Showing papers on "Piezoelectricity published in 2013"

Diisopropylammonium Bromide Is a High-Temperature Molecular Ferroelectric Crystal

Abstract: Molecular ferroelectrics are highly desirable for their easy and environmentally friendly processing, light weight, and mechanical flexibility. We found that diisopropylammonium bromide (DIPAB), a molecular crystal processed from aqueous solution, is a ferroelectric with a spontaneous polarization of 23 microcoulombs per square centimeter [close to that of barium titanate (BTO)], high Curie temperature of 426 kelvin (above that of BTO), large dielectric constant, and low dielectric loss. DIPAB exhibits good piezoelectric response and well-defined ferroelectric domains. These attributes make it a molecular alternative to perovskite ferroelectrics and ferroelectric polymers in sensing, actuation, data storage, electro-optics, and molecular or flexible electronics.

Temperature-Insensitive (K,Na)NbO3-Based Lead-Free Piezoactuator Ceramics

Abstract: The development of lead-free piezoceramics has attracted great interest because of growing environmental concerns. A polymorphic phase transition (PPT) has been utilized in the past to tailor piezoelectric properties in lead-free (K,Na)NbO3 (KNN)-based materials accepting the drawback of large temperature sensitivity. Here a material concept is reported, which yields an average piezoelectric coefficientd33 of about 300 pC/N and a high level of unipolar strain up to 0.16% at room temperature. Most intriguingly, field-induced strain varies less than 10% from room temperature to 175 °C. The temperature insensitivity of field-induced strain is rationalized using an electrostrictive coupling to polarization amplitude while the temperature-dependent piezoelectric coefficient is discussed using localized piezoresponse probed by piezoforce microscopy. This discovery opens a new development window for temperature-insensitive piezoelectric actuators despite the presence of a polymorphic phase transition around room temperature.

High-Temperature Piezoelectric Sensing

Abstract: Piezoelectric sensing is of increasing interest for high-temperature applications in aerospace, automotive, power plants and material processing due to its low cost, compact sensor size and simple signal conditioning, in comparison with other high-temperature sensing techniques. This paper presented an overview of high-temperature piezoelectric sensing techniques. Firstly, different types of high-temperature piezoelectric single crystals, electrode materials, and their pros and cons are discussed. Secondly, recent work on high-temperature piezoelectric sensors including accelerometer, surface acoustic wave sensor, ultrasound transducer, acoustic emission sensor, gas sensor, and pressure sensor for temperatures up to 1,250 °C were reviewed. Finally, discussions of existing challenges and future work for high-temperature piezoelectric sensing are presented.

Flexible Piezoelectric PMN–PT Nanowire-Based Nanocomposite and Device

Abstract: Piezoelectric nanocomposites represent a unique class of materials that synergize the advantageous features of polymers and piezoelectric nanostructures and have attracted extensive attention for the applications of energy harvesting and self-powered sensing recently Currently, most of the piezoelectric nanocomposites were synthesized using piezoelectric nanostructures with relatively low piezoelectric constants, resulting in lower output currents and lower output voltages Here, we report a synthesis of piezoelectric (1 - x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-PT) nanowire-based nanocomposite with significantly improved performances for energy harvesting and self-powered sensing With the high piezoelectric constant (d33) and the unique hierarchical structure of the PMN-PT nanowires, the PMN-PT nanowire-based nanocomposite demonstrated an output voltage up to 78 V and an output current up to 229 μA (current density of 458 μA/cm(2)); this output voltage is more than double that of other reported piezoelectric nanocomposites, and the output current is at least 6 times greater The PMN-PT nanowire-based nanocomposite also showed a linear relationship of output voltage versus strain with a high sensitivity The enhanced performance and the flexibility of the PMN-PT nanowire-based nanocomposite make it a promising building block for energy harvesting and self-powered sensing applications

r-Shaped hybrid nanogenerator with enhanced piezoelectricity.

Abstract: Piezoelectric and triboelectric nanogenerators (NGs) have been proposed in the past few years to effectively harvest mechanical energy from the environment. Here, a polydimethylsiloxane (PDMS) layer is placed under the aluminum electrode of polyvinylidene fluoride (PVDF), thus forming an r-shaped hybrid NG. Micro/nanostructures have been fabricated on the PDMS surface and the aluminum electrodes of PVDF to enhance the output performance. Power densities of the piezoelectric part and the triboelectric part are 10.95 and 2.04 mW/cm(3), respectively. Moreover, influence of the triboelectric charges on the piezoelectric output voltage is investigated. Both finite element method simulations and experimental measurements are conducted to verify this phenomenon. The novel hybrid NG is also demonstrated as a power source for consumer electronics. Through one cycle of electric generation, 10 light-emitting diodes are lighted up instantaneously, and a 4-bit liquid crystal display can display continuously for more than 15 s. Besides, the device is integrated into a keyboard to harvest energy in the typing process.

Flexible and Large-Area Nanocomposite Generators Based on Lead Zirconate Titanate Particles and Carbon Nanotubes

Abstract: 25 ] provides a new concept and simple fabrication approach for low-cost self-powered energy systems. However, there are still the unresolved issues with fl exible piezoelectric nanogenerators, such as insuffi cient output performance and size limitations before they can be commercialized for oper-ating sensor network systems. Here, we demonstrate a large-area and highly effi cient NCG device using a bar-coating technique with inherently excellent piezoelectric PZT particles to signifi cantly increase electric output performance. Due to the exceptional piezoelectric per-formance compared to other piezoelectric materials, PZT-based piezoelectric devices have been widely commercialized for not only energy harvesting devices

Piezoelectric properties of PVDF/MWCNT nanofiber using near-field electrospinning

Abstract: This study reports the use of near-field electrospinning to fabricate polyvinylidene fluoride (PVDF) piezoelectric nanofibers mixed with multiwalled-carbon nanotubes (MWCNT). This study also investigates the mechanical strength and piezoelectric characteristics of a single PVDF/MWCNT nanofiber. The morphology and polarization intensity of piezoelectric fiber can be controlled by adjusting the traveling velocity of the X – Y stage, the DC voltage, and the gap between the needle and collection plate. The optimal parameters of the PVDF solution, such as the PVDF powder weight percentage and MWCNT content, were also determined. X-ray diffraction (XRD) analysis shows a high diffraction peak at 2 θ = 20.8° in the piezoelectric crystal β-phase structure. ANSYS finite element analysis (FEA) software with coupled field analysis was used to realize piezoelectric actuation behavior of the PVDF fibers. A nano-indentation test (NanoIndenter XP System, MTS co.) was used to investigate Young's modulus of the PVDF fiber. Finally, the fixed–fixed beam structures of PVDF composite fibers were tested using a DC voltage supply. Comparing the polarized fiber with non-polarized fibers, the measurement of the center displacements as a function of electric field was conducted and characterized.

Fundamental formulations and recent achievements in piezoelectric nano-structures: a review

Abstract: Piezoelectric nano-structures have been regarded as the next-generation piezoelectric material due to their inherent nano-sized piezoelectricity. This review summarizes the recent theoretical and experimental findings in piezoelectric nano-structures, including piezoelectric nanowires, nanoplates, nanobeams, nanofilms, nanoparticles, and piezoelectric heterogeneous materials containing piezoelectric nano-inhomogeneities. To begin, the types of piezoelectric nano-structured materials and the wide application of piezoelectric nano-structures in recent years are delineated. Next, the theoretical foundations including the definition of surface stress and electric displacement, the surface constitutive relations, the surface equilibrium equations, and nonlocal piezoelectricity, and their applications, are illustrated. Then, the effective mechanical and piezoelectric properties are depicted. Furthermore, the experimental investigations are classified, and some important observations are discussed. Finally, the perspectives and challenges for the future development of piezoelectric nano-structures are pointed out.

Electromechanical impedance of piezoelectric transducers for monitoring metallic and non-metallic structures: A review of wired, wireless and energy-harvesting methods

Abstract: Electromechanical impedance–based structural health monitoring method had attracted several researchers in the recent past for aerospace, civil, mechanical, timber and biological structures. Smart materials such as piezoelectric (lead zirconate titanate) and macro fibre composite transducers are either surface bonded or embedded inside the host structure to be monitored. These smart materials with an applied input sinusoidal voltage interact with the structure, to sense, measure, process and detect any change in the selected variables (stress, damage) at critical locations. These can be categorized as wire-based ‘advanced non-destructive testing’, wireless-based ‘battery-powered lead zirconate titanate/macro fibre composite’ and energy harvesting–based ‘self-powered lead zirconate titanate/macro fibre composite’ methods. Most importantly, the effectiveness of these electromechanical impedance–methods can be classified into active and passive based on the properties of the material, the component and the s...

Phase Transition Behavior and Large Piezoelectricity Near the Morphotropic Phase Boundary of Lead‐Free (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 Ceramics

Abstract: The phase transition behavior and piezoelectric properties of (Ba1−xCax)(Zr0.1Ti0.9)O3 and (Ba0.85Ca0.15)(ZryTi1−y)O3 ceramics were investigated in this work to find out the potential factors contributing to large piezoelectricity. It was found that the morphotropic phase boundary (MPB) of (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 ceramics was closely related to the presence of an intermediate phase (considered as orthorhombic phase in this work) between rhombohedral (R) and tetragonal (T) phases at a narrow region, which could be carefully adjusted by the temperature and contents of Ca and Zr in the composition. In addition, the maximum piezoelectric and electromechanical coupling coefficients (with d33 = 572 pC/N and kp = 0.57) were observed near the MPB region close to T phase side, which might be intimately related to the presence of the intermediate phase. This investigation yielded a new sight to understand the mechanism of enhanced piezoelectricity near the MPB.

A new energy harvester design for high power output at low frequencies

Abstract: The energy harvesters (EHs) using resonant mechanism have encountered two major issues: low output power scavenged from low frequency vibrations, and limited effectiveness of harvesting mechanism in a narrow range near resonant frequency. To overcome these issues, we have proposed a piezoelectric EH comprising a composite cantilever and a proof mass at the free end. The composite cantilever is formed by a piezoelectric bimorph and a polymer beam (soft spring) mechanically connected along the longitudinal direction. Comparing with the resonant frequency of 275 Hz of a standalone piezoelectric bimorph, the composite cantilever design enables the resonant frequency of the EH to be as low as 36 Hz. Moreover, this kind of EH is demonstrated to be 3.12 times and 1.32 times (at 0.1 g) more efficient at output power generation than a standalone piezoelectric bimorph and piezoelectric bimorph with a proof mass at the free end, respectively. With the aid of spring hardening effect, the operating bandwidth (BW) can be increased from 5 Hz to 16.4 Hz.

Energy harvesting using a PZT ceramic multilayer stack

Abstract: In this paper, the interdisciplinary energy harvesting issues on piezoelectric energy harvesting were investigated using a ‘33’ mode (mechanical stress and/or electric field are in parallel to the polarization direction) lead zirconate titanate multilayer piezoelectric stack (PZT-Stack). Key energy harvesting characteristics including the generated electrical energy/power in the PZT-Stack, the mechanical to electrical energy conversion efficiency, the power delivered from the PZT-Stack to a resistive load, the electrical charge/energy transferred from the PZT-Stack to a super-capacitor were systematically addressed. Theoretical models for power generation and delivery to a resistive load were proposed and experimentally affirmed. In a quasi-static regime, 70% generated electrical powers were delivered to matched resistive loads. A 35% mechanical to electrical energy conversion efficiency, which is more than 4 times higher than other reports, for the PZT-Stack had been obtained. The generated electrical power and power density were significantly higher than those from a similar weight and size cantilever-type piezoelectric harvester in both resonance and off-resonance modes. In addition, our study indicated that the capacitance and piezoelectric coefficient of the PZT-Stack were strongly dependent on the dynamic stress. (Some figures may appear in colour only in the online journal)

Grain Size Effects on Piezoelectric Properties and Domain Structure of BaTiO3 Ceramics Prepared by Two-Step Sintering

Abstract: A series of highly dense barium titanate (BaTiO3) ceramics with the average grain size (GS) from 0.29 to 8.61 μm are successfully prepared by two-step sintering, and the GS effect on piezoelectric coefficient (d33) is systematically discussed in this work. It is found that when GS above 1 μm, d33 can be enhanced with decreasing GS, reaching a maximum value of 519 pC/N around 1 μm due to the high activity of domain wall mobility. Subsequently, d33 rapidly drops with a further decrease in GS owing to the reduced domain density. The results suggest that it is possible to prepare high-performance BaTiO3 ceramics by controlling the GS and domain configuration properly, which brings great revitalization to the BaTiO3-based piezoceramics.

Bifurcated Polarization Rotation in Bismuth-Based Piezoelectrics

Abstract: ABO3 perovskite-type solid solutions display a large variety of structural and physical properties, which can be tuned by chemical composition or external parameters such as temperature, pressure, strain, electric, or magnetic fields. Some solid solutions show remarkably enhanced physical properties including colossal magnetoresistance or giant piezoelectricity. It has been recognized that structural distortions, competing on the local level, are key to understanding and tuning these remarkable properties, yet, it remains a challenge to experimentally observe such local structural details. Here, from neutron pair-distribution analysis, a temperature-dependent 3D atomic-level model of the lead-free piezoelectric perovskite Na0.5Bi0.5TiO3 (NBT) is reported. The statistical analysis of this model shows how local distortions compete, how this competition develops with temperature, and, in particular, how different polar displacements of Bi3+ cations coexist as a bifurcated polarization, highlighting the interest of Bi-based materials in the search for new lead-free piezoelectrics.

Synthesis mechanism of grain-oriented lead-free piezoelectric Na0.5Bi0.5TiO3–BaTiO3 ceramics with giant piezoelectric response

Abstract: In this paper, we report the synthesis of [001]pc/[012]Rh (pc: pseudo cubic, Rh: rhombohedral) grain oriented lead-free piezoelectric 0.93(Na0.5Bi0.5TiO3)–0.07BaTiO3 (NBT–BT) ceramic with Na0.5Bi0.5TiO3 (NBT) as the seed template. The difference in surface energy along with the chemical potential gradient between the stable NBT seeds and the metastable liquid phase was the driving force for the growth of textured grain. Interfaces in the microstructure were found to be coherent at the atomic scale facilitating the domain wall motion with an applied electric field. The strong texturing in [001]pc/[012]Rh was found to result in extra structural distortions manifested by a decreasing lattice parameter and increasing rhombohedral angle (α). The textured specimen exhibited rather ordered domains with smaller size as compared to its randomly oriented counterpart. The piezoelectric response was found to increase monotonously with the increase in the degree of texturing and the optimized microstructure was found to provide 200% enhancement in the magnitude of piezoelectric coefficient (d33 ∼ 322 pC N−1) as compared to its randomly oriented form (d33 ∼ 160 pC N−1).

Flexoelectric effect on the electroelastic responses of bending piezoelectric nanobeams

Abstract: Flexoelectricity, referring to a spontaneous electric polarization induced by strain gradient in dielectrics, presents a strong size dependency at the nanoscale. In the current work, the influence of the flexoelectric effect on the mechanical and electrical properties of bending piezoelectric nanobeams with different boundary conditions is investigated. Based on the extended linear piezoelectricity theory and the Euler beam model, analytical solutions of the electroelastic fields in the piezoelectric nanobeams subjected to both electrical and mechanical loads are obtained with the inclusion of the flexoelectric effect. Simulation results show that the flexoelectric effect on the elastic behavior of bending beams is sensitive to the beam boundary conditions and the applied electrical load. In addition, for a cantilever piezoelectric nanobeam, an axial relaxation strain is induced from the piezoelectric and flexoelectric effects, while these effects induce a resultant axial force in both the clamped-clamped and simply supported piezoelectric nanobeams. Results also indicate that the flexoelectric effect plays a significant role in the contact stiffness and electric polarization of piezoelectric beams when their thickness is at the nanoscale. It is found that the flexoelectric effect on the electroelastic responses of piezoelectric nanobeams is more pronounced for the beams with smaller thickness. These results are useful for understanding the fundamental mechanical and physical properties of bending piezoelectric nanobeams.

Fundamental Analysis of Piezocatalysis Process on the Surfaces of Strained Piezoelectric Materials

Abstract: Recently, the strain state of a piezoelectric electrode has been found to impact the electrochemical activity taking place between the piezoelectric material and its solution environment. This effect, dubbed piezocatalysis, is prominent in piezoelectric materials because the strain state and electronic state of these materials are strongly coupled. Herein we develop a general theoretical analysis of the piezocatalysis process utilizing well-established piezoelectric, semiconductor, molecular orbital and electrochemistry frameworks. The analysis shows good agreement with experimental results, reproducing the time-dependent voltage drop and H2 production behaviors of an oscillating piezoelectric Pb(Mg1/3Nb2/3)O3-32PbTiO3 (PMN-PT) cantilever in deionized water environment. This study provides general guidance for future experiments utilizing different piezoelectric materials, such as ZnO, BaTiO3, PbTiO3, and PMN-PT. Our analysis indicates a high piezoelectric coupling coefficient and a low electrical conductivity are desired for enabling high electrochemical activity; whereas electrical permittivity must be optimized to balance piezoelectric and capacitive effects.

Size-dependent bending and vibration behaviour of piezoelectric nanobeams due to flexoelectricity

Abstract: Flexoelectricity, representing a spontaneous electric polarization induced by a non-uniform strain field (or strain gradient), is believed to become manifest and be responsible for the size-dependent properties of dielectric materials at the nanoscale. In this paper, the influence of the flexoelectric effect on the static bending and free vibration of a simply supported piezoelectric nanobeam is investigated based on the extended linear piezoelectricity theory and the Timoshenko beam model. The governing equations of the piezoelectric nanobeam with non-homogeneous boundary conditions are obtained from Hamilton's principle. Explicit expressions of the beam deflection and resonant frequency are derived to show the size-dependency of the flexoelectric effect. It is found that the flexoelectricity has a significant effect on the deflection of the bending beam and may reverse the deflection direction under certain loading conditions. Simulation results also indicate that the influence of the flexoelectricity on the vibration behaviour of the piezoelectric nanobeam is more prominent for beams with smaller thickness. Thus, it is suggested that possible frequency tuning of piezoelectric nanobeams by adjusting the applied electrical load should incorporate the flexoelectric effect. The current study can be claimed as helpful for qualitatively characterizing the trend of the flexoelectric effect on the mechanical responses of piezoelectric nanobeams.

Thermal bifurcation buckling of piezoelectric carbon nanotube reinforced composite beams

Abstract: The nonlinear thermal bifurcation buckling behavior of carbon nanotube reinforced composite (CNTRC) beams with surface-bonded piezoelectric layers is studied in this paper. The governing equations of piezoelectric CNTRC beam are obtained based on the Euler-Bernoulli beam theory and von Karman geometric nonlinearity. Two kinds of carbon nanotube-reinforced composite (CNTRC) beams, namely, uniformly distributed (UD) and functionally graded (FG) reinforcements, are considered. The material properties of FG-CNTRC beam are assumed to be graded in the thickness direction. The SWCNTs are assumed aligned, straight and with a uniform layout. Exact solutions are presented to study the thermal buckling behavior of beams made of a symmetric single-walled carbon nanotube reinforced composite with surface-bonded piezoelectric layers. The critical temperature load is obtained for the nonlinear problem. The effects of the applied actuator voltage, temperature, beam geometry, boundary conditions, and volume fractions of carbon nanotubes on the buckling of piezoelectric CNTRC beams are investigated.

Low frequency acoustic energy harvesting using PZT piezoelectric plates in a straight tube resonator

Abstract: A novel and practical acoustic energy harvesting mechanism to harvest traveling sound at low audible frequency is introduced and studied both experimentally and numerically. The acoustic energy harvester in this study contains a quarter-wavelength straight tube resonator with lead zirconate titanate (PZT) piezoelectric cantilever plates placed inside the tube. When the tube resonator is excited by an incident sound at its acoustic resonance frequency, the amplified acoustic pressure inside the tube drives the vibration motions of piezoelectric plates, resulting in the generation of electricity. To increase the total voltage and power, multiple PZT plates were placed inside the tube. The number of PZT plates to maximize the voltage and power is limited due to the interruption of air particle motion by the plates. It has been found to be more beneficial to place the piezoelectric plates in the first half of the tube rather than along the entire tube. With an incident sound pressure level of 100 dB, an output voltage of 5.089 V was measured. The output voltage increases linearly with the incident sound pressure. With an incident sound pressure of 110 dB, an output voltage of 15.689 V and a power of 12.697 mW were obtained. The corresponding areal and volume power densities are 0:635 mW cm 2 and 15:115 W cm 3 , respectively. (Some figures may appear in colour only in the online journal)

Static and free vibration analyses and dynamic control of composite plates integrated with piezoelectric sensors and actuators by the cell-based smoothed discrete shear gap method (CS-FEM-DSG3)

Abstract: The cell-based smoothed discrete shear gap method (CS-FEM-DSG3) using three-node triangular elements was recently proposed to improve the performance of the discrete shear gap method (DSG3) for static and free vibration analyses of isotropic Mindlin plates. In this paper, the CS-FEM-DSG3 is further extended for static and free vibration analyses and dynamic control of composite plates integrated with piezoelectric sensors and actuators. In the piezoelectric composite plates, the electric potential is assumed to be a linear function through the thickness of each piezoelectric sublayer. A displacement and velocity feedback control algorithm is used for active control of the static deflection and the dynamic response of the plates through closed loop control with bonded or embedded distributed piezoelectric sensors and actuators. The accuracy and reliability of the proposed method is verified by comparing its numerical solutions with those of other available numerical results.

Measurements of Piezoelectric Coefficient d33 of Lead Zirconate Titanate Thin Films Using a Mini Force Hammer

Abstract: Lead zirconate titanate (PbZrxTi1-xO3, or PZT) is a piezoelectric material widely used as sensors and actuators. For microactuators, PZT often appears in the form of thin films to maintain proper aspect ratios. One major challenge encountered is accurate measurement of piezoelectric coefficients of PZT thin films. In this paper, we present a simple, low-cost, and effective method to measure piezoelectric coefficient d33 of PZT thin films through use of basic principles in mechanics of vibration. A small impact hammer with a tiny tip acts perpendicularly to the PZT thin-film surface to generate an impulsive force. In the meantime, a load cell at the hammer tip measures the impulsive force and a charge amplifier measures the responding charge of the PZT thin film. Then the piezoelectric coefficient d33 is obtained from the measured force and charge based on piezoelectricity and a finite element modeling. We also conduct a thorough parametric study to understand the sensitivity of this method on various parameters, such as substrate material, boundary conditions, specimen size, specimen thickness, thickness ratio, and PZT thin-film material. Two rounds of experiments are conducted to demonstrate the feasibility and accuracy of this new method. The first experiment is to measure d33 of a PZT disk resonator whose d33 is known. Experimental results show that d33 measured via this method is as accurate as that from the manufacturer's specifications within its tolerance. The second experiment is to measure d33 of PZT thin films deposited on silicon substrates. With the measured d33, we predict the displacement of PZT thin-film membrane microactuators. In the meantime, the actuator displacement is measured via a laser Doppler vibrometer. The predicted and measured displacements agree very well validating the accuracy of this new method.

Contribution of piezoelectric effect, electrostriction and ferroelectric/ferroelastic switching to strain-electric field response of dielectrics

Abstract: This paper presents a thorough study of the strain response of different types of electroceramics during dynamical electrical loading. It highlights important aspects to take into account in the experimental methodology and outlines general guidelines for the discussion and interpretation of the results. The contributions of piezoelectric effect, electrostriction and ferroelectric/ferroelastic domain switching to the strain produced during the application of an alternating electric field are discussed by describing the strain-electric field (S-E) loops of different dielectric ceramics in which each of these contributions are predominant. In particular, attention is given to the description of the strain evolution in the characteristic "butterfly loops" typically shown by ferroelectric materials. The strain-polarization loop is indicated as a useful means to reveal the interconnection between strain and polarization state during dynamical electrical loading. Strain rate is suggested as a powerful tool to obtain more detailed information regarding the mechanisms of the electric field-induced strain.

Large size lead-free (Na,K)(Nb,Ta)O3 piezoelectric single crystal: growth and full tensor properties

Abstract: Environmental friendly piezoelectric single crystal, Ta-modified (K,Na)NbO3 with the size of 12 × 11 × 11 mm3, has been successfully grown using the top seeded solution growth technique. This orthorhombic phase (K,Na)(Nb,Ta)O3 single crystal is the largest size to date in KNN-based crystals with homogeneous composition. The large size allowed us to apply the domain engineering technique to further enhance its piezoelectric properties. In addition, a self-consistent complete set of elastic, dielectric and piezoelectric constants for the [001]c poled domain engineered crystal has been measured, which is urgently needed for theoretical studies and simulation designs of electromechanical devices using this lead-free piezoelectric material. The electromechanical coupling factors are very high (k33 = 0.827, kt = 0.646) and the dielectric loss tangent is as low as 0.004 for this lead-free piezoelectric crystal. Such excellent properties make this crystal an excellent candidate to replace lead-containing piezoelectric materials in electromechanical devices.

Effect of poling time and grid voltage on phase transition and piezoelectricity of poly(vinyledene fluoride) thin films using corona poling

Abstract: Corona poling was used to create piezoelectric polyvinylidene flouride (PVDF) thin films and the effects of poling time and grid voltage on the electric and physical properties of the samples was studied. Using x-ray diffraction, infrared spectroscopy, and direct measurement of piezoelectricity, the phase transition behaviour and piezoelectric constant of stretched and poled PVDF film was investigated. Results indicate that the poling time and grid voltage have no substantial influence on the phase transition behaviour of PVDF. However, they were found to have a significant effect on the piezoelectric charge constant of PVDF.

Size-dependent piezoelectricity and elasticity due to the electric field-strain gradient coupling and strain gradient elasticity

Abstract: A size-dependent nonclassical Bernoulli–Euler beam model based on the strain gradient elasticity is proposed for piezoelectric nanowires. The governing equations and the corresponding boundary conditions are naturally derived from the variational principle. Different from the classical piezoelectric beam theory, the electric field–strain gradient coupling and the strain gradient elasticity are both taken into account. Static bending problem of a cantilever piezoelectric nanobeam is solved to illustrate the effect of strain gradient. The present model contains material length scale parameters and can capture the size dependent piezoelectricity and elasticity for nanoscale piezoelectric structures. The numerical results reveal that the deflections predicted by the present model are smaller than that by the classical beam theory and the effective electromechanical coupling coefficient is dramatic enhanced by the electric field–strain gradient coupling effect. However, the differences in both the deflections and effective EMC coefficient between the two models are very significant when the beam thickness is very small; they are diminishing with the increase of the beam thickness. This model is helpful for understanding the electromechanically coupling mechanism and in designing piezoelectric nanowires based devices.

Giant energy density in [001]-textured Pb(Mg1/3Nb2/3)O3-PbZrO3-PbTiO3 piezoelectric ceramics

Abstract: Pb(Zr,Ti)O3 (PZT) based compositions have been challenging to texture or grow in a single crystal form due to the incongruent melting point of ZrO2. Here we demonstrate the method for achieving 90% textured PZT-based ceramics and further show that it can provide highest known energy density in piezoelectric materials through enhancement of piezoelectric charge and voltage coefficients (d and g). Our method provides more than ∼5× increase in the ratio d(textured)/d(random). A giant magnitude of d·g coefficient with value of 59 000 × 10−15 m2 N−1 (comparable to that of the single crystal counterpart and 359% higher than that of the best commercial compositions) was obtained.