growth is an effective method to align polycrystalline ceramics along with specific directions. However, due to the low texturing degree and undesirable composite effect of the added templates, the textured ceramics using the templated grain growth (TGG) method usually require a higher driving field to trigger the phase transition instead. Here, ⟨001⟩-textured (Na0.5Bi0.5)0.935Ba0.065Ti0.978(Fe0.5Nb0.5)0.022O3 ceramics are prepared through a liquid-phase-assisted TGG process at a low sintering temperature (1000 °C), in which the NaNbO3 (NN) templates induce a strong crystallographic anisotropic structure (a high Lotgering factor of 95%) while dissolving into oriented grains. The dissolution of templates acts as a composition doping and contributes to reducing the driving electric field as proven by the phase-field simulation analysis. Furthermore, electrical and structural characterizations reveal that an increased ionic disorder occurs in the textured ceramic, causing highly dynamic polar nanoregions and a larger reversible phase transition. Thanks to the appropriate structure/composition control, the textured ceramic achieves a large d33* value of 907 pm/V at 40 kV/cm. The high-performance lead-free ceramic under low driving electric field benefits the development of multilayer piezoelectric actuators.

Enhanced Piezoelectricity and Thermal Stability of Electrostrain Performance in BiFeO3-Based Lead-Free Ceramics

BiFeO3-based ceramics possess an advantage over large spontaneous polarization and high Curie temperature, and are thus widely explored in the field of high-temperature lead-free piezoelectrics and actuators. However, poor piezoelectricity/resistivity and thermal stability of electrostrain make them less competitive. To address this problem, (1 - x) (0.65BiFeO3-0.35BaTiO3)-xLa0.5Na0.5TiO3 (BF-BT-xLNT) systems are designed in this work. It is found that piezoelectricity is significantly improved with LNT addition, which is contributed by the phase boundary effect of rhombohedral and pseudocubic phase coexistence. The small-signal and large-signal piezoelectric coefficient (d33 and d33*) peaks at x = 0.02 with 97 pC/N and 303 pm/V, respectively. The relaxor property and resistivity are enhanced as well. This is verified by Rietveld refinement, dielectric/impedance spectroscopy and piezoelectric force microscopy (PFM) technique. Interestingly, a good thermal stability of electrostrain is obtained at x = 0.04 composition with fluctuation η = 31% (Smax'-SRTSRT×100%), in a wide temperature range of 25-180 °C, which is considered as a compromise of negative temperature dependent electrostrain for relaxors and the positive one for ferroelectric matrix. This work provides an implication for designing high-temperature piezoelectrics and stable electrostrain materials.

Giant electro-strain nearly 1% in BiFeO3-based lead-free piezoelectric ceramics through coupling morphotropic phase boundary with defect engineering

Ultrahigh strain and large piezoelectric coefficient in ferroelectric ceramics are always desired for actuator application. However, a long-standing challenge is the reported electro-strain value in lead-free ceramics encountering a bottleneck of 0.8%. Meanwhile, ultrahigh strain requires sufficiently high electric field, thus leading to the incompatibility of large strain with a low large-signal piezoelectric coefficient d33∗. In this work, we report a novel material design strategy that coupling morphotropic phase boundary and defect engineering realize a giant recoverable electro-strain nearly 1.0% and a large-signal piezoelectric coefficient d33∗ = 1212.5 pm/V in 0.695BiFeO3–0.3BaTiO3–0.005Bi(Zn0.5Ti0.5)O3 ceramic, which is the largest strain value so far in reported lead-free ceramics. Structural investigations reveal that this electro-strain is tightly associated with the abundant polar nanoregions (PNRs) in phase boundary and internal bias field induced by defect dipoles via eliminating negative strain combining with asymmetric strain behavior. The coexistent phases and their PNRs with increasing structural flexibility as well as internal bias field aiding polarization orientation are responsible for the extremely high piezoelectric response. This work will afford a paradigm to optimize the strain properties and stimulate new development of lead-free oxides for actuators applications.

Investigating the importance of strain-coupling in lead-free 2–2 relaxor/ferroelectric composites with digital image correlation

Ceramic–ceramic composite structures are a viable solution to improve the electromechanical response of lead-free ferroelectrics (FEs) through tuning of the local electrical and mechanical fields. The origin of the enhanced properties, however, remains unclear, as many of the possible effects, such as polarization and strain coupling (PSC) as well as interface diffusion, are interrelated and difficult to separate or directly investigate. In this study, we use a custom-built digital image correlation system to directly investigate the influence of strain coupling on 2–2 composites consisting of 0.90Na1/2Bi1/2TiO3–0.06BaTiO3–0.04K0.5Na0.5NbO3 (NBT–6BT–4KNN) and 0.94Na1/2Bi1/2TiO3–0.06BaTiO3 (NBT–6BT) by varying the mechanical interface contacts between end members. Specifically, two model cases were utilized to separate the relative contributions of the PSC mechanisms: (a) electrically connected and (b) mechanically and electrically connected. The local strain gradient was characterized through the thickness of the composite across different layers as well as the interface, where the macroscopic large signal longitudinal and transverse FE response was determined. Experimental results reveal an enhancement of the large signal piezoelectric coefficient by approximately 10% from 390 to 440 pm V−1 due to strain coupling.

Novel lead-free BCZT-based ceramic with thermally-stable recovered energy density and increased energy storage efficiency

The eco-responsible lead-free piezoelectric ceramics have been intensively searched for more than a decade, however, the final goal to replace toxic ceramics like lead zirconate titanate (PZT) with lead-free compounds, having comparable or even better performance has not yet been reached. In this road, the lead-free ceramics Ba0.85Ca0.15Zr0.1Ti0.9O3 (BCZT), possessing excellent dielectric, ferroelectric, and piezoelectric properties are regarded as serious candidates for the PZT replacement. Besides, nanostructuring BCZT is of paramount importance to enhance these functionalities even more. Here, BCZT multipodes are designed by template-growth hydrothermal synthesis using hydrogen zirconate titanate nanowires. We demonstrate that the fabricated BCZT multipodes exhibit high dielectric permittivity of 5300 with a temperature stability coefficient of ±5.9% between 20 and 140 °C. A significant recovered energy density of 315.0 mJ/cm3 with high thermal stability and high energy storage efficiency of 87.4%, and enhanced large-signal piezoelectric coefficient d33∗ (310 pm/V) are found. Compared to the traditional BCZT ceramics reported in the literature, relying on high-temperature processing, our sample exhibits boosted energy storage parameters at a much lower temperature. These outcomes may offer a new strategy to tailor eco-responsible relaxor ferroelectrics toward superior energy storage performance for ceramic capacitor applications.

Control of polarization in bulk ferroelectrics by mechanical dislocation imprint.

Defects are essential to engineering the properties of functional materials ranging from semiconductors and superconductors to ferroics. Whereas point defects have been widely exploited, dislocations are commonly viewed as problematic for functional materials and not as a microstructural tool. We developed a method for mechanically imprinting dislocation networks that favorably skew the domain structure in bulk ferroelectrics and thereby tame the large switching polarization and make it available for functional harvesting. The resulting microstructure yields a strong mechanical restoring force to revert electric field-induced domain wall displacement on the macroscopic level and high pinning force on the local level. This induces a giant increase of the dielectric and electromechanical response at intermediate electric fields in barium titanate [electric field-dependent permittivity (ε33) ≈ 5800 and large-signal piezoelectric coefficient (d 33*) ≈ 1890 picometers/volt]. Dislocation-based anisotropy delivers a different suite of tools with which to tailor functional materials.

Origin of large electric-field-induced strain in pseudo-cubic BiFeO3–BaTiO3 ceramics

High-performance lead-free piezoelectric materials are in great demand for actuator applications replacing the mainstay Pb(Zr, Ti)O3 materials. In this research, pseudo-cubic 0.64BiFeO3–0.36BaTiO3 (0.64BF–0.36BT) lead-free ceramics were studied, exhibiting high electric-field-induced strain of 0.38% (60 kV/cm) with large signal piezoelectric coefficient d33* of 720 pm/V (40 kV/cm) and low strain hysteresis of 8% at 150 °C. It is important that the strain (40 kV/cm) of prototypic co-fired multilayer actuator is found to increase from 0.22% to 0.3% at elevated temperature of 150 °C, accompanied by a significantly decreased strain hysteresis. The behind mechanism of the large unipolar strain was investigated by in-situ synchrotron powder X-ray diffraction under different electric fields, being analogous to (Bi, Na)TiO3-BaTiO3 based ceramics but different from Pb(Zr,Ti)O3 based counterparts. An evident transition from pseudo-cubic to rhombohedral phase was triggered above electric field of 10 kV/cm, where the lattice distortion, domain switching and phase transition synergistically contribute to the observed large macrostrain. These results demonstrate that the lead-free BiFeO3–BaTiO3 ferroelectric ceramics with pseudo-cubic phase have great potential for high temperature actuator applications.

High energy storage efficiency and large electrocaloric effect in lead-free BaTi0.89Sn0.11O3 ceramic

Lead-free BaTi0.89Sn0.11O3 (BTSn) ceramic was elaborated via a solid-state reaction method and its dielectric, ferroelectric, energy storage, electromechanical as well as electrocaloric properties were investigated at 25 kV/cm. Pure perovskite structure was confirmed by X-ray diffraction analysis. The maximum of the dielectric constant was found to be 17390 at 41 °C. The enhanced total energy density, the recovered energy density, and the energy storage efficiency of 92.7 mJ/cm3, 84.4 mJ/cm3, and 91.04 %, respectively, were observed at 60 °C. In contrast, the highest energy storage efficiency of 95.87 % was obtained at 100 °C. At room temperature, the electromechanical strain and the large-signal piezoelectric coefficient reached a maximum of 0.07 % and 280 pm/V. The large electrocaloric effect of 0.71 K and the electrocaloric responsivity of 0.28 × 10-6 K mm/kV at 49 °C under 25 kV/cm were indirectly determined via Maxwell approach and the measured ferroelectric polarization P(E,T). The electrocaloric response was also modelled by exploiting the Landau-Ginzburg-Devonshire (LGD) phenomenological theory. The modelling result of 0.61 K at 50 °C under 25 kV/cm supports the experimental findings. We conclude that BTSn lead-free ceramic is a promising candidate for potential applications in high-efficiency energy storage devices and solid-state refrigeration technology.

Temperature Dependent Piezoelectric Properties of Lead-Free (1-x)K0.6Na0.4NbO3–xBiFeO3 Ceramics

(1-x)K0.4Na0.6NbO3–xBiFeO3 lead-free piezoelectric ceramics were successfully prepared in a single perovskite phase using the conventional solid-state synthesis. Relative permittivity (er) as a function of temperature indicated that small additions of BiFeO3 not only broadened and lowered the cubic to tetragonal phase transition (TC) but also shifted the tetragonal to orthorhombic phase transition (TO–T) toward room temperature (RT). Ceramics with x = 1 mol.% showed optimum properties with small and large signal piezoelectric coefficient, d33 = 182 pC/N and d∗33 = 250 pm/V, respectively, electromechanical coupling coefficient, kp = 50%, and TC = 355°C. kp varied by ∼5% from RT to 90°C, while d∗33 showed a variation of ∼15% from RT to 75°C, indicating that piezoelectric properties were stable with temperature in the orthorhombic phase field. However, above the onset of TO–T, the properties monotonically degraded in the tetragonal phase field as TC was approached.

Ultra-large electric field-induced strain in potassium sodium niobate crystals.

Electromechanical coupling in piezoelectric materials allows direct conversion of electrical energy into mechanical energy and vice versa. Here, we demonstrate lead-free (K x Na1-x )NbO3 single crystals with an ultrahigh large-signal piezoelectric coefficient d 33* of 9000 pm V-1, which is superior to the highest value reported in state-of-the-art lead-based single crystals (~2500 pm V-1). The enhanced electromechanical properties in our crystals are realized by an engineered compositional gradient in the as-grown crystal, allowing notable reversible non-180° domain wall motion. Moreover, our crystals exhibit temperature-insensitive strain performance within the temperature range of 25°C to 125°C. The enhanced temperature stability of the response also allows the materials to be used in a wider range of applications that exceed the temperature limits of current lead-based piezoelectric crystals.

Low- and high-field electromechanical responses of relaxor-based multicomponent ceramics for application in multiregime actuators

The electromechanical responses of multicomponent solid solutions [Formula: see text][Formula: see text]([Formula: see text][Formula: see text])[Formula: see text]([Formula: see text][Formula: see text])[Formula: see text]([Formula: see text][Formula: see text])[Formula: see text][Formula: see text]O3in low and high electric fields were studied. In both cases, significant electromechanical responses are observed. In particular, the maximum values of the large-signal piezoelectric coefficient [Formula: see text] reach 1600[Formula: see text]m/V at very low values of the electric field ([Formula: see text]5[Formula: see text]kV/cm). The observed features of the electromechanical responses of the studied ceramics are advantages in terms of their possible application in actuators.

Tailoring the strain performance of lead-free relaxor/ferroelectric-layered composites

0.95(Na0.82K0.18)1/2Bi1/2TiO3–0.05FeNbO4 (NKBT-0.05FN) lead-free incipient piezoceramic is a promising candidate for actuator applications due to their large reversible electromechanical strains. However, the driving electric field required to obtain such a large strain is too high to meet the requirements of commercial applications. In this study, 0.95(Na0.82K0.18)1/2Bi1/2TiO3–0.05FeNbO4 /(Na0.82K0.18)1/2Bi1/2TiO3 (NKBT-0.05FN/NKBT) relaxor/ferroelectric (RE/FE) 2–2 type composite ceramics were designed to produce tailored strain properties. By tailoring the phase structure of the composites, a high strain of 0.36% and the corresponding large-signal piezoelectric coefficient d*33 of 720 pm/V were achieved using 90 vol.% NKBT-0.05FN/10 vol.% NKBT under a low driving electric field of 50 kV/cm.

Giant electro‐strain in textured Li+‐doped 0.852BNT–0.11BKT–0.038BT ternary lead‐free piezoelectric ceramics

AbstractTexturing is an effective approach to improving the piezoelectricity of piezoelectric ceramics. In this work, <001> textured Li+‐doped 0.852Bi0.5Na0.5TiO3–0.11Bi0.5K0.5TiO3–0.038BaTiO3 ternary lead‐free piezoelectric ceramics are prepared by the reactive templates grain growth (RTGG) method. X‐ray diffraction (XRD) results demonstrate a high orientation degree of 77% along the <001> direction. Outstanding electro‐strain response, which is higher than most of reported BNT‐based textured ceramics, is achieved due to the contribution of oriented‐grains along the <001> direction. A large electro‐strain of 0.55% with a relatively low hysteresis is obtained at 6.5 kV/mm with corresponding large signal piezoelectric coefficient () of 846 pm/V in the textured ceramics, which is 49% higher than that of the random ceramics. Besides, the electro‐strain could reach as high as 0.52%@5.5 kV/mm ( = 945 pm/V) at 100°C. These results indicate that the RTGG is an effective way to design high performance lead‐free piezoelectric materials.

Dielectric and Piezoelectric Properties of Textured Lead-Free Na0.5Bi0.5TiO3-Based Ceramics

This work provides a comparative study of the dielectric and piezoelectric properties of randomly oriented and textured 0.88Na0.5Bi0.5TiO3-0.08K0.5Bi0.5TiO3-0.04BaTiO3 (88NBT) ceramics. Textured ceramics were fabricated by template grain growth (TGG) method using NaNbO3 (NN) for templates. For textured ceramics with 4 wt% NN templates, a Lotgering factor of 96% and piezoelectric coefficient d33 of 185 pC/N were obtained. Compared to the randomly oriented ceramics, textured ceramics show lower strain hysteresis (H = 7.6%), higher unipolar strain of 0.041% with corresponding large signal piezoelectric coefficient d33* of 200 pm/V at applied field of 2 kV/mm. This enhancement can be explained by the grain orientation along <001> direction by texturing, where an engineered domain configuration is formed after polarization, leading to decreased hysteresis and increased piezoelectric property.

Low-temperature sintered (Na1/2Bi1/2)TiO3-based incipient piezoceramics for co-fired multilayer actuator application

Low-temperature sintered (Na1/2Bi1/2)0.935Ba0.065Ti0.975(Fe1/2Nb1/2)0.025O3 (NBT-BT-0.025FN) lead-free incipient piezoceramics were investigated using high-purity Li2CO3 as sintering aids. With the ≤0.5 wt% Li2CO3 addition, the introduced Li+ cations precede to enter the A-sites of the perovskite lattice to compensate for the A-site deficiencies. Once the addition exceeds 0.5 wt%, the excess Li+ cations will occupy B-sites and give rise to the generation of oxygen vacancies, which accelerate the mass transport and thus lower the sintering temperature effectively from 1100 °C down to 925 °C. It was also found that a small amount of Li+ addition has little effect on the phase structure and electromechanical properties of the system, but overweight seriously disturbs these characteristics because of the large lattice distortion. The sintered NBT-BT-0.025FN incipient piezoceramics with 1.25 wt% Li2CO3 addition at 925 °C provides a large strain of 0.33% and a corresponding large signal piezoelectric coefficient d*33 of 550 pm/V at 60 kV/cm, indicating this system is a very promising candidate for lead-free co-fired multilayer actuator application.

Novel bismuth ferrite-based lead-free incipient piezoceramics with high electromechanical response

Lead-free piezoceramics with high recoverable strain (or d33*, the large-signal piezoelectric coefficient) and a low degree of hysteresis (Hys) are in great demand for next-generation actuator devices to meet the requirement of sustainable development.

Phase‐Field Study of Electromechanical Coupling in Lead‐Free Relaxor/Ferroelectric‐Layered Composites

The interface coupling effect of multilayer lead‐free ceramic/ceramic relaxor/ferroelectric composites is studied by finite element–based phase‐field simulations. The macroscopic electromechanical behavior of such composite systems is influenced by both polarization and strain coupling through the electrical and mechanical interaction of connected layers. Separating such interconnected phenomena is difficult experimentally. Here, we direct investigate different coupling effect by introducing soft and charge interphase layers in the serial‐type layer composite model. The large strain response of the composite results from the electric field–induced nonpolar–polar phase transition of the relaxor constituent. A new relaxor phase‐field model is first developed to reproduce this phase transition and parameterized by fitting the measured hysteresis loops. It is then directly compared to the experimental results of the serial‐type composite composed of 0.91Bi1/2Na1/2TiO3–0.06BaTiO3–0.03AgNbO3 and 0.93Bi1/2Na1/2TiO3–0.07BaTiO3. Results show that the lateral strain coupling in the serial layer contributes considerably to the large signal piezoelectric coefficient . The primary enhancement in is due a reduction in the remanent strain of the ferroelectric layer caused by the lateral mismatch. Moreover, charge interphase layers in the composite can introduce an internal electric field, leading to a weaker large‐signal response compared with the composite with coherent interfaces.