High-performance Piezoelectric Materials Research Articles

Low-Cost, High-Performance Piezoelectric Nanocomposite for Mechanical Energy Harvesting

Lack of low-cost, large area deposition methods and photo-patternability of high-performance piezoelectric materials restrict the rapid development of efficient functional devices like sensors and energy harvesters. In this paper, we report an optimized process flow for Zinc Oxide (ZnO)/SU-8 and Barium Titanate (BTO)/SU-8 based nanocomposite thin films for mechanical energy harvesting (MEH) applications. Parametric variation of process variables for these nanocomposites reveals that 15% ZnO/SU-8 and 20% BTO/SU-8 nanocomposites show optimum results with good piezoelectric response and UV transmittance, allowing reliable lithography of the nanocomposites. Furthermore, three different types of energy harvesting devices are fabricated using these nanocomposites as piezoelectric layer. Output powers of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$223~\mu \text{W}$ </tex-math></inline-formula> (ZnO/SU-8) and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$642~\mu \text{W}$ </tex-math></inline-formula> (BTO/SU-8) are produced at resonance for the conventional cantilever type MEH devices at an input acceleration of 0.5g. Using the nanocomposites as flexible nanogenerator, open circuit voltages of 570 mV (ZnO/SU-8) and 780mV (BTO/SU-8) are obtained using regular finger pressing. The hybrid energy harvesters, based on combined piezoelectric-triboelectric transduction mechanisms, generate output voltages of 0.4V, 0.95V, 1.4V (ZnO/SU-8) and 0.7V, 1.1V and 1.9V (BTO/SU-8) in piezoelectric, triboelectric and hybrid operations, respectively.

Large electrostrain with nearly-vanished hysteresis in eco-friendly perovskites by building coexistent glasses near quadruple point

One of the key questions in the development of eco-friendly piezoelectrics lies in how to achieve large hysteresis-free electrostrain responses in a facile and effective manner, to meet the requirements of high-precision electromechanical devices. Here, through integrating phase-field modeling and experimental approach, a highly effective strategy is proposed for large electrostrain outputs with negligible hysteresis in lead-free perovskite oxide ferroelectrics, by building coexistent glasses with diverse local symmetries near a quadruple point rendering low energy barriers between different polar states. Guided by phase-field simulations, a superior electrostrain of ~ 0.21% with nearly-zero hysteresis is obtained at the constructed glasses region near the quadruple point of Bi-doped Ba(Zr0.2Ti0.8)O3-x(Ba0.7Ca0.3)TiO3 ceramics, outperforming almost state-of-the-art lead-free piezoelectric substitutions when taking both electrostrain and hysteresis into account. The strategy of building coexistent glasses near the quadruple point provides a novel design paradigm for high-performance piezoelectric materials in the application of high-precision actuators.

Structural origin for the high piezoelectric performance of (Na0.5Bi0.5)TiO3-BaTiO3-BiAlO3 lead-free ceramics

Achieving high piezoelectric performance in the representative lead-free materials of Bi1/2Na1/2TiO3-BaTiO3 (BNT-BT) is of great interest. However, it remains a challenge in these materials, as they feature structural phases with strong octahedral tilting at morphotropic phase boundary (MPB). Herein, we obtain good piezoelectric performance with relatively large d33 value (219 pC/N), small coercive field (1.5 kV/mm), and good thermal stability in the (1-x)(Na0.5Bi0.5)TiO3-x(0.9BaTiO3-0.1BiAlO3) ternary system by crystal structure design. It is found that the incorporation of BiAlO3 with large tolerance factor can suppress the octahedral tilting and reduce the structural distortion of R3c and P4bm at MPB, and thus allows the electric field induced an extensive and reversible phase transformation. By using in-situ electric field synchrotron X-ray diffraction, it is revealed that the crystal lattice of the R3c phase with a smaller structural distortion responds more flexible to the electric field than that of the P4bm phase with a larger structural distortion. The piezoelectric strain analysis through profiles fitting indicates that the enhanced piezoelectric response attributed to both the activated domain switching and enhanced lattice strain benefited from the subtle phase structure. These findings provide further insights into the dynamic structural response of BNT-based materials, and will be helpful in designing high-performance piezoelectric materials beyond the MPB.

B-AB24-02 PIEZOELECTRIC ENERGY HARVESTING FOR PACEMAKERS

Battery depletion is the leading cause of cardiac AICD pacemaker replacement. Auto-recharging via energy harvesting (EH) is a technique that could eliminate battery replacement. Piezoelectric EH converts mechanical energy into electrical energy. Research investigating EH for implantable medical devices is limited, and most approaches require additional surgery for attachment to the epicardium. To evaluate the use of piezoelectric coatings on transvenous leads and leadless pacemakers for EH without impacting the implantation procedure. In 15 in vivo porcine hearts we tested 5 piezoelectric materials and 7 device configurations. The devices were implanted into the RV and the effects of insertion location, heart rate, and RV contractility on the piezoelectric voltage output were investigated. The animals were paced at a heart rate of 80 to 140 bpm and iv dobutamine was used to increase heart contractility. Voltage outputs and power density were shown to increase with better performing piezoelectric materials and using device designs that amplified the mechanical inputs from heart contraction and relaxation. Estimate power density for the best performing device on a lead and leadless pacemaker was 10 μW/cm3 and 5 μW/cm3, respectively. We conclude that material selection and device design affect the EH capabilities of the coatings. Power densities of the devices are approaching that of typical pacemaker batteries of 25 μW/cm3. Future studies will investigate increasing outputs using a variety of approaches including multi-layer structures, mechanical amplification, and high-performance piezoelectric materials.

Polarization rotation boosts strong piezoelectric response in the lead-free perovskite ferroelectric K0.5Na0.5NbO3

Polarization rotation is considered one of the most important intrinsic origins of high piezoelectricity in perovskite ferroelectrics. Such rotation strongly increases the lateral polarization, thus giving rise to the ultrahigh-shear piezoelectric coefficient. The evolution of polarization vector as a function of shear strain in a lead-free perovskite ferroelectric, ${\mathrm{K}}_{0.5}{\mathrm{Na}}_{0.5}{\mathrm{NbO}}_{3}$ (KNN), is demonstrated using the first-principle calculations. The polarization rotation is found to correlate directly with the shear piezoelectric constant. The larger the rotation angle, the higher the shear piezoelectric constant. The atomic insight reveals the polarization rotation mainly relies on the reorientation of Nb and O atoms along low potential-energy surfaces. We propose the polarization vector is more likely to rotate along the ${[111]}_{\mathrm{PC}}\ensuremath{\rightarrow}{[101]}_{\mathrm{PC}}\ensuremath{\rightarrow}{[001]}_{\mathrm{PC}}$ path instead of direct ${[111]}_{\mathrm{PC}}\ensuremath{\rightarrow}{[001]}_{\mathrm{PC}}$ transition in high-performance lead-free piezoelectric materials with broad thermotropic phase boundaries; thus, the critical role of orthorhombic structure should be emphasized. We hope that this work will inspire future experimental studies for further developing lead-free piezoelectric materials.

Quantitative mapping of nanotwin variants in the bulk

Crystallographic twins are critical to the properties of numerous materials from magnesium alloys to piezoelectrics. Since the onset of the twin formation is highly sensitive to the triaxial mechanical boundary conditions, non-destructive bulk microscopy techniques are required. Elastic strains can be mapped via X-ray diffraction with a 100-200 nm resolution. However, the interplay of strains with nanotwins cannot be characterized. Here, a method based on dark-field X-ray microscopy to quantify the density of nanotwin variants with twin lamellae of sizes as small as several tens of nanometers in embedded subvolumes (70x200x600 nm3) in millimeter-sized samples is introduced. The methodology is corroborated by correlating the local density of twin variants to the long-ranging strain fields for a high-performance piezoelectric material. The method facilitates direct, in situ mapping and quantification of nanoscale structural changes together with their elastic driving fields, which is the key towards controlling and engineering material's performance at nanometric scales.

Enhanced piezoelectric response in ferroelectric solid solution with rhombohedral end members

High-performance piezoelectric materials are, in general, ferroelectric solid solutions exhibiting morphotropic phase boundaries (MPB) – a composition driven interferroelectric instabilities. The most common approach to engineer MPB in ferroelectric systems is to choose the end members of the solid solution with different polar symmetries and anticipate for the interferroelectric transformation to occur around a certain critical composition. Here I report a non-classical approach of obtaining MPB by choosing end members of solid solutions with similar polar symmetry (rhombohedral). This is demonstrated in the alloy system x(Na0.5Bi0.5)TiO3–(1-x)Pb(Zr0.6Ti0.4)O3 (NBT-PZT) which shows a narrow MPB region (0.07 ≤ .x ≤ 0.10) at which the piezoelectric response increases remarkably by nearly 3-times to its parent end members. This strategy opens the possibility of discovering new MPB ferroelectric systems with an enhanced electromechanical response.

Scalable Fabrication of High-Performance Thin-Shell Oxide Nanoarchitected Materials via Proximity-Field Nanopatterning.

Nanoarchitected materials are considered as a promising research field, deriving distinctive mechanical properties by combining nanomechanical size effects with conventional structural engineering. Despite the successful demonstration of the superiority and feasibility of nanoarchitected materials, scalable and facile fabrication techniques capable of macroscopically producing such materials at a low cost are required to take advantage of the nanoarchitected materials for specific applications. Unlike conventional techniques, proximity-field nanopatterning (PnP) is capable of simultaneously obtaining high spatial resolution and mass producibility in synthesizing such nanoarchitected materials in the form of an inch-scale film. Herein, we focus on the feasibility of using PnP as a scalable fabrication technique for three-dimensional nanostructures and the superiority of the resultant thin-shell oxide nanoarchitected materials for specific applications, such as lightweight structural materials, mechanically robust nanocomposites, and high-performance piezoelectric materials. This review will discuss and summarize the relevant results obtained for nanoarchitected materials synthesized by PnP and provide suggestions for future research directions for scalable manufacturing and application.

Fine-grained relaxor ferroelectric PMN-PT ceramics prepared using hot-press sintering method

Relaxor ferroelectric PbMg1/3Nb2/3O3-PbTiO3 (PMN-PT) ceramics are high-performance piezoelectric materials that are widely used in many electronic devices. However, it is extremely difficult to manufacture thin piezoelectric components dozens of micrometers in size using commercial coarse-grained PMN-PT ceramics. This limits the application of PMN-PT ceramics to high-frequency ultrasonic devices. In this work, we prepared a dense, fine-grained PMN-PT ceramic at low temperature using a hot-press sintering (HPS) method. The HPS ceramic had small grains with an average size of 1 μm and maintained high performance with a large permittivity (εr = 4500), piezoelectricity (d33 = 650 pC/N), and electrostrain (SE = 0.14% at 20 kV/cm). The large volume fraction of grain boundaries led to stronger relaxor behavior of the fine-grained PMN-PT ceramic than of the normal coarse-grained one. Owing to its small grains and high piezoelectric performance, this fine-grained PMN-PT ceramic meets the strict requirements of manufacturing thin piezoelectric components. Our results demonstrate that PMN-PT ceramics have great potential for developing low-cost, high-frequency ultrasonic devices by replacing expensive piezoelectric single crystals.

Progress on the Design and Fabrication of High Performance Piezoelectric Flexible Materials Based on Polyvinylidene Fluoride

Progress on the Design and Fabrication of High Performance Piezoelectric Flexible Materials Based on Polyvinylidene Fluoride

Polarization Rotation at Morphotropic Phase Boundary in New Lead-Free Na1/2Bi1/2V1-xTixO3 Piezoceramics.

In this work, we show that polarization rotation enhances the piezoresponse in a high-performance lead-free piezoelectric material, Na1/2Bi1/2V1-xTixO3, a solid solution between tetragonal Na1/2Bi1/2VO3 and rhombohedral Na1/2Bi1/2TiO3, obtained by high-pressure synthesis. The system forms a pure perovskite structure with a favorable morphotropic phase boundary (MPB) located around x = 0.90, which separates the tetragonal and rhombohedral phases. In addition, a distinct monoclinic phase with polarization rotation as functions of composition and temperature is observed. XRD measurements revealed the moderately high Curie temperature of 523 K at x = 0.95 in the MPB. The piezoelectric coefficient d33 of the monoclinic x = 0.95 sample, 42 pC/N, is higher than those of the tetragonal and rhombohedral phases. Even though the present lead-free Na1/2Bi1/2V1-xTixO3 ceramics feature smaller d33 values compared to many currently available lead-free piezoelectric materials as a result of insufficient poling and low density, we expect our findings open up opportunities for exploring promising lead-free piezoelectric materials in Na1/2Bi1/2VO3-based perovskites.

Coexistence of multiple morphotropic phase boundaries in strained La-doped BiFeO3 thin films

The coexistence of two phases across a morphotropic phase boundary (MPB), in piezoelectric materials, usually possess high electromechanical coupling response owing to the electrically controllable of transition between the two phases. Conventionally, morphotropic phase boundary is compositionally driven such as in PbZrO3–PbTiO3 system. Recent study has demonstrated it can be strain-induced in BiFeO3 as well. Using a combination of strain engineering in conjunction with chemical doping, we reveal the coexistence of multiple morphotropic phase boundaries (multi-MPBs) in highly strained BiFeO3 thin films through La doping. By applying an electric field, we show the reversible switching of these multi-MPBs. The discovery of these multi-MPBs in La-doped BiFeO3 thin films further enhance the electromechanical coupling response comparing with the previous observed MPB in pure BiFeO3, opening a new field to obtain high-performance piezoelectric materials.

Coupling selective laser sintering and supercritical CO2 foaming for 3D printed porous polyvinylidene fluoride with improved piezoelectric performance.

In this study, a facile strategy coupling selective laser sintering (SLS) and supercritical carbon dioxide (ScCO2) foaming technology is proposed to prepare a three-dimensional porous polyvinylidene fluoride (PVDF) with an improved piezoelectric output. The effects of foaming conditions including temperature and pressure on foam morphology, crystallization behavior and piezoelectric properties have been systematically studied. It is found that indeed the mechanical stretching foaming process greatly improves the produced content up to 76.2% of the β-phase in PVDF. The piezoelectric output of the PVDF foam with the highest open-circuit voltage could go up to 8 V (4.5 times printed parts), which could light up 4 LED lights and charge 4.7 μF 50 V capacitor to 3.51 V in 275 s. This study provides a feasible approach to 3D porous material fabrication for achieving high-performance piezoelectric materials and demonstrates the promising potential of energy harvesters and smart sensors.

Deterministic contribution of low symmetry phases to piezoresponse in oxide ferroelectrics

Giant piezoelectricity has been thought to be originated from polarization rotation, electric-field-induced phase transformation or nano-domain reorientation in diverse complicated morphotropic phase boundaries (MPB) based piezoelectric ceramics. However, the deterministic contribution to the peak piezoelectricity is still elusive. Here, a full stage of piezoelectric response is presented in pure PbTiO3 films epitaxially constrained as the monoclinic phase on SrTiO3(111), where the as-prepared films feature complicated monoclinic nano-domains with {201} domain boundaries. By applying external voltage, the piezoelectric response undergoes three distinct stages which correspond, respectively, to the three existing mechanisms in terms of polarization rotation, nano-domain reorientation, and electric-field-induced phase transformation. A direct correlation between the electric-poling process and the piezoelectric response is established, confirming that the phase transformation from the monoclinic to tetragonal plays a dominant role for the superior piezoelectric properties of the oxide. This study clarifies the role of monoclinic phase by integrating the three individual mechanisms of piezoresponse into a single-phase perovskite oxide, which may facilitate the development of high-performance piezoelectric materials for electronic device applications.

Enhanced Bipolar Strain and Electrocaloric Response in Gadolinium/Tantalum Co-Substituted Sodium Bismuth Titanate Lead-Free Ceramics

High performance piezoelectric materials with an ABO3 perovskite structure have received growing attention in recent research due to their technological applications in sophisticated research, medical and defence devices like piezoelectric sensors, transducers, ultrasonic motors, nano-positioners, actuators and imaging devices, etc. The technical utility of these materials stems from the various possibilities they offer for cation substitution in the A (or) B sites, which provide valuable opportunities for the optimization and tailoring of desired properties. To date, lead based perovskites, such as lead zirconate titanate (PZT), PZN-PT, and PMN-PT materials, have been extensively investigated in the literature. Although lead based materials exhibit highest piezoelectric coefficients, their wide-scale application has often been hampered by considering the toxicity of lead and its effect on environment and health. This triggered the search for alternative materials that could replace the lead-based ceramics and results in less-hazardous production methods, use and recycling. This has led to a continuous search of potentially attractive alternative lead-free ceramic materials to their counterpart lead based materials for specific applications. Among various kinds of lead-free piezoelectric materials, Na0.5Bi0.5TiO3 (NBT)-based materials are considered to be promising candidates for replacing the lead-based materials. They have been extensively investigated by the condensed materials physics community because of their complicate phase transitions and superior piezo-response. Compared to various chemical substitutions, tantalum (Ta) substitution provides superior electro-strain for the NBT- based ferroelectrics, while the effect of tantalum oxide additive was rarely reported. Gd3+ and Ta5+ co-substituted (Na0.5Bi0.497Gd0.003)Ti1-xTaxO3 (NBGT-Tax) lead-free piezoelectric ceramics are synthesized by using hydrothermal technique. The influence of Ta5+ substitution on the sintering, microstructure, phase transition, and various electrical properties of NBGT ceramics was investigated. Tantalum substitution has no remarkable effect on the microstructure and densification within the studied doping composition. The X-ray diffraction studies revealed that both NBGT-Tax (x=0.000) and NBGT-Tax (x=0.003) ceramics exhibited single phases monoclinic crystal structure with Cc phase. However, with substitution of tantalum the antiferroelectric phase zone gets broader. Simultaneously, the temperature for a ferroelectric to antiferroelectric phase transition is reduced along with an increase in temperature for a transition from antiferroelectric phases to paraelectric phases. This results indicate that tantalum occupies B site of the perovskite structure behaving as a donor, producing A-site cation vacancies. The undoped NBGT ceramics shows good ferroelectric and piezoelectric properties (remnant polarization Pr = 34.2 μC/cm2). The value of remnant polarization was found to increase with Ta substitution along with an increase in coercive field as shown in the figure attached. This is because of the ferroelectric properties being influenced by composition and its homogeneity, defects, external field and orientation of domains, which eventually contributed to the materials response. Meanwhile, the addition of Ta leads to an increase in the electro-strain, together with a higher normalized strain. Moreover, the materials with temperature dependent polarization can be used for solid state cooling applications. The NBGT-Tax compositions shows decrement in the remnant polarization with the increasing temperature which causes increment in the change in entropy. Consequently, the material exhibits the conventional electrocaloric effect (ECE). This simultaneous presence of large field-induced bipolar strain and ECE response along with isothermal change in entropy opens window for great potential applications in the field of electronic devices. Figure 1

Intrinsic piezoelectricity in (K,Na)NbO3-based lead-free single crystal: Piezoelectric anisotropy and its evolution with temperature

Searching for lead-free piezoelectric materials with a large piezoelectricity and excellent thermal stability has been a major concern in both scientific research and practical applications. To understand the mechanism of high piezoelectricity and its temperature-dependent behavior in lead-free materials, we focus here on the tetragonal (K,Na,Li)(Nb,Ta)O3 single crystal and investigate the intrinsic d33* along arbitrary directions as well as its evolution with temperature. The synergistic influence of several factors (narrow tetragonal temperature interval, sharp tetragonal-cubic phase transition, and large PS below TC) leads to a strong anisotropy in the d33* profile, while a high d33* is obtained around θ = 45° over a wide temperature range. This work comprehensively reveals the physical mechanism of piezoelectric anisotropy in lead-free materials, which provides vital information to design high-performance lead-free piezoelectric materials through orientation engineering and lattice manipulation, which is expected to benefit a wide range of piezoelectric materials.

Giant piezoelectricity in oxide thin films with nanopillar structure.

High-performance piezoelectric materials are critical components for electromechanical sensors and actuators. For more than 60 years, the main strategy for obtaining large piezoelectric response has been to construct multiphase boundaries, where nanoscale domains with local structural and polar heterogeneity are formed, by tuning complex chemical compositions. We used a different strategy to emulate such local heterogeneity by forming nanopillar regions in perovskite oxide thin films. We obtained a giant effective piezoelectric coefficient [Formula: see text] of ~1098 picometers per volt with a high Curie temperature of ~450°C. Our lead-free composition of sodium-deficient sodium niobate contains only three elements (Na, Nb, and O). The formation of local heterogeneity with nanopillars in the perovskite structure could be the basis for a general approach to designing and optimizing various 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.

Improvement of the electroactiveβ-phase nucleation and piezoelectric properties of PVDF-HFP thin films influenced by TiO2 nanoparticles

A piezoelectric nanocomposite film is designed to convert daily human activities and acoustic vibrations into usable electrical energy. The nanoparticles (NPs) of titanium dioxide (TiO2) act as a nucleating agent within the PVDF-HFP matrix, which improves the overall performance of the piezoelectric nanocomposite film. They have effectively improved the piezoelectric properties of the β phase of the PVDF-HFP nanocomposite films. In this work, a high-performance piezoelectric material is presented which can be used as an autonomous system. Titanium dioxide nanoparticles (TiO2 NPs)/PVDF-HFP composites were prepared by solution casting method in Dimethyl Acetamide (DMAc) solvent with various contents of TiO2. The compatibility between the PVDF-HFP matrix and TiO2 nanoparticles results in the formation of purely piezoelectric β-polymorph at 1 wt% of TiO2 content. Bellow that content a mixture of β and α-polymorph is observed. The as-obtained flexible nanocomposite films with such TiO2 nanoparticles content can be used as active materials in the field of piezoelectric applications. The crystallinity phases of the PVDF-HFP thin film composites and the β-polymorph formation were characterized by Fourier transform infrared spectroscopy.

Ultrahigh field-induced strain in lead-free ceramics

Abstract Due to the worldwide concerns of environmental protection and sustainable development, lead-free piezoelectric materials are greatly desired for bridging the electrical energy to the mechanical energy. However, their lower energy conversion coefficient compared to the conventional lead-containing piezoelectric materials significantly limits their device applications. Herein, we introduce a novel strategy to increase the strain of lead-free ferroelectric system via material structure design to create polar nano regions (PNRs) and point defects in the material while retaining the global ferroelectric phase. This added short-range structural heterogeneity in the material will facilitate the field-induced phase transition and reversible domain wall switching to enhance the strain. Following this strategy, we demonstrate an ultrahigh strain induced by an electric field in non-textured lead-free Bi0.5Na0.5TiO3 (BNT)-based ceramics. The strain in unipolar mode (Suni) can reach up to 0.74% at 70 kV/cm, making it the highest value in reported lead-free ceramics so far. This puts forward a good route to design high-performance piezoelectric materials by material structure engineering. It also reveals the promising potential of lead-free piezoelectric materials in practical electromechanical device applications.