Showing papers on "Piezoelectricity published in 2011"

Piezoelectric Energy Harvesting

Abstract: About the Authors. Preface. 1. Introduction to Piezoelectric Energy Harvesting. 1.1 Vibration-Based Energy Harvesting Using Piezoelectric Transduction. 1.2 An Examples of a Piezoelectric Energy Harvesting System. 1.3 Mathematical Modeling of Piezoelectric Energy Harvesters. 1.4 Summary of the Theory of Linear Piezoelectricity. 1.5 Outline of the Book. 2. Base Excitation Problem for Cantilevered Structures and Correction of the Lumped-Parameter Electromechanical Model. 2.1 Base Excitation Problem for the Transverse Vibrations. 2.2 Correction of the Lumped-Parameter Base Excitation Model for Transverse Vibrations. 2.3 Experimental Case Studies for Validation of the Correction Factor. 2.4 Base Excitation Problem for Longitudinal Vibrations and Correction of its Lumped-Parameter Model. 2.5 Correction Factor in the Electromechanically Coupled Lumped-Parameter Equations and a Theoretical Case Study. 2.6 Summary. 2.7 Chapter Notes. 3. Analytical Distributed-Parameter Electromechanical Modeling of Cantilevered Piezoelectric Energy Harvesters. 3.1 Fundamentals of the Electromechanically Coupled Distributed-Parameter Model. 3.2 Series Connection of the Piezoceramic Layers. 3.3 Parallel Connection of Piezoceramic Layers. 3.4 Equivalent Representation of the Series and the Parallel Connection Cases. 3.5 Single-Mode Electromechanical Equations for Modal Excitations. 3.6 Multi-mode and Single-Mode Electromechanical FRFs. 3.7 Theoretical Case Study. 3.8 Summary. 3.9 Chapter Notes. 4. Experimental Validation of the Analytical Solution for Bimorph Configurations. 4.1 PZT-5H Bimorph Cantilever without a Tip Mass. 4.2 PZT-5H Bimorph Cantilever with a Tip Mass. 4.3 PZT-5A Bimorph Cantilever. 4.4 Summary. 4.5 Chapter Notes. 5. Dimensionless Equations, Asymptotic Analyses, and Closed-Form Relations for Parameter Identification and Optimization. 5.1 Dimensionless Representation of the Single-Mode Electromechanical FRFs. 5.2 Asymptotic Analyses and Resonance Frequencies. 5.3 Identification of Mechanical Damping. 5.4 Identification of the Optimum Electrical Load for Resonance Excitation. 5.5 Intersection of the Voltage Asymptotes and a Simple Technique for the Experimental Identification of the Optimum Load Resistance. 5.6 Vibration Attenuation Amplification from the Short-Circuit to Open-Circuit Conditions. 5.7 Experimental Validation for a PZT-5H Bimorph Cantilever. 5.8 Summary. 5.9 Chapter Notes. 6. Approximate Analytical Distributed-Parameter Electromechanical Modeling of Cantilevered Piezoelectric Energy Harvesters. 6.1 Unimorph Piezoelectric Energy Harvester Configuration. 6.2 Electromechanical Euler-Bernoulli Model with Axial Deformations. 6.3 Electromechanical Rayleigh Model with Axial Deformations. 6.4 Electromechanical Timoshenko Model with Axial Deformations. 6.5 Modeling of Symmetric Configurations. 6.6 Presence of a Tip Mass in the Euler-Bernoulli, Rayleigh, and Timoshenko Models. 6.7 Comments on the Kinematically Admissible Trial Functions. 6.8 Experimental Validation of the Assumed-Modes Solution for a Bimorph Cantilever. 6.9 Experimental Validation for a Two-Segment Cantilever. 6.10 Summary. 6.11 Chapter Notes. 7. Modeling of Piezoelectric Energy Harvesting for Various Forms of Dynamic Loading. 7.1 Governing Electromechanical Equations. 7.2 Periodic Excitation. 7.3 White Noise Excitation. 7.4 Excitation Due to Moving Loads. 7.5 Local Strain Fluctuations on Large Structures. 7.6 Numerical Solution for General Transient Excitation. 7.7 Case Studies. 7.8 Summary. 7.9 Chapter Notes. 8. Modeling and Exploiting Mechanical Nonlinearities in Piezoelectric Energy Harvesting. 8.1 Perturbation Solution of the Piezoelectric Energy Harvesting Problem: the Method of Multiple Scales. 8.2 Monostable Duffing Oscillator with Piezoelectric Coupling. 8.3 Bistable Duffing Oscillator with Piezoelectric Coupling: the Piezomagnetoelastic Energy Harvester. 8.4 Experimental Performance Results of the Bistable Peizomagnetoelastic Energy Harvester. 8.5 A Bistable Plate for Piezoelectric Energy Harvesting. 8.6 Summary. 8.7 Chapter Notes. 9. Piezoelectric Energy Harvesting from Aeroelastic Vibrations. 9.1 A Lumped-Parameter Piezoaeroelastic Energy Harvester Model for Harmonic Response. 9.2 Experimental Validations of the Lumped-Parameter Model at the Flutter Boundary. 9.3 Utilization of System Nonlinearities in Piezoaeroelastic Energy Harvesting. 9.4 A Distributed-Parameter Piezoaeroelastic Model for Harmonic Response: Assumed-Modes Formulation. 9.5 Time-Domain and Frequency-Domain Piezoaeroelastic Formulations with Finite-Element Modeling. 9.6 Theoretical Case Study for Airflow Excitation of a Cantilevered Plate. 9.7 Summary. 9.8 Chapter Notes. 10. Effects of Material Constants and Mechanical Damping on Power Generation. 10.1 Effective Parameters of Various Soft Ceramics and Single Crystals. 10.2 Theoretical Case Study for Performance Comparison of Soft Ceramics and Single Crystals. 10.3 Effective Parameters of Typical Soft and Hard Ceramics and Single Crystals. 10.4 Theoretical Case Study for Performance Comparison of Soft and Hard Ceramics and Single Crystals. 10.5 Experimental Demonstration for PZT-5A and PZT-5H Cantilevers. 10.6 Summary. 10.7 Chapter Notes. 11. A Brief Review of the Literature of Piezoelectric Energy Harvesting Circuits. 11.1 AC-DC Rectification and Analysis of the Rectified Output. 11.2 Two-Stage Energy Harvesting Circuits: DC-DC Conversion for Impedance Matching. 11.3 Synchronized Switching on Inductor for Piezoelectric Energy Harvesting. 11.4 Summary. 11.5 Chapter Notes. Appendix A. Piezoelectric Constitutive Equations. Appendix B. Modeling of the Excitation Force in Support Motion Problems of Beams and Bars. Appendix C. Modal Analysis of a Uniform Cantilever with a Tip Mass. Appendix D. Strain Nodes of a Uniform Thin Beam for Cantilevered and Other Boundary Conditions. Appendix E. Numerical Data for PZT-5A and PZT-5H Piezoceramics. Appendix F. Constitutive Equations for an Isotropic Substructure. Appendix G. Essential Boundary Conditions for Cantilevered Beams. Appendix H. Electromechanical Lagrange Equations Based on the Extended Hamilton s Principle. Index.

Piezoelectric Materials for High Temperature Sensors

Abstract: Piezoelectric materials that can function at high temperatures without failure are desired for structural health monitoring and/or nondestructive evaluation of the next generation turbines, more efficient jet engines, steam, and nuclear/electrical power plants. The operational temperature range of smart transducers is limited by the sensing capability of the piezoelectric material at elevated temperatures, increased conductivity and mechanical attenuation, variation of the piezoelectric properties with temperature. This article discusses properties relevant to sensor applications, including piezoelectric materials that are commercially available and those that are under development. Compared to ferroelectric polycrystalline materials, piezoelectric single crystals avoid domain-related aging behavior, while possessing high electrical resistivities and low losses, with excellent thermal property stability. Of particular interest is oxyborate [ReCa4O (BO3)3] single crystals for ultrahigh temperature applications (>1000°C). These crystals offer piezoelectric coefficients deff, and electromechanical coupling factors keff, on the order of 3–16 pC/N and 6%–31%, respectively, significantly higher than those values of α-quartz piezocrystals (~2 pC/N and 8%). Furthermore, the absence of phase transitions prior to their melting points ~1500°C, together with ultrahigh electrical resistivities (>106 Ω·cm at 1000°C) and thermal stability of piezoelectric properties (< 20% variations in the range of room temperature ~1000°C), allow potential operation at extreme temperature and harsh environments.

Flexoelectric rotation of polarization in ferroelectric thin films

Abstract: Strain engineering enables modification of the properties of thin films using the stress from the substrates on which they are grown. Strain may be relaxed, however, and this can also modify the properties thanks to the coupling between strain gradient and polarization known as flexoelectricity. Here we have studied the strain distribution inside epitaxial films of the archetypal ferroelectric PbTiO3, where the mismatch with the substrate is relaxed through the formation of domains (twins). Synchrotron X-ray diffraction and high-resolution scanning transmission electron microscopy reveal an intricate strain distribution, with gradients in both the vertical and, unexpectedly, the horizontal direction. These gradients generate a horizontal flexoelectricity that forces the spontaneous polarization to rotate away from the normal. Polar rotations are a characteristic of compositionally engineered morphotropic phase boundary ferroelectrics with high piezoelectricity; flexoelectricity provides an alternative route for generating such rotations in standard ferroelectrics using purely physical means.

Enhanced Piezoelectricity and Stretchability in Energy Harvesting Devices Fabricated from Buckled PZT Ribbons

Abstract: The development of a method for integrating highly efficient energy conversion materials onto soft, biocompatible substrates could yield breakthroughs in implantable or wearable energy harvesting systems. Of particular interest are devices which can conform to irregular, curved surfaces, and operate in vital environments that may involve both flexing and stretching modes. Previous studies have shown significant advances in the integration of highly efficient piezoelectric nanocrystals on flexible and bendable substrates. Yet, such inorganic nanomaterials are mechanically incompatible with the extreme elasticity of elastomeric substrates. Here, we present a novel strategy for overcoming these limitations, by generating wavy piezoelectric ribbons on silicone rubber. Our results show that the amplitudes in the waves accommodate order-of-magnitude increases in maximum tensile strain without fracture. Further, local probing of the buckled ribbons reveals an enhancement in the piezoelectric effect of up to 70%, thus representing the highest reported piezoelectric response on a stretchable medium. These results allow for the integration of energy conversion devices which operate in stretching mode via reversible deformations in the wavy/buckled ribbons.

Lead-free NaNbO3 nanowires for a high output piezoelectric nanogenerator

Abstract: Perovskite ferroelectric nanowires have rarely been used for the conversion of tiny mechanical vibrations into electricity, in spite of their large piezoelectricity. Here we present a lead-free NaNbO3 nanowire-based piezoelectric device as a high output and cost-effective flexible nanogenerator. The device consists of a NaNbO3 nanowire–poly(dimethylsiloxane) (PDMS) polymer composite and Au/Cr-coated polymer films. High-quality NaNbO3 nanowires can be grown by hydrothermal method at low temperature and can be poled by an electric field at room temperature. The NaNbO3 nanowire–PDMS polymer composite device shows an output voltage of 3.2 V and output current of 72 nA (current density of 16 nA/cm2) under a compressive strain of 0.23%. These results imply that NaNbO3 nanowires should be quite useful for large-scale lead-free piezoelectric nanogenerator applications.

Giant Piezoelectricity on Si for Hyperactive MEMS

Abstract: Microelectromechanical systems (MEMS) incorporating active piezoelectric layers offer integrated actuation, sensing, and transduction. The broad implementation of such active MEMS has long been constrained by the inability to integrate materials with giant piezoelectric response, such as Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT). We synthesized high-quality PMN-PT epitaxial thin films on vicinal (001) Si wafers with the use of an epitaxial (001) SrTiO3 template layer with superior piezoelectric coefficients (e31,f = –27 ± 3 coulombs per square meter) and figures of merit for piezoelectric energy-harvesting systems. We have incorporated these heterostructures into microcantilevers that are actuated with extremely low drive voltage due to thin-film piezoelectric properties that rival bulk PMN-PT single crystals. These epitaxial heterostructures exhibit very large electromechanical coupling for ultrasound medical imaging, microfluidic control, mechanical sensing, and energy harvesting.

Giant piezoelectricity on Si for hyper-active MEMS

Abstract: High-quality piezoelectric thin films are grown and exhibit superior properties for microelectromechanical systems. Microelectromechanical systems (MEMS) incorporating active piezoelectric layers offer integrated actuation, sensing, and transduction. The broad implementation of such active MEMS has long been constrained by the inability to integrate materials with giant piezoelectric response, such as Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT). We synthesized high-quality PMN-PT epitaxial thin films on vicinal (001) Si wafers with the use of an epitaxial (001) SrTiO3 template layer with superior piezoelectric coefficients (e31,f = –27 ± 3 coulombs per square meter) and figures of merit for piezoelectric energy-harvesting systems. We have incorporated these heterostructures into microcantilevers that are actuated with extremely low drive voltage due to thin-film piezoelectric properties that rival bulk PMN-PT single crystals. These epitaxial heterostructures exhibit very large electromechanical coupling for ultrasound medical imaging, microfluidic control, mechanical sensing, and energy harvesting.

Enhancing Light Emission of ZnO Microwire-Based Diodes by Piezo-Phototronic Effect

Abstract: Light emission from semiconductors depends not only on the efficiency of carrier injection and recombination but also extraction efficiency. For ultraviolet emission from high band gap materials such as ZnO, nanowires have higher extraction efficiencies than thin films, but conventional approaches for creating a p–n diode result in low efficiency. We exploited the noncentral symmetric nature of n-type ZnO nanowire/p-type GaN substrate to create a piezoelectric potential within the nanowire by applying stress. Because of the polarization of ions in a crystal that has noncentral symmetry, a piezoelectric potential (piezopotential) is created in the crystal under stress. The piezopotential acts as a “gate” voltage to tune the charge transport and enhance carrier injection, which is called the piezo-phototronic effect. We propose that band modification traps free carriers at the interface region in a channel created by the local piezoelectric charges. The emission intensity and injection current at a fixed ap...

The Antiferroelectric ↔ Ferroelectric Phase Transition in Lead-Containing and Lead-Free Perovskite Ceramics

Abstract: A comprehensive review on the latest development of the antiferroelectric ↔ ferroelectric phase transition is presented. The abrupt volume expansion and sudden development of polarization at the phase transition has been extensively investigated in PbZrO3-based perovskite ceramics. New research developments in these compositions, including the incommensurate domain structure, the auxetic behavior under electric fields in the induced ferroelectric phase, the ferroelastic behavior of the multicell cubic phase, the impact of radial compression, the unexpected electric field-induced ferroelectric-to-antiferroelectric transition, and the phase transition mechanical toughening effect have been summarized. Due to their significance to leadfree piezoelectric ceramics, compounds with antiferroelectric phases, including NaNbO3, AgNbO3, and (Bi1/2Na1/2)TiO3, are also critically reviewed. Focus has been placed on the (Bi1/2Na1/2)TiO3–BaTiO3 solid solution where the electric field-induced ferroelectric phase remains even after the applied field is removed at room temperature. Therefore, the electric field-induced antiferroelectric-to-ferroelectric phase transition is a key to the poling process to develop piezoelectricity in morphotropic phase boundary (MPB) compositions. The competing phase transition and domain switching processes in 0.93 (Bi1/2Na1/2)TiO3–0.07BaTiO3 are directly imaged with nanometer resolution using the unique in situ transmission electron microscopy (TEM) technique.

Origin of piezoelectricity in an electrospun poly(vinylidene fluoride-trifluoroethylene) nanofiber web-based nanogenerator and nano-pressure sensor.

Abstract: A single stage electrospinning process can give rise to preferentially oriented induced dipoles in poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] nanofibers. The piezoelectricity of as-electrospun P(VDF-TrFE) nanofiber webs opens up new possibilities for their use as a flexible nanogenerators and nano-pressure sensors. In this work, the origin of the piezoelectricity has been spotlighted by randomization of the induced dipoles at the Curie temperature and analyzed by polarized FT-IR spectroscopic techniques as well as by detecting the piezoelectric signal from a nano-pressure sensor.

Large field-induced strains in a lead-free piezoelectric material

Abstract: Piezoelectric materials exhibit a mechanical response to electrical inputs, as well as an electrical response to mechanical inputs, which makes them useful in sensors and actuators. Lead-based piezoelectrics demonstrate a large mechanical response, but they also pose a health risk. The ferroelectric BiFeO(3) is an attractive alternative because it is lead-free, and because strain can stabilize BiFeO(3) phases with a structure that resembles a morphotropic phase boundary. Here we report a reversible electric-field-induced strain of over 5% in BiFeO(3) films, together with a characterization of the origins of this effect. In situ transmission electron microscopy coupled with nanoscale electrical and mechanical probing shows that large strains result from moving the boundaries between tetragonal- and rhombohedral-like phases, which changes the phase stability of the mixture. These results demonstrate the potential of BiFeO(3) as a substitute for lead-based materials in future piezoelectric applications.

Origins of Electro-Mechanical Coupling in Polycrystalline Ferroelectrics During Subcoercive Electrical Loading

Abstract: The electromechanical coupling in ferroelectric materials is controlled by several coexisting structural phenomena which can include piezoelectric lattice strain, 180 degrees and non-180 degrees domain wall motion, and interphase boundary motion. The structural mechanisms that contribute to electromechanical coupling have not been readily measured in the past, particularly under the low-to-medium driving electric field amplitudes at which many piezoelectric materials are used. In this feature, results from in situ, high-energy, and time-resolved X-ray diffraction experiments are interpreted together with macroscopic piezoelectric coefficient measurements in order to better understand the contribution of these mechanisms to the electromechanical coupling of polycrystalline ferroelectric materials. The compositions investigated include 2 mol% La-doped PbZr0.60Ti0.40O3, 2 mol% La-doped PbZr0.52Ti0.48O3, 2 mol% La-doped PbZr0.40Ti0.60O3, undoped PbZr0.52Ti0.48O3, and 2 mol% Fe-doped PbZr0.47Ti0.53O3. In all compositions, a strong correlation is found between the field-amplitude-dependence of the macroscopic piezoelectric coefficient and the contribution of non-180 degrees domain wall motion determined from the diffraction data. The results show directly that the Rayleigh-like behavior of d(33) piezoelectric coefficient is predominantly due to a Rayleigh-like behavior of non-180 degrees domain wall motion. Furthermore, after separating contributions from lattice (atomic level) and domain wall motion (nanoscale level) to the measured macroscopic piezoelectric properties, we show that previously ignored intergranular interactions (microscopic level) account for a surprisingly large portion of the electromechanical coupling. These results demonstrate that electromechanical coupling in polycrystalline aggregates is substantially different from that observed in single crystalline materials. The construct of emergence is used to describe how averaged macrolevel phenomena are different from the material response observed in an isolated subcomponent of the material. Consequently, and due to its size-scale complexity, the description of grain-to-grain interactions is presently inaccessible in most ab initio and phenomenological approaches. Results presented here demonstrate the need to account for these interactions in order to completely describe macroscopic electromechanical properties of polycrystalline materials.

Giant piezoelectric size effects in zinc oxide and gallium nitride nanowires. A first principles investigation.

Abstract: Nanowires made of materials with noncentrosymmetric crystal structure are under investigation for their piezoelectric properties and suitability as building blocks for next-generation self-powered nanodevices. In this work, we investigate the size dependence of piezoelectric coefficients in nanowires of two such materials − zinc oxide and gallium nitride. Nanowires, oriented along their polar axis, ranging from 0.6 to 2.4 nm in diameter were modeled quantum mechanically. A giant piezoelectric size effect is identified for both GaN and ZnO nanowires. However, GaN exhibits a larger and more extended size dependence than ZnO. The observed size effect is discussed in the context of charge redistribution near the free surfaces leading to changes in local polarization. The study reveals that local changes in polarization and reduction of unit cell volume with respect to bulk values lead to the observed size effect. These results have strong implication in the field of energy harvesting, as piezoelectric voltage...

Elastic, piezoelectric, and dielectric properties of Ba(Zr0.2Ti0.8)O3- 50(Ba0.7Ca0.3)TiO3 Pb-free ceramic at the morphotropic phase boundary

Abstract: There is an urgent demand for high performance Pb-free piezoelectrics to substitute for the current workhorse, the lead zirconate titanate (PZT) family. Recently, a triple point (also tricritical point) type morphotropic phase boundary (MPB) in Pb-free Ba(Zr0.2Ti0.8)O3-x(Ba0.7Ca0.3)TiO3 system has been reported that shows equally as excellent piezoelectricity as soft PZT at room temperature (Liu and Ren6). In the present study, we measured a full set of elastic, piezoelectric, and dielectric properties for the MPB composition, Ba(Zr0.2Ti0.8)O3-50(Ba0.7Ca0.3)TiO3 (BZT-50BCT), by using a resonance method. The resonant method gives piezoelectric properties d33 = 546 pC/N, g33 = 15.3 × 10−3 Vm/N, electromechanical coupling factor k33 = 65%, and the elastic constant s33E = 19.7 × 10−12 m2/N, c33E = 11.3 × 1010 N/m2, which are close to the properties of soft PZT (PZT-5A). Furthermore, the piezoelectric coefficients (k33, d33), the ferroelectric properties (coercive field, remnant polarization), and the elastic ...

The vibrational and buckling behaviors of piezoelectric nanobeams with surface effects

Abstract: In this work, the influence of surface effects, including residual surface stress, surface elasticity and surface piezoelectricity, on the vibrational and buckling behaviors of piezoelectric nanobeams is investigated by using the Euler-Bernoulli beam theory. The surface effects are incorporated by applying the surface piezoelectricity model and the generalized Young-Laplace equations. The results demonstrate that surface effects play a significant role in predicting these behaviors. It is found that the influence of the residual surface stress and the surface piezoelectricity on the resonant frequencies and the critical electric potential for buckling is more prominent than the surface elasticity. The nanobeam boundary conditions are also found to influence the surface effects on these parameters. This study also shows that the resonant frequencies can be tuned by adjusting the applied electrical load. The present study is envisaged to provide useful insights for the design and applications of piezoelectric-beam-based nanodevices.

An investigation of energy harvesting from renewable sources with PVDF and PZT

Abstract: Piezoelectric materials have been in use for many years; however, with an increasing concern about global warming, piezoelectricity has gained significant importance in research and development for extracting energy from the environment. In this work the voltage responses of ceramic based piezoelectric fibre composite structures (PFCs) and polymer based piezoelectric strips, PVDF (polyvinylidene fluoride), were evaluated when subjected to various wind speeds and water droplets in order to investigate the possibility of energy generation from these two natural renewable energy sources for utilization in low power electronic devices. The effects of material dimensions, drop mass, releasing height of the drops and wind speed on the voltage output were studied and the power was calculated. This work showed that piezoelectric polymer materials can generate higher voltage/power than ceramic based piezoelectric materials and it was proved that producing energy from renewable sources such as rain drops and wind is possible by using piezoelectric polymer materials.

Stretchable ferroelectric nanoribbons with wavy configurations on elastomeric substrates.

Abstract: Applications of ferroelectric ceramics, ranging from components for sensors, memory devices, microelectromechanical systems, and energy convertors, all involve planar and rigid layouts. The brittle nature of such materials and their high-temperature processing requirements limit applications to devices that involve only very small mechanical deformations and narrow classes of substrates. Here, we report a strategy for integrating nanoribbons of one of the most widely used ferroelectric ceramics, lead zirconate titanate, in “wavy” geometries, on soft, elastomeric supports to achieve reversible, linear elastic responses to large strain deformations (i.e., stretchable properties), without any loss in ferroelectric or piezoelectric properties. Theoretical and computational analysis of the mechanics account for these characteristics and also show that the amplitudes of the waves can be continuously tuned with an applied electric field, to achieve a vertical (normal) displacement range that is near 1000 times l...

Surface effects on the electromechanical coupling and bending behaviours of piezoelectric nanowires

Abstract: In this work, surface effects, including surface elasticity, residual surface stress and surface piezoelectricity, are considered to study the electromechanical coupling (EMC) behaviour of piezoelectric nanowires (NWs) with the Euler–Bernoulli beam theory. Using the surface-layer-based model, explicit formula for EMC coefficient is derived. It is clearly observed that this coefficient is size-dependent and can be strongly enhanced when the geometric dimensions of NWs scale down. The static bending of a cantilever piezoelectric NW is also studied. The surface effects are found to significantly influence the stiffness and electric field distribution in the NW. The results indicate that surface effects play a significant role in the EMC and bending behaviours of piezoelectric nanobeam. This work is very helpful for understanding the size-dependent properties of nanostructured piezoelectric materials and improving the performance of the piezoelectric nanobeam-based devices in energy harvesting.

Structural description of the macroscopic piezo- and ferroelectric properties of lead zirconate titanate.

Abstract: An in situ structural description of the origin of the ferroelectric properties as a function of the applied electric field E was obtained by synchrotron x-ray diffraction. A setup was used to average the effects of the preferred orientation induced by the strong piezoelectric strain and solve in situ the crystal structure as a function of the applied electric field. Hence, we were able to describe the microscopic origin of the macroscopic ferro- and piezoelectric properties of the most widely used ferroelectric material, lead zirconate titanate.

Interface Engineering by Piezoelectric Potential in ZnO-Based Photoelectrochemical Anode

Abstract: Through a process of photoelectrochemical (PEC) water splitting, we demonstrated an effective strategy for engineering the barrier height of a heterogeneous semiconductor interface by piezoelectric polarization, known as the piezotronic effect. A consistent enhancement or reduction of photocurrent was observed when tensile or compressive strains were applied to the ZnO anode, respectively. The photocurrent variation is attributed to a changed barrier height at the ZnO/ITO interface, which is a result of the remnant piezoelectric potential across the interface due to a nonideal free charge distribution in the ITO electrode. In our system, ∼1.5 mV barrier height change per 0.1% applied strain was identified, and 0.21% tensile strain yielded a ∼10% improvement of the maximum PEC efficiency. The remnant piezopotential is dictated by the screening length of the materials in contact with piezoelectric component. The difference between this time-independent remnant piezopotential effect and time-dependent piezoelectric effect is also studied in details.

Remarkably Strong Piezoelectricity of Lead-Free (K0.45Na0.55)0.98Li0.02(Nb0.77Ta0.18Sb0.05)O3 Ceramic

Abstract: Various lead-free (KxNa1−x)0.98Li0.02(Nb0.82−yTa0.18Sby)O3 ceramics with x=0.50, y=0.00–0.07 or x=0.40–0.60, y=0.05 were prepared by the conventional solid-state reaction method. Systematic investigation on the microstructures, crystalline structures, and dielectric and piezoelectric properties was carried out. Remarkably strong piezoelectricity has been achieved in (K0.45Na0.55)0.98Li0.02(Nb0.77Ta0.18Sb0.05)O3 ceramic, which shows the excellent piezoelectric properties of d33=413 pC/N, d31=−153 pC/N, kp=0.50, and k33=0.62. It is considered that the observed strong piezoelectricity should be ascribed to several combined decisive factors, such as the phase coexistence due to an orthorhombic–tetragonal polymorphic phase transition near room temperature, the high electronegativity of Sb5+ ions as compared with those of Nb5+ ions and Ta5+ ions, and the relatively ideal microstructure with high density, large average grain size and narrow grain-size distribution.

Critical property in relaxor-PbTiO3 single crystals - Shear piezoelectric response

Abstract: The shear piezoelectric behavior in relaxor-PbTiO3 (PT) single crystals is investigated in regard to crystal phase. High levels of shear piezoelectric activity, d15 or d24 >2000 pC N−1, has been observed for single domain rhombohedral (R), orthorhombic (O) and tetragonal (T) relaxor-PT crystals. The high piezoelectric response is attributed to a flattening of the Gibbs free energy at compositions proximate to the morphotropic phase boundaries, where the polarization rotation is easy with applying perpendicular electric field. The shear piezoelectric behavior of pervoskite ferroelectric crystals was discussed with respect to ferroelectric-ferroelectric phase transitions and dc bias field using phenomenological approach. The relationship between single domain shear piezoelectric response and piezoelectric activities in domain engineered configurations were given in this paper. From an application viewpoint, the temperature and ac field drive stability for shear piezoelectric responses are investigated. A temperature independent shear piezoelectric response (d24, in the range of −50°C to O-T phase transition temperature) is thermodynamically expected and experimentally confirmed in orthorhombic relaxor-PT crystals; relatively high ac field drive stability (5 kV cm−1) is obtained in manganese modified relaxor-PT crystals. For all thickness shear vibration modes, the mechanical quality factor Qs are less than 50, corresponding to the facilitated polarization rotation.

Electromechanical properties of Al0.9Sc0.1N thin films evaluated at 2.5 GHz film bulk acoustic resonators

Abstract: AlN films are employed in RF filters for wireless communication. We report on enhanced coupling factors kt2 obtained by partial substitution of Al by Sc. Al0.88Sc0.12N films were deposited by reactive magnetron sputtering from an Al0.9Sc0.1 alloy target. They grew in the piezoelectric wurtzite phase with a similar microstructure as pure AlN films. The clamped d33,f increased considerably from 5.1 to 7.8 pm/V. The admittance measured at thin film bulk acoustic wave resonators was fitted to an equivalent circuit model and to 2-dimensional finite element simulation, yielding a kt2 of 7.3% and a quality factor of 650. The material softens considerably.

Surface piezoelectricity: Size effects in nanostructures and the emergence of piezoelectricity in non-piezoelectric materials

Abstract: In this work, using a combination of a theoretical framework and atomistic calculations, we highlight the concept of “surface piezoelectricity,” which can be used to interpret the piezoelectricity of nanostructures. Focusing on three specific material systems (ZnO, SrTiO3, and BaTiO3), we discuss the renormalization of apparent piezoelectric behavior at small scales. In a rather interesting interplay of symmetry and surface effects, we show that nanostructures of certain non-piezoelectric materials may also exhibit piezoelectric behavior. Finally, for the case of ZnO, using a comparison with first principles calculations, we also comment on the fidelity of the widely used core–shell interatomic potentials to capture non-bulk electro-mechanical response.