Lead-free Piezoceramics Research Articles

Enhancing core–rim structure control in (K,Na)NbO3-based lead-free piezoceramics via rapid sintering method

Core-rim structure has distinct advantage to improve the performances of KNN-based piezoceramics. Whereas the state of the core-rim structure is difficult to control during sintering. Here, the core-rim structured 0.96(K0.51Na0.47Li0.02)(Nb0.8Ta0.2)O3-0.04CaZrO3 (KNLNT) ceramics were both obtained by conventional sintering (CS) and rapid sintering (RS). KNLNT ceramics prepared by rapid sintering exhibit more outstanding controllability on grain growth and core-rim structure and can hold the core/rim size ratio in a stable and favorable level due to extended effective range of grain boundary diffusion in densification. Benefiting from the controllable microstructure, the RS method prepared samples show excellent performance. The unipolar strain value of RS-1240 (Smax=0.252%) is 2.07 times as much as CS-1110 (Smax=0.122%). Large strain, low hysteresis and low dielectric permittivity features make the core-rim structured KNLNT ceramics a potential material for pulse drive applications and demonstrate that the manual precise control of core-rim structure could create many possibilities on materials design.

Achieving ultrahigh piezoactuation constant of 2240 pm/V and giant electrostrain of 1.12% simultaneously in BNT-based polycrystalline ceramics

Ultrahigh electrostrain (Sm) at low driving field in lead-free piezoceramics could alleviate key concerns by reducing energy consumption and the risk of electrical breakdown for advanced applications. However, the giant electrostrain always accompanied with an extremely large drive field is a long-standing conflict referred as the strain-electric field trade-off. Herein, we engineer a novel strategy of introducing the B-site unequal double doping cations (ZnSn0.5)4+ into (Bi0.5Na0.5)0.93Ba0.07TiO3 ceramic to generate the spontaneous phase transition from relaxor state to ferroelectric state, polar nanoregions PNRs and defect cluster. The giant strain of Sm= 1.12% is achieved by integrating the field-induced phase transition, morphotropic phase boundary MPB and the enhanced synergistic effect between the spontaneous polarization Ps and the defect cluster polarization Pd under a low electric field of 50 kV/cm, thus yielding extremely large piezoactuation constant d33 * =2240 pm/V in (Bi0.5Na0.5)0.93Ba0.07Ti0.97(ZnSn0.5)0.03O3 piezoceramics. This finding also demonstrates an unexpected new route to design novel ferroelectric materials via nonconventional mechanisms.

Ultra-large electromechanical deformation in lead-free piezoceramics at reduced thickness.

Lead-free piezoceramics with large controllable deformations are highly desirable for numerous energy converter applications ranging from consumer electronics to medical microrobots. Although several new classes of high-performance ferroelectrics have been discovered, a universal strategy to enable various piezoceramics to realize large electromechanical deformations is still lacking. Herein, by gradually reducing the thickness from 0.5 mm to 0.1 mm, we discover that a large nominal electrostrain of ∼11.49% can be achieved in thin 0.937(Bi0.5Na0.5)TiO3-0.063BaTiO3 (BNT-BT) ceramics with highly asymmetric strain-electric field curves. Further analyses of the polarization switching process reveal that the boosted strain curves originate from the bending deformation driven by asymmetric ferroelastic switching in the surface layers. Based on this, one monolayer BNT-BT was designed to realize digital displacement actuation and a scanning mirror application with a maximum mirror deflection angle of 44.38°. Moreover, the surface effect-induced bending deformation can be extended to other piezoceramics, accompanied by derived shape retention effects. These discoveries raise the possibility of utilizing thickness engineering to design large-displacement actuators and may accelerate the development of high-performance lead-free piezoceramics.

Head-to-Head Comparison of Acoustic Properties of Lead-Free and PZT-Based HIFU Transducers Operating at 12 MHz.

A direct comparison of performance and acoustic properties of high-intensity focused ultrasonic transducers utilizing lead-free (sodium bismuth titanate-NBT) and lead-based (lead zirconate titanate-PZT) piezoceramics is discussed. All transducers operate at 12 MHz at third harmonic frequency, having an outer diameter of 20 mm, a central hole of 5 mm in diameter, and a radius of curvature of 15 mm. The electroacoustic efficiency determined by a radiation force balance is evaluated in a range of input power levels up to 15 W. Schlieren tomography as well as hydrophone measurements are used for evaluation of the acoustic field distribution. It is found that the average electroacoustic efficiency of NBT-based transducers is approximately 40%, while it is around 80% in the PZT-based devices. NBT devices show significantly higher inhomogeneity of the acoustic field under schlieren tomography compared to PZT devices. From pressure measurements in the prefocal plane, it was found that the inhomogeneity could be attributed to depoling of significant areas of the NBT piezo-component during the fabrication process. In conclusion, PZT-based devices performed significantly better than those using lead-free material. However, the NBT devices show promise for this application and their electroacoustic efficiency as well as the uniformity of the acoustic field could be improved by employing a low-temperature fabrication process or repoling after processing.

Optimized physical properties of [001]-textured (Na, K)NbO3-based lead-free piezoceramics for high power piezoelectric energy harvesters

The [001]-textured 0.96NK(N0.99S0.01)–0.01CZ–0.03BAZ piezoceramic has large kp and d33 × g33 values; therefore, the piezoelectric energy harvester fabricated using this piezoceramic exhibits a large power density.

Study on the phase structure and electrical properties of lead-free Barium titanate-based piezoelectric ceramic

Excessive Sr-doping has been observed to lead to a deterioration in the piezoelectric properties of BT-based ceramics. In response to this issue, this study introduces a solution through the development of lead-free piezoceramics using the composition (1-2x)Ba0.86Sr0.14Ti0.90Sn0.10O3-2xBa0.86Ca0.14Ti0.90Sn0.10O3 (BSTS-xBCTS), prepared through the conventional solid-state method. The rhombohedral, orthorhombic, and tetragonal phase coexistence is determined in the ceramic with 0.2≤x≤0.04. with x=0.3, the BSTS-xBCTS ceramic shows a sizeable piezoelectric property (d 33∼ 540 pC/N) and high ε r value (∼ 10280), superior or comparable to the other BT-based or lead-based ceramics. These results demonstrate that the electrical property of the BSTS-xBCTS ceramic exceeds those of some lead-based ceramics or equivalent and holds significant potential in various technological applications that require electrical materials.

Enhanced electrical properties of BNKT-BMN lead-free ceramics by CaSnO3 doping and their bioactive properties.

There is an increasing interest in using piezoelectric materials, including lead-free piezoceramics for medical applications. As a result, more attention has been placed on investigating the biological properties of these materials. In this research experiment, electrical, mechanical, and biological properties of lead-free 0.99Bi0.5(Na0.8K0.2)0.5TiO3-0.01Bi(Mg2/3Nb1/3)O3 or 0.99BNKT-0.01BMN doped with CaSnO3 (CSO) were investigated. The samples were synthesized by a modified solid-state reaction technique. X-ray diffraction (XRD) analysis showed that the samples presented a single perovskite phase. After adding CSO, electrical properties such as energy storage density (maximum W rec = 781 mJ cm-3) and electro-strain properties (maximum S max = 0.3%) were improved at room temperature. Mechanical properties were also enhanced for the modified samples with maximum values for Vickers hardness (H V) and elastic modulus (E m) of 6.11 GPa and 135 GPa, respectively. Biological assays for cytotoxicity, indicated that the samples had high cell viability, while the simulated body fluid (SBF) test revealed a moderate apatite forming ability. The samples were then coated with hydroxyapatite to improve their apatite-forming ability. The SBF testing for the coated samples showed that the coated samples had high apatite-forming ability. The obtained results pointed to the possibility of ceramics being used for multifunction electrical devices at room temperature and biomaterial applications.

Dielectric, piezoelectric and energy storage properties of Ca, Zr and Sn doped (Ba1-xCax)(Ti0.85+xZr0.02Sn0.13-x)O3 lead-free ceramics at MPB for 0.05 ≤ x ≤ 0.09

Lead-free piezoceramics based on the (Ba, Ca)(Zr, Ti)O3 (BCZT) system provide outstanding electromechanical characteristics for low-temperature actuation applications, however manufacturing temperatures are a little high. Here, we demonstrate how calcium doping can simultaneously enhance Ba(Zr, Ti, Sn)O3 piezoceramics' electromechanical strain response for the MPB composition(s) with formula (Ba1-xCax)(Ti0.85+xZr0.02Sn0.13-x)O3. The electromechanical, dielectric, and ferroelectric properties of the samples, which were created utilizing solid state synthesis techniques, were all investigated. The sample with the highest d*33 value, 748 pm/V for 0.26 kV/mm and 645 pm/V for 0.62 kV/mm, had 0.070 mol% Ca substituted on the perovskite lattice's A-site, which also demonstrated the best dielectric and piezoelectric performance in the composition range for 0.070 ≤ x ≤ 0.090. The ceramic with electromechanical coefficient (kp) = 44.6 % also displays the greatest values of large electrostrictive coefficients (Q33 ≈ 0.10 m4/C2) that also observed in these Ca, Zr and Sn doped Ba(Zr,Ti, Sn)O3 ceramics.

Deciphering the structural heterogeneity behaviors of (K, Na)NbO[formula omitted]-based piezoelectric ceramics with multi-scale analyses

Inducing local structural heterogeneity is one of the most attractive strategies to enhance the piezoelectricity in lead-free piezoceramics, while the underlying mechanisms have not been well clarified, such as phase coexistence and domain boundary. Here, we mainly focus on analyzing the structure evolution mechanism of 0.96(K0.48Na0.52)(Nb1−xSbx)O3-0.04(Bi0.5Ag0.5)ZrO3 (0≤x≤0.1) (KNN) lead-free piezoelectric ceramics to study the intrinsic structural contributions from chemical modifying and/or alloy replacement. We explore the relation between structural characteristics and physical functionality by combining macro-spectral and micro-heterogeneity characterizations. It was found that Raman- and infrared-active phonon evolutions with respect to the motion of oxygen octahedron reveal the enhanced lattice symmetry when x increases to 0.06, along with the upswing optical electronic transitions. Moreover, we clarify the local heterogeneous structure of ceramics in terms of the spatial distribution of phonon traits on the micron scale accompanied with the atom-resolution polar vector state. The detected nanoscale atomic displacement clusters are directly related to the excellent polarization properties. Additionally, the phonon thermodynamics evolution was investigated in a wide temperature range of 80-720 K with unpolarized and polarized geometries. The detailed phase transition evolution and rhombohedral–orthorhombic–tetragonal multi-phase coexistence have been confirmed with Sb incorporation. The present work boosts the understanding of the compound-structure-functionality relation of KNN-based heterophase coexistent system, which could promote the development of the promising high-performance piezoelectric materials.

BaZrO3-BaTiO3-CaTiO3 piezoceramics by a water-based mixed-oxide route: Synergetic action of attrition milling and lyophilization

This manuscript shows an innovative water-based processing route to fabricate lead-free piezoceramics. It faces the challenge of substituting conventionally used organic solvents by innocuous water. The procedure involves two methods of widespread use in industry: attrition ball-milling and freezing-lyophilization. Powders with nominal composition (Ba0.92Ca0.08)(Ti0.95Zr0.05)O3 were effectively obtained. A narrow monomodal size distribution (600 nm) proved high reactivity that allowed solid-state synthesis at ultra-low temperature (700 °C-2 h). Optimal two-step sintering method (900 °C-3 h,1280 °C-6 h) allowed well-sintered homogeneous ceramics with pure tetragonal perovskite phase. They showed high piezo-sensitivity (d33 =320 pC/N, d31 =−110 pC/N, kp =31.45% and Np =2750 kHz·mm, ε′33T=3670, tanδ=0.036 at 1 kHz), comparable to that found for routes in organic media. Therefore, attrition ball milling in water and lyophilization work in synergy to successfully activate the precursors, influencing on the structural, microstructural and electrical properties of the final BCZT ceramics. This is an unprecedented development to produce piezoelectric ceramics using a sustainable, environmentally benign water-based process, with a positive impact in noteworthy industrial applications.

Structures, dielectric properties and AC impedance characteristics of BiFeO3–BaTiO3 high-temperature lead-free piezoceramics synthesized by the hydrothermal method

Among the lead-free piezoceramics, ([Formula: see text])BiFeO[Formula: see text]BaTiO3 (BF-BT) is considered a promising candidate for high-temperature piezoelectric materials owing to its high Curie temperature ([Formula: see text]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[Formula: see text]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[Formula: see text]h, the sample obtained possesses both the lowest temperature coefficient of dielectric constant ([Formula: see text]C between RT and [Formula: see text]C) and the highest Curie temperature ([Formula: see text]C at 100[Formula: see text]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.

Dielectric and Ferroelectric Performances of Y, Mn Co-doped Barium Calcium Zirconate Titanate Based Lead-Free Piezoceramics

Dielectric and Ferroelectric Performances of Y, Mn Co-doped Barium Calcium Zirconate Titanate Based Lead-Free Piezoceramics

Superior Electromechanical Compatibility in Lead-Free Piezoceramics with Mobile Transition-Metal Defects.

Donor and acceptor ions serving as extrinsic defects in piezoelectrics are mostly used to improve the performance merits to satisfy the industrial application. However, the conventional doping strategy is unable to overcome the inherent trade-off between the piezoelectric coefficient (d33) and mechanical quality factor (Qm). Herein, inspired by the valence state variation observed in manganese oxides during sintering, this study focuses on manipulating intrinsic oxygen vacancies and extrinsic manganese defects in potassium sodium niobate (KNN) ceramics via heat treatment. The annealing process results in a simultaneous improvement in both d33 (20%) and Qm (80%), leading to comparable performance with commercial PZT-5A ceramics and enabling their application in atomizer components. Moreover, the mechanism of manganese occupation and diffusion is proposed by an extended X-ray absorption fine structure and density functional theory analysis. The improved electromechanical performance in the annealed KNN ceramic is associated with the optimized redistribution of acceptor and donor manganese defects, which is facilitated by the recombination of oxygen vacancies. This work breaks longstanding obstacles in comprehending the existing forms of manganese in KNN and offers potential in popularizing KNN-based piezoceramics to replace traditional PZT lead-based counterparts in the industrial market.

Effects of Na Excess on the Crystal Structure Ferroelectric and Piezoelectric Properties of (Bi0.487Na0.427K0.06Ba0.026)TiO3 Lead-Free Piezoceramics

In this research, (Bi0.487Na0.427K0.06Ba0.026)TiO3 ceramics were prepared by conventional solid-state mixed-oxide method to incorporate Na excess according to the chemical formula (Bi0.487Na0.427+ x K0.06Ba0.026)TiO3, where x = 0.0, 0.005, 0.010, 0.015 and 0.020. The crystal structure, dielectric, ferroelectric and piezoelectric properties were systematically investigated with respect to the amount of Na excess. X-ray diffraction data identified pure perovskite structure for all compositions. The pseudocubic structure was observed for x = 0.0 − 0.005 before it transformed to rhombohedral structure at x ≥ 0.015. The grain size tended to be larger with increasing Na excess amount. Increasing x also led to a substantial increase in ferroelectric-relaxor transition temperature (T F-R) from 80 °C (x = 0) to 110 °C (x = 0.020). With increasing x from 0 to 0.020, the standard polarization-electric field (P-E) hysteresis measurements revealed a reduction in remanent polarization (P r) together with an increase in coercive field (E c), which was further confirmed by the remanent P-E hysteresis measurements. In addition, the piezoelectric constant (d 33) was also found to steadily decrease as x increased. The observation of increased T F-R and E c along with a decrease in d 33 and P r indicated a stabilization of ferroelectric order induced by Na excess. This research highlights the importance of sufficient control over A-site stoichiometry and how it affects the ferroelectric and piezoelectric properties of BNT-based ceramics.

Optimizing Output Power Density in Lead-Free Energy-Harvesting Piezoceramics with an Entropy-Increasing Polymorphic Phase Transition Structure.

It is an urgent need to develop lead-free piezoelectric energy harvesters (PEHs) to address the energy dilemma and meet environmental protection requirements. However, the low output power densities limit further promotion of lead-free PEHs for use in daily life. Here, an entropy-increasing strategy is proposed to achieve an increased output power density of 819 μW/cm3 in lead-free potassium sodium niobate (KNN)-based piezoceramics by increasing the configuration entropy and realizing nearly two times the growth compared with low-entropy counterparts. Evolution of the energy-harvesting performance with increasing configuration entropy is demonstrated systematically, and the excellent energy-harvesting properties achieved are attributed to the enhanced lattice distortion, the flexible polarization configuration, and the high-density randomly distributed nanodomains with the entropy-increasing effect. Moreover, excellent vibration fatigue resistance and variable temperature output power characteristics were also realized in the PEH prepared by the proposed entropy-increasing material. The significant enhancement of the comprehensive energy-harvesting performance demonstrates that the construction of KNN-based ceramics with high configuration entropy represents an effective and convenient strategy to enable design of high-performance piezoceramics and thus promotes the development of advanced PEHs.

Phase structure, domain structure, thermal stability, and high-temperature piezoelectric response of BiFeO3–BaTiO3 lead-free piezoelectric ceramics

High-temperature lead-free piezoceramics with a large piezoelectric constant d33 and a high depolarization temperature Td have long been a target of ferroelectric researchers. In this work, (1-x)BiFeO3-xBaTiO3 ceramics with MnO2 and Li2CO3 additives (BF-xBT) were fabricated with traditional ceramic preparation technology. The best piezoelectric ferroelectric properties and thermal stability d33 = 185 pC/N, Pr = 33.152 μC/cm2, Tc = 470 °C, and Td = 460 °C were obtained for x = 0.32. The tetragonal (T) phase content of BF-xBT ceramics increases gradually with an increase of BT content, and the temperature stability improves. In particular, an in-situ d33 test indicates that BF-xBT ceramics have large piezoceramics coefficients with d33 = 450.5 pC/N at a temperature of T = 334 °C. Piezo force microscopy and transmission electron microscopy tests show that nanodomains and polar nanoregions play a key role in the improvement of piezoelectric response. BF-xBT ceramics appear to be the most promising candidates to replace PZT ceramics in high-temperature applications.

Superior piezoelectricity in lead-free barium titanate piezoceramics

Since the 21st century, increasing environmental protection and human health concern have been the driving force to develop lead-free piezoelectric materials with enhanced performances, and phase engineering strategy has been validated to be a viable method in numerous methodologies. Here, we gained a superb d33∼(637 ± 30) pC/N in lead-free (1–x)(Ba0.93Ca0.07)(Sn0.08Ti0.92)O3-x(Sb0.5Li0.5)TiO3 [abbreviated as (1–x)BCST-xSLT, 0 ≤ x ≤ 0.4% (in mole)] piezoelectrics utilizing chemical doping. To illustrate the relationship among composition-structure-performance, microstructure characterization, electrical properties measurement, first-principles calculation, and phase-field simulations were performed. Atomic-resolved polarization mapping of z-contrast imaging manifests the ferroelectric three phases (RO–T) coexist at the nanoscale with nanoscale polarization switching among them. Theoretical calculations and simulations confirm that the high-density nano-domain boundary bridges the polyphase coexisting nano-domains, which makes the polarization reversal easy, thus significantly reducing the energy barrier and polarization anisotropy among different phases.

Broadband ultrasonic transducer based on textured lead-free NKN-based piezoceramics

The performance of ultrasonic transducers in terms of broadband and high sensitivity is crucial for achieving excellent axial resolution and a high signal-to-noise ratio in ultrasonic imaging. These qualities greatly rely on the electromechanical properties of the piezo-materials used. In this work, a potassium sodium niobate (NKN)-based lead-free piezoceramic was fabricated by template grain growth method, resulting in outstanding electromechanical properties (d33 ≈ 710 pC N−1, k33 ≈ 0.88, kt ≈ 0.61, Tc ≈ 244 °C). A 1–3 composite structure was created using this lead-free textured ceramic to fabricate an ultrasonic transducer with a center frequency of 4.18 MHz. The ultrasonic transducer exhibited a remarkable −6 dB bandwidth of up to 140% and an insertion loss of −23.63 dB. Imaging experiments confirmed that the 1–3 NKN-based textured ceramic transducer displayed excellent −6 dB axial resolution. Notably, these performance parameters exceeded those of ultrasonic transducers made with lead-based PZT-5H piezoceramics, demonstrating the significant potential of this lead-free piezoceramic as a replacement for lead-based materials.

A suitable approach to achieve functional (Bi, Na)TiO3-based lead-free piezoceramics via compositional design for energy storage applications

A suitable approach to achieve functional (Bi, Na)TiO3-based lead-free piezoceramics via compositional design for energy storage applications

Enhanced Electromechanical Performance in Lead-free (Na,K)NbO3-Based Piezoceramics via the Synergistic Design of Texture Engineering and Sm-Modification.

Next-generation electromechanical conversion devices have a significant demand for high-performance lead-free piezoelectric materials to meet environmentally friendly requirements. However, the low electromechanical properties of lead-free piezoceramics limit their application in high-end transducer applications. In this work, a 0.96K0.48Na0.52Nb0.96Sb0.04O3-0.04(Bi0.5-xSmx)Na0.5ZrO3 (abbreviated as T-NKN-xSm) ceramic was designed through phase regulation and texture engineering, which is expected to solve this difficulty. Through our research, we successfully demonstrated the enhanced electromechanical performance of lead-free textured ceramics with a highly oriented [001]c orientation. Notably, the T-NKN-xSm textured ceramics doped with 0.05 mol % Sm exhibited the optimal electromechanical performance: piezoelectric coefficient d33 ≈ 710 pC N-1, longitudinal electromechanical coupling k33 ≈ 0.88, planar electromechanical coupling kp ≈ 0.80, and Curie temperature Tc ≈ 244 °C. Finally, we conducted a detailed investigation into the phase and domain structures of the T-NKN-Sm ceramics, providing valuable insights for achieving high electromechanical properties in NKN-based ceramics. This research serves as a crucial reference for the development of advanced electromechanical devices by facilitating the utilization of lead-free piezoelectric materials with superior performance and environmental benefits.