High Piezoelectric Response Research Articles

Terraced (K, Na)NbO3 piezocatalysts with superior H2O2 production

Piezocatalytic hydrogen peroxide (H2O2) production is an emerging and green technology, but complex preparation process of piezocatalyst and low production rate limit its practical application. Herein, we propose a straightforward and efficient strategy, that is, fabricating a novel terraced potassium sodium niobate (KNN-H) by integrating high-energy pendulum ball-milling into the conventional solid-state method, to control the morphology of piezocatalyst and boost its piezocatalytic activities. By exposing a large number of edge sites with higher piezoelectric response and more active sites, KNN-H sample exhibits an extremely high H2O2 production rate of 47 μmol/h, about 35 times higher than that of previously reported potassium niobate piezocatalyst. Besides, KNN-H sample also has good effects on dye degradation and bacterial inhibition. Therefore, our strategy provides a paradigm for large-scale fabrication of high-performance perovskite piezocatalysts.

Theoretical insights into the ultrahigh piezoelectric performance of (BiFeO3)n/(BaTiO3)n (n = 1–5) superlattices

Perovskite structures have attracted extensive attention in microelectromechanical systems and nanoelectromechanical systems devices due to the high piezoelectric response and the low dielectric constant. The piezoelectric and dielectric properties of the tetragonal BiFeO3/BaTiO3 superlattices grown along the c-axis direction are investigated using density functional theory (DFT) and density functional perturbation theory. The calculated results demonstrate that the (BiFeO3)n/(BaTiO3)n (n = 1–5) superlattices exhibit a profoundly increased piezoelectric response compared to their bulk structures. The (BiFeO3)2/(BaTiO3)2 possesses the highest piezoelectric d33 of 697 pC/N among known lead-free perovskite systems. Furthermore, the (BiFeO3)2/(BaTiO3)2 superlattice possesses a low dielectric ɛ33, and its d33 at 2% tensile strain is 16 times larger than that of an unstrained equilibrium structure. This demonstrates that biaxial tensile strain significantly enhances the piezoelectric response. Combining the special quasirandom structure method with DFT, the structures of a 0.5BiFeO3–0.5BaTiO3 solid solution are predicted, and its calculated d33 is 58 pC/N, which is much smaller than that of a (BiFeO3)2/(BaTiO3)2 superlattice. The results suggest that the (BiFeO3)2/(BaTiO3)2 superlattice might be a potential candidate for nonvolatile random access memory, transducers and actuators, and nanoscale electronic devices.

A novel strategy for obtaining lead-based piezoelectric ceramics with giant piezoelectricity and high-temperature stability through the construction of “slush-like” polar states

Maintaining high piezoelectric response and piezoelectric temperature stability of lead-based piezoceramics is critical for applications under high-temperature environments. Unfortunately, the piezoelectric response of lead-based piezoceramics shows strong temperature dependence. Herein, an innovative strategy was proposed to solve this problem. The method consisted of constructing “slush-like” polar states by introducing localized heterostructures in the tetragonal phase structure to lower the energy barriers. The presence of the tetragonal phase stabilized the domain structure, providing excellent temperature stability, while the localized heterostructures also flattened the free energy landscape and enhanced the piezoelectric response. The strategy was implemented by using 0.11Pb(In0.5Nb0.5)O3-0.89Pb(Hf0.47Ti0.53)O3(PIN-PHT) piezoceramics doped with heterovalent ion Nb5+ to form a “slush-like” polar state with strong interactions inside the ceramics. The piezoelectric response and relaxor behavior of the ceramics were then investigated using piezoelectric force microscopy to reveal the mapping relationship between the complex ferroelectric domain structure and both the piezoelectric response and temperature stability. At Nb5+ doping amount of 0.8 mol%, the ceramics showed excellent comprehensive performances with d33 = 764 pC/N, Tc = 319.1 °C, εr = 3253.59, kp = 0.67, and tanδ = 0.0122. At an external ambient temperature of 300°C, the d33 of PIN-PHT-0.8Nb5+ remained high at 734 pC/N, with piezoelectric performance retention of 96.1%, showing excellent temperature stability. Overall, a new path was proposed for developing Pb-based piezoceramics with both good piezoelectric response and high-temperature stability, promising to broaden the temperature range of high-temperature piezoceramics for various applications.

High Piezoelectric Performance of KNN-Based Ceramics over a Broad Temperature Range through Crystal Orientation and Multilayer Engineering.

Uninterrupted breakthroughs in the room temperature piezoelectric properties of KNN-based piezoceramics have been witnessed over the past two decades; however, poor temperature stability presents a major challenge for KNN-based piezoelectric ceramics in their effort to replace their lead-based counterparts. Herein, to enhance temperature stability in KNN-based ceramics while preserving the high piezoelectric response, multilayer composite ceramics were fabricated using textured thick films with distinct polymorphic phase transition temperatures. The results demonstrated that the composite ceramics exhibited both outstanding piezoelectric performance (d33~467 ± 16 pC/N; S~0.17% at 40 kV/cm) and excellent temperature stability with d33 and strain variations of 9.1% and 2.9%, respectively, over a broad temperature range of 25-180 °C. This superior piezoelectric temperature stability is attributed to the inter-inhibitive piezoelectric fluctuations between the component layers, the diffused phase transition, and the stable phase structure with a rising temperature, as well as the permanent contribution of crystal orientation to piezoelectric performance over the studied temperature range. This novel strategy, which addresses the piezoelectric and strain temperature sensitivity while maintaining high performance, is well-positioned to advance the commercial application of KNN-based lead-free piezoelectric ceramics.

Giant electro-optic response in transparent rhombohedral ferroelectric Sm-PIN-PMN-PT crystal based on domain engineering

The relaxor ferroelectric crystal Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-PT), located near the morphotropic phase boundary (MPB), exhibits exceptionally high piezoelectric and electro-optic (EO) responses. Nevertheless, lower optical transparency and phase transition temperature of PMN-PT limit its optical applications. The ternary system Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 (PIN-PMN-PT) holds promise in addressing these challenges with a higher Curie temperature. Additionally, specific ferroelectric domain polarization techniques can eliminate domain scattering, substantially enhancing the transparency of the crystal. In this study, we explore the optical properties of Sm-doped PIN-PMN-PT. We achieve a 2R domain-engineered state by polarizing along the (110) direction of the crystal. The high transparency allows us to extract an effective EO coefficient of up to 431.5 pm/V from the Sm-PIN-PMN-PT crystal at the telecommunications wavelength. Second-harmonic generation (SHG) probing verified the domain-engineered state in Sm-PIN-PMN-PT. The temperature-dependent SHG reveals the ferroelectric phase transition process, laying the groundwork for studying the stability of the EO response. The Sm-PIN-PMN-PT crystal exhibits an exceptionally high EO coefficient, which is crucial for the development of enhanced EO devices with high integration and low driving voltages.

High-piezoelectric lead-free BiFeO3–BaTiO3 ceramics with enhanced temperature stability and mechanical properties

BiFeO3–BaTiO3 (BF–BT) ceramics exhibit higher piezoelectric coefficients (d33), Curie temperatures (TC), and temperature stability than other high-temperature lead-free piezoelectric materials. However, despite their crucial role in piezoelectric devices, the mechanical properties of BF–BT ceramics have been underexplored. A thorough evaluation of the mechanical properties of BF–BT is crucial for developing cost-effective and durable lead-free piezoelectric ceramics. Moreover, the specific causes of the high piezoelectric response and excellent temperature stability of BF–BT ceramics remain unclear owing to the instrumental detection threshold, which limits experimental studies to temperatures above 140 °C and below the degradation temperature of d33. To investigate the intrinsic origins of the high piezoelectricity and temperature stability of BF–xBT ceramics and to enhance their mechanical properties, a two-step sintering process is used to fabricate these ceramics (0.25 ≤ x ≤ 0.40). Owing to improvements in grain refinement and reduced Bi3+ volatilization, the BF–0.33BT ceramic exhibits enhanced overall performance, with a modified small punch strength of 155 MPa, Vickers hardness of 5.2 GPa, a d33 of 220 pC/N at room temperature, TC of 466 °C, and d33 values exceeding 400 pC/N at 260 °C. Phase-field simulations, which address the limitations of device detection thresholds, reveal that with increasing temperature, the domain structure relaxes, and polarization intensity decreases. This indicates that changes in the high-temperature piezoelectric properties can be attributed to domain structure relaxation and the increase in dielectric constant. Overall, BF–BT ceramics exhibit superior piezoelectric performance, mechanical properties, and temperature stability, making them highly suitable for use in high-temperature and demanding environments.

Wireless driven and self-sensing flexible gripper based on piezoelectric elastomer/high-entropy alloy magnetoelectric composite

The mechanical gripper shows significant importance as an alternative to manual work, but presents certain limitations in its gas or electric power with complex wire connection, presents limited available area and loud working noise, and lacks sensing function for feedback to the environment. In the present work, a novel magnetically driven and self-sensing flexible gripper was prepared based on piezoelectric elastomer and high-entropy alloy composite. The high-entropy alloy is prepared as FeCoNi(AlGa)0.5 to realize high permeability, while the piezoelectric elastomer is synthesized with superior elasticity and low modulus. The incorporation of FeCoNi(AlGa)0.5 into the piezoelectric elastomer exhibits high flexibility, magnetostriction performances and piezoelectric responses, reaching maximum strain of 1534.5 %, maximum magnetostrictive coefficient of 320 ppm and maximum piezoelectric response of 0.28 V/N. Meanwhile, the flexible gripper achieves synchronous wireless driven gripping function with a maximum lifting ratio to dead load over 41.38, and self-sensing function of target physical size with accuracy over 95 %. The flexible gripper shows maximum work power as low as 5 W. Thus, the magnetically driven and self-sensing flexible gripper shows great potential in intelligent industrial equipment.

Large Piezoelectricity Induced by Internal Stress in (K,Na)NbO3 Single Crystals.

Achieving a high piezoelectric response and excellent stability is essential for practical applications of ferroelectric materials. Herein, large piezoelectricity of d33 = 167 pC/N and kt = 0.52 is found in a K0.7Na0.3NbO3 lead-free ferroelectric single crystal without poling, which is comparable to the artificially poled KNN crystals. The large piezoelectricity is maintained up to 196 °C, showing excellent thermal stability. It was demonstrated that the high piezoelectricity is associated with strong self-polarization in the crystals. The strong internal stress formed during crystal growth gives a preferred spontaneous polarization orientation, resulting in a net macro total polarization. In addition, the internal stress also pins domain wall motions and provides a "restoring force" for the domain switching. This work provides a strategy for designing and optimizing the piezoelectric performance of ferroelectric materials.

Low-temperature co-fired PNN-PZT-based multilayer piezoelectric actuator with low cost and high reliability

Developing low-temperature co-fired MLAs for the commercial application of micro-nano actuation and manipulation has recently become a research highlight. To simultaneously achieve high piezoelectric response and low co-firing temperature below 960 °C, a PNN-PZT-0.02 Sr piezoceramic incorporated with Li2O-Bi2O3-CuO sintering additives and its MLA with the dimension of 7×7×3 mm3 were prepared using tape-casting and subsequent co-firing methods. The piezoceramic mainly composed of a triple phase (M, R, and T) co-existence shows a dense microstructure, indicating a good sintering-assistance effect. Even sintering at 920 °C, the piezoceramic possesses d33 ∼ 683 pC/N and kp ∼ 0.64, possibly surpassing most reported PZT-based piezoceramics. The MLA co-fired at 940 °C possesses a good Ag-ceramic interface without holes, aggregation or delamination. Also, it shows high maximum displacement (≥ 20 μm), high stiffness (118.5 N/μm @ 150 V), excellent thermal stability and 109-cycle reliability. A flat and defect-free electrode morphology is conducive to decreased leakage current. However, high tanδ primarily induced by the residual glassy phase and (Pb, Bi) oxides is the drawback. These findings give a novel paradigm for low-cost and high-reliability MLAs using pure Ag as inner electrodes by triple-phase controlling and nano-heterogeneity.

Effect of Nanostructure Morphology and Concentration on the Piezoelectric Performance of Flexible Pressure Sensor based on PVDFTrFE/ Nano-ZnO Composite Thin Film

Background: The development of high-performance piezoelectric pressure sensors with outstanding sensitivity, good linearity, flexibility, durability, and biocompatibility is of great significance for smart robotics, human healthcare devices, smart sensors, and electronic skin. Thus, considerable progress has been achieved in enhancing the piezoelectric property of PVDF-TrFEbased composite pressure sensors by adding various ZnO nanostructures in PVDF-TrFE polymer acting as a nucleating agent and dielectric material. Aims: In this work, flexible pressure sensors with a sandwich structure based on PVDFTrFE/ nano-ZnO composite sensing film were fabricated using a simple spin-coating method and post-annealing process, while electrospinning and high-voltage polarization processes were not adopted. Methods: Poly (vinylidene fluoride-trifluoroethylene) (PVDF-TrFE)/nano-ZnO composite films were prepared via spin coating to fabricate flexible piezoelectric pressure sensors. ZnO nanoparticles (ZnO NPs), tetrapod ZnO (T-ZnO) and ZnO nanorods (ZnO NRs) were used as nano-fillers for piezoelectric PVDF-TrFE, to enhance the beta-crystal ratio as well as the crystallinity of PVDF-TrFE. The structural and surface morphologies of the composite films were investigated using Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and scanning electron microscopy (SEM). Results: Among three different types of ZnO nanostructures with a concentration range (0-7.5 wt%), the sensor with 0.75 wt% ZnO NRs nanofiller exhibits a maximum output voltage of 1.73 V under an external pressure of 3 N and a maximum sensitivity of 586.3 mV/N at the range of 0-3 N. Further, the sensor can generate a clear piezoelectric voltage under bending and twisting deformation as well as compression and tensile deformation. Conclusion: To summarize, the addition of different concentrations of nano-ZnO can remarkably improve the piezoelectric performance of the composite sensor, and ZnO NRs can achieve better piezoelectric properties of the sensor as compared to ZnO NPs and T-ZnO. In addition, the sensor with 0.75 wt% ZnO NRs as nanofiller has the highest piezoelectric response, which is about 2.4 times that of the pure PVDF-TrFE sensor. It is demonstrated that the sensor has great potential applications in wearable health monitoring systems and mechanical stress measurement electronics.

Hybrid-DFT study of halide perovskites, an energy-efficient material under compressive pressure for piezoelectric applications

Recent studies have reported that lead-halide perovskites are the most efficient energy-harvesting materials. Regardless of their high-output energy and structural stability, lead-based products have risk factors due to their toxicity. Therefore, lead-free perovskites that offer green energy are the expected alternatives. We have taken CsGeX3 (X = Cl, Br, and I) as lead-free halide perovskites despite knowing the low power conversion rate. Herein, we have tried to study the mechanisms of enhancement of energy-harvesting capabilities involving an interplay between structure and electronic properties. A density functional theory simulation of these materials shows a decrease in the band gaps, lattice parameters, and volumes with increasing applied pressure. We report the high piezoelectric responses and high electro-mechanical conversion rates, which are intriguing for generating electricity through mechanical stress.

Strontium and Copper Co-Doped Multifunctional Calcium Phosphates: Biomimetic and Antibacterial Materials for Bone Implants.

β-tricalcium phosphate (β-TCP) is a promising material in regenerative traumatology for the creation of bone implants. Previously, it was established that doping the structure with certain cations can reduce the growth of bacterial activity. Recently, much attention has been paid to co-doped β-TCP, that is explained by their ability, on the one hand, to reduce cytotoxicity for cells of the human organism, on the other hand, to achieve a successful antibacterial effect. Sr, Cu-co-doped solid solutions of the composition Ca9.5-xSrxCu(PO4)7 was obtained by the method of solid-phase reactions. The Rietveld method of structural refinement revealed the presence of Sr2+ ions in four crystal sites: M1, M2, M3, and M4. The M5 site is completely occupied by Cu2+. Isomorphic substitution of Ca2+ → (Sr2+and Cu2+) expands the concentration limits of the existence of the solid solution with the β-TCP structure. No additional phases were formed up to x = 4.5 in Ca9.5-xSrxCu(PO4)7. Biocompatibility tests were performed on cell lines of human bone marrow mesenchymal stromal cells (hMSC), human fibroblasts (MRC-5) and osteoblasts (U-2OS). It was demonstrated that cytotoxicity exhibited a concentration dependence, along with an increase in osteogenesis and cell proliferation. Ca9.5-xSrxCu(PO4)7 powders showed significant inhibitory activity against pathogenic strains Escherichia coli and Staphylococcus aureus. Piezoelectric properties of Ca9.5-xSrxCu(PO4)7 were investigated. Possible ways to achieve high piezoelectric response are discussed. The combination of bioactive properties of Ca9.5-xSrxCu(PO4)7 renders them multifunctional materials suitable for bone substitutes.

Heart rate monitoring system based on piezoelectric poly(vinylidene fluoride-co-trifluoroethylene) composites with barium strontium titanate ceramic particles

A heart rate sensor device has been designed and developed based on a composite material based on poly(vinylidene fluoride – co – trifluoroethylene), P(VDF-TrFE) as polymer matrix and barium strontium titanate (BST) particles as ceramic fillers. The composite films were prepared by solvent casting varying the ceramic particles content between up to 40 wt%, allowing to tailor the dielectric and piezoelectric response. The morphology, polymer phase and thermal properties are independent of the ceramic filler content, whereas the dielectric constant increases significantly with increasing filler content, the largest dielectric constant, ε’ = 38 at 1 kHz, being obtained for the composite with 40 wt% of ceramic particles. Further, the highest piezoelectric response, also dependent on ceramic filler content, is |d33|= 29 pC/N, being obtained for the 10 wt% ceramic particle content film. It is also shown by piezoresponse force microscopy that higher ceramic particles are characterized by more stable ferroelectric domains. The composite has been successfully proved for its potential in heart rate monitoring applications, exhibiting high levels of precision as well as reliability. This work on heart rate sensing presents a material suitable for its incorporation into wearable gadgets, medical devices, and sports equipment, compatible with integration by printing technologies, enabling consumers to access immediate data relevant to their cardiovascular health.

On the Evolution of Stress and Microstructure in Radio Frequency-Sputtered Lead-Free (Ba,Ca)(Zr,Ti)O3 Thin Films

Thin-film piezoelectrics are widely investigated for actuators and energy harvesters, but there are few alternatives to toxic lead zirconate titanate. Biocompatible Ca- and Zr-modified BaTiO3 (BCZT) is one of the most promising lead-free alternatives due to its high piezoelectric response. However, the dielectric/piezoelectric properties and structural integrity of BCZT films, which are crucial for their applications, are strongly influenced by the substrate upon which the film is grown and the related processing methods. Here, the in-plane stress, microstructure, dielectric, and piezoelectric properties of 100–500 nm thick high-temperature RF-sputtered BCZT films on industrially relevant Si-based substrates were investigated. Obtaining polycrystalline piezoelectric films required deposition temperatures ≥ 700 °C, but this induced tensile stresses of over 1500 MPa, which caused cracking in all films thicker than 200 nm. This degraded the dielectric, piezoelectric, and ferroelectric properties of films with larger electrode areas for applications. Films on SrTiO3, on the other hand, had a compressive residual stress, with fewer defects and no cracks. The grain size and surface roughness increased with increasing deposition temperature. These findings highlight the challenges in processing BCZT films and their crucial role in advancing lead-free piezoelectric technologies for actual device applications.

Crystalline water induced nonpolar‐to‐polar transition and high piezoelectric response in lamivudine hydrate crystal

AbstractElectromechanically converted piezoelectric materials have great applications in actuators, sensors, and energy harvesters. Organic piezoelectric materials are environmentally friendly, easy to prepare, and have a low molecular mass compared to conventional inorganic piezoelectric materials. Here, we present an organic hydrogen bonding piezoelectric material, lamivudine hydrate, which crystallized in the P21 space group at room temperature and exhibits a decent d33 value of 21 pC N−1. This value is comparable to that of the commercial piezoelectric material, Tri‐Glycine Sulfate (TGS, d33=22 pC N−1). Moreover, lamivudine hydrate possesses a superior g33 value of 826×10−3 V m N−1, which is much higher than that of commercial TGS and most of the piezoelectric ceramics. While the lamivudine crystal was refined in the P43212 space group, showing no piezoelectric activity. The presence of crystalline water plays a crucial role in establishing its polar structure and achieving high piezoelectric properties of lamivudine hydrate crystal. The decent d33 and g33 values make it a promising candidate for advanced materials in high‐performance piezoelectric sensors, particularly in applications involving flexible, wearable, and biomechanical devices.

Ultrahigh Piezoelectric Response Obtained by Artificially Generating a Large Internal Bias Field in BiFeO3–BaTiO3 Lead‐Free Ceramics

AbstractPiezoelectric actuators are vital devices that convert electrical signals into mechanical strain, offering rapid and precise responses. Lead‐based piezoceramics have traditionally been the preferred choice for commercial piezoelectric actuators, while the low Curie temperature and the rising environmental concerns hinder their applications at high temperatures. In this study, a novel strategy is proposed to achieve high piezoelectric responses in lead‐free 0.67Bi1.05FeO3–0.33BaTiO3 (67BF‐33BT) ceramics with high Curie temperature by artificially generating a large internal bias field through repeat poling and aging treatments. A comprehensive exploration of how this internal bias field responds to applied electric fields and temperature variations has been conducted. The results suggest that the internal bias field originates from two aspects, one arises from the free charges that compensate for the depolarization field, while the other is attributed to the highly oriented defect dipoles. As a result of this internal bias field, the ceramics exhibit asymmetric strain–electric field (S–E) behaviors, resulting in a high strain (ε = 0.21%) and an extremely high piezoelectric coefficient (d33* = 1033.70 pm V−1) when subjected to low electric field (20 kV cm−1), along with good temperature stability from room temperature (RT) to 100 °C.

PZN-PT single crystal based high-frequency intravascular ultrasound transducers

Cardiovascular disease (CVD) is a kind of high life-threatening illness for humans. Intravascular ultrasound (IVUS) technology could highly help the physicians to know the condition of human's vessel wall. In this work, the novel lead zinc niobate-lead titanate (PZN-PT) single crystals-based IVUS transducers were prepared. The electrical properties of PZN-PT single crystals were investigated with high d33 of 2531 pC/N and dielectric constant. The high piezoelectric response could improve the transmission and receive properties of IVUS transducers. Moreover, the high dielectric constant (8050) could highly help the miniaturization of IVUS transducer. The IVUS transducers have a center frequency at 43.5 MHz and a -6dB bandwidth of 62.3%. It promising the PZN-PT based IVUS transducers are suitable for the clinical diagnosis field for CVD.

Enhancement of NiTiO3 piezocatalytic hydrogen evolution by doping with large radius elements.

Piezocatalysis is a direct method for converting mechanical vibration into chemical energy. Herein, NiTiO3 is used in the piezocatalytic hydrogen evolution field for the first time. The noncentral symmetry of NiTiO3 is enhanced by doping with large radius elements. It is demonstrated that when a metal element replaces the sites of nickel, it results in lattice distortion and a higher piezoelectric response. In particular, Cd-doped NiTiO3 exhibits the highest H2 generation rate (1.52 mmol g-1 h-1), which is 13 times that of original NiTiO3.

Orthorhombic-tetragonal phase coexistence and enhanced piezoelectric properties at room temperature in Zn and Ta modified (Ba0.95Ca0.05)(Zr0.05Ti0.95)O3 ceramics through the synergistic effect of lattice distortion.

This study provides a fundamental understanding of the enhanced piezoelectric properties in ABO3 perovskite based lead-free piezoelectric materials. For this we synthesized (Ba0.95Ca0.05)(Zr0.05Ti0.95-x (Zn1/3Ta2/3) x )O3((1 - x)BCZT-(x)ZT) (x = 0.00, 0.005, 0.01, and 0.02) solid solutions exhibiting high piezoelectric response. The (1 - x)BCZT-xZT materials are synthesized by a high-temperature solid-state ceramic reaction method by varying x in the full range (x = 0.00-0.02). In-depth exploratory research is performed on the structural, dielectric, ferroelectric, and piezoelectric properties of (1 - x)BCZT-(x)ZT ceramics. The formation of perovskite structure for all ceramics without the presence of any impurity phases is confirmed by X-ray diffraction (XRD) analyses, which also reveals that the Ca2+, Zr4+, Zr2+ and Ta5+ are well dispersed within the BaTiO3 lattice. For all (1 - x)BCZT-(x)ZT ceramics, thorough investigation of phase formation and phase-stability using XRD, Rietveld refinement, Raman spectroscopy, and temperature-dependent dielectric measurements provide conclusive evidence for the coexistence of orthorhombic + tetragonal (Amm2 + P4mm) phases at room temperature. The steady transition of Amm2 crystal symmetry to P4mm crystal symmetry with increasing x content is also demonstrated by Rietveld refinement data and related analyses. The c/a ratio of the tetragonal phase greatly influenced the electric properties of the ceramics. The c/a ratio of the tetragonal phase increases from 1.0112 for x = 0 to 1.0157 for x = 0.005 and subsequently decreases to 1.0038 for x = 0.02. When the c/a of the tetragonal phase reaches its maximum value, the ceramic with x = 0.005 has the best piezoelectricity (d 33 ∼ 297 pC N-1). The calculated degree of relaxation (γ) increases with the increase in BZT content, indicating that the BCZT-xBZT ceramics are ferroelectric materials with diffuse phase transition. Main dielectric, piezoelectric and ferroelectric parameters of (1-x)BCZT-xZT ceramics were optimized around x = 0.005 with a high piezoelectric coefficient (d 33 = 297 pC N-1), a remnant polarization (P r = 7.58 μC cm-2), spontaneous polarization (P s = 10.25 μC cm-2) and a high dielectric constant (ε max,T c = 4449 at T c and 2330 near RT) at 1 kHz, indicating promising applications for lead-free piezoelectric ceramics.

Achieving High Piezoelectric Performance across a Wide Composition Range in Tetragonal (Bi,Na)TiO3-BaTiO3 Films for Micro-electromechanical Systems.

Tetragonal (1-x)(Bi,Na)TiO3-xBaTiO3 films exhibit enhanced piezoelectric properties due to domain switching over a wide composition range. These properties were observed over a significantly wider composition range than the morphotropic phase boundary (MPB), which typically has a limited composition range of 1-2%. The polarization axis was found to be along the in-plane direction for the tetragonal composition range x = 0.06-1.0, attributed to the tensile thermal strain from the substrate during cooling after the film formation. A "two-step increase" in remanent polarization against an applied maximum electric field was observed at the high-field region due to the domain switching, and a very high piezoelectric response (effective d33 value, denoted as d33,f) over 220 pm/V was achieved for a wide composition range of x = 0.2-0.5 with high tetragonality, exceeding previously reported values for bulk ceramics. Moreover, a transverse piezoelectric coefficient, e31,f, of 19 C/m2 measured using a cantilever structure was obtained for a composition range of at least 10 atom % (for both x = 0.2 and 0.3). This value is the highest reported for Pb-free piezoelectric thin films and is comparable to the best data for Pb-based thin films. Reversible domain switching eliminates the need for conventional MPB compositions, allowing an improvement in the piezoelectric properties over a wider composition range. This strategy could provide a guideline for the development of environmentally acceptable lead-free piezoelectric films with composition-insensitive piezoelectric performance to replace Pb-based materials with MPB composition, such as PZT.