Showing papers on "Piezoelectricity published in 2014"
TL;DR: It is shown that cyclic stretching and releasing of thin MoS2 flakes with an odd number of atomic layers produces oscillating piezoelectric voltage and current outputs, whereas no output is observed for flakes with even number of layers, which may enable the development of applications in powering nanodevices, adaptive bioprobes and tunable/stretchable electronics/optoelectronics.
Abstract: The two-dimensional semiconducting material molybdenum disulphide shows strong piezoelectricity in its single-layered form, suggesting possible applications in nanoscale electromechanical devices for sensing and energy harvesting. Two-dimensional semiconducting materials are the focus of much research effort thanks to their unusual and potentially useful physical properties. Wenzhou Wu and colleagues now confirm theoretical expectations that one such material — molybdenum disulphide — exhibits strong piezoelectricity in its single-layered form. Such a coupling of mechanical and electrical properties suggests possible applications in nanoscale electromechanical devices for sensing and energy harvesting. The piezoelectric characteristics of nanowires, thin films and bulk crystals have been closely studied for potential applications in sensors, transducers, energy conversion and electronics1,2,3. With their high crystallinity and ability to withstand enormous strain4,5,6, two-dimensional materials are of great interest as high-performance piezoelectric materials. Monolayer MoS2 is predicted to be strongly piezoelectric, an effect that disappears in the bulk owing to the opposite orientations of adjacent atomic layers7,8. Here we report the first experimental study of the piezoelectric properties of two-dimensional MoS2 and show that cyclic stretching and releasing of thin MoS2 flakes with an odd number of atomic layers produces oscillating piezoelectric voltage and current outputs, whereas no output is observed for flakes with an even number of layers. A single monolayer flake strained by 0.53% generates a peak output of 15 mV and 20 pA, corresponding to a power density of 2 mW m−2 and a 5.08% mechanical-to-electrical energy conversion efficiency. In agreement with theoretical predictions, the output increases with decreasing thickness and reverses sign when the strain direction is rotated by 90°. Transport measurements show a strong piezotronic effect in single-layer MoS2, but not in bilayer and bulk MoS2. The coupling between piezoelectricity and semiconducting properties in two-dimensional nanomaterials may enable the development of applications in powering nanodevices, adaptive bioprobes and tunable/stretchable electronics/optoelectronics.
1,683 citations
TL;DR: A detailed overview of the energy harvesting technologies associated with piezoelectric materials along with the closely related sub-classes of pyroelectrics and ferro-electrics can be found in this article.
Abstract: This review provides a detailed overview of the energy harvesting technologies associated with piezoelectric materials along with the closely related sub-classes of pyroelectrics and ferroelectrics. These properties are, in many cases, present in the same material, providing the intriguing prospect of a material that can harvest energy from multiple sources including vibration, thermal fluctuations and light. Piezoelectric materials are initially discussed in the context of harvesting mechanical energy from vibrations using inertial energy harvesting, which relies on the resistance of a mass to acceleration, and kinematic energy harvesting which directly couples the energy harvester to the relative movement of different parts of a source. Issues related to mode of operation, loss mechanisms and using non-linearity to enhance the operating frequency range are described along with the potential materials that could be employed for harvesting vibrations at elevated temperatures. In addition to inorganic piezoelectric materials, compliant piezoelectric materials are also discussed. Piezoelectric energy harvesting devices are complex multi-physics systems requiring advanced methodologies to maximise their performance. The research effort to develop optimisation methods for complex piezoelectric energy harvesters is then reviewed. The use of ferroelectric or multi-ferroic materials to convert light into chemical or electrical energy is then described in applications where the internal electric field can prevent electron–hole recombination or enhance chemical reactions at the ferroelectric surface. Finally, pyroelectric harvesting generates power from temperature fluctuations and this review covers the modes of pyroelectric harvesting such as simple resistive loading and Olsen cycles. Nano-scale pyroelectric systems and novel micro-electro-mechanical-systems designed to increase the operating frequency are discussed.
882 citations
TL;DR: An overview of piezoelectric polymers based on their operating principle is given in this paper, which includes three main categories: bulk polymers, piezocomposites and voided charged polymers.
Abstract: Polymer based MEMS and microfluidic devices have the advantages of mechanical flexibility, lower fabrication cost and faster processing over silicon based ones. Also, many polymer materials are considered biocompatible and can be used in biological applications. A valuable class of polymers for microfabricated devices is piezoelectric functional polymers. In addition to the normal advantages of polymers, piezoelectric polymers can be directly used as an active material in different transduction applications. This paper gives an overview of piezoelectric polymers based on their operating principle. This includes three main categories: bulk piezoelectric polymers, piezocomposites and voided charged polymers. State-of-the-art piezopolymers of each category are presented with a focus on fabrication techniques and material properties. A comparison between the different piezoelectric polymers and common inorganic piezoelectric materials (PZT, ZnO, AlN and PMN?PT) is also provided in terms of piezoelectric properties. The use of piezopolymers in different electromechanical devices is also presented. This includes tactile sensors, energy harvesters, acoustic transducers and inertial sensors.
778 citations
TL;DR: This paper reviews the current state of research on piezoelectric energy harvesting devices for low frequency (0–100 Hz) applications and the methods that have been developed to improve the power outputs of the piezoesterday's energy harvesters.
Abstract: In an effort to eliminate the replacement of the batteries of electronic devices that are difficult or impractical to service once deployed, harvesting energy from mechanical vibrations or impacts using piezoelectric materials has been researched over the last several decades. However, a majority of these applications have very low input frequencies. This presents a challenge for the researchers to optimize the energy output of piezoelectric energy harvesters, due to the relatively high elastic moduli of piezoelectric materials used to date. This paper reviews the current state of research on piezoelectric energy harvesting devices for low frequency (0–100 Hz) applications and the methods that have been developed to improve the power outputs of the piezoelectric energy harvesters. Various key aspects that contribute to the overall performance of a piezoelectric energy harvester are discussed, including geometries of the piezoelectric element, types of piezoelectric material used, techniques employed to match the resonance frequency of the piezoelectric element to input frequency of the host structure, and electronic circuits specifically designed for energy harvesters.
506 citations
TL;DR: A highly stretchable hybrid nanogenerator has been developed using a micro-patterned piezoelectric polymer P(VDF-TrFE), PDMS-CNT composite, and graphene nanosheets that generates very stable piezOElectric and pyroelectric power outputs due to micro- pattern designing.
Abstract: A highly stretchable hybrid nanogenerator has been developed using a micro-patterned piezoelectric polymer P(VDF-TrFE), PDMS-CNT composite, and graphene nanosheets. Mechanical and thermal energies are simultaneously harvested from a single cell of the device. The hybrid nanogenerator exhibits high robustness behavior even after 30% stretching and generates very stable piezoelectric and pyroelectric power outputs due to micro-pattern designing.
462 citations
TL;DR: In this paper, the electrostrictive effect of perovskite solid solutions was systematically surveyed and the techniques for measuring the effect of electrostriction on the piezoelectric activity of these materials were presented.
Abstract: Electrostriction plays an important role in the electromechanical behavior of ferroelectrics and describes a phenomenon in dielectrics where the strain varies proportional to the square of the electric field/polarization. Perovskite ferroelectrics demonstrating high piezoelectric performance, including BaTiO3, Pb(Zr1-xTix)O3, and relaxor-PbTiO3 materials, have been widely used in various electromechanical devices. To improve the piezoelectric activity of these materials, efforts have been focused on the ferroelectric phase transition regions, including shift the composition to the morphotropic phase boundary or shift polymorphic phase transition to room temperature. However, there is not much room left to further enhance the piezoelectric response in perovskite solid solutions using this approach. With the purpose of exploring alternative approaches, the electrostrictive effect is systematically surveyed in this paper. Initially, the techniques for measuring the electrostrictive effect are given and compa...
374 citations
TL;DR: In this article, the state-of-the-art in piezoelectric single crystals for ultrasonic transducer applications is reviewed, and various biomedical applications including eye imaging, intravascular imaging, blood flow measurement, photoacoustic imaging and microbeam applications of the single crystal transducers are discussed.
262 citations
TL;DR: In this article, a beam-based paradigmatical design was proposed for flexoelectric energy harvesting under harmonic mechanical excitation. And the authors showed that the output power density and conversion efficiency increase significantly when the beam thickness reduces from micro-to nanoscale and flexolectricity-based energy harvesting can be a viable alternative to piezoelectrics.
256 citations
237 citations
TL;DR: In this article, a knitted single-structure piezoelectric generator consisting of high β-phase (∼80%) polyamide multifilaments as the spacer yarn interconnected between silver (Ag) coated polyamide multilament yarn layers acting as the top and bottom electrodes is presented.
Abstract: The piezoelectric effect in poly(vinylidene fluoride), PVDF, was discovered over four decades ago and since then, significant work has been carried out aiming at the production of high β-phase fibres and their integration into fabric structures for energy harvesting. However, little work has been done in the area of production of “true piezoelectric fabric structures” based on flexible polymeric materials such as PVDF. In this work, we demonstrate “3D spacer” technology based all-fibre piezoelectric fabrics as power generators and energy harvesters. The knitted single-structure piezoelectric generator consists of high β-phase (∼80%) piezoelectric PVDF monofilaments as the spacer yarn interconnected between silver (Ag) coated polyamide multifilament yarn layers acting as the top and bottom electrodes. The novel and unique textile structure provides an output power density in the range of 1.10–5.10 μW cm−2 at applied impact pressures in the range of 0.02–0.10 MPa, thus providing significantly higher power outputs and efficiencies over the existing 2D woven and nonwoven piezoelectric structures. The high energy efficiency, mechanical durability and comfort of the soft, flexible and all-fibre based power generator are highly attractive for a variety of potential applications such as wearable electronic systems and energy harvesters charged from the ambient environment or by human movement.
230 citations
TL;DR: Clear evidence is found via piezoresponse force microscopy and quantum mechanical calculations that both atomically thin and layered graphitic carbon nitride, or grapheneNitride, nanosheets exhibit anomalous piezoelectricity.
Abstract: Piezoelectricity is a unique property of materials that permits the conversion of mechanical stimuli into electrical and vice versa. On the basis of crystal symmetry considerations, pristine carbon nitride (C3N4) in its various forms is non-piezoelectric. Here we find clear evidence via piezoresponse force microscopy and quantum mechanical calculations that both atomically thin and layered graphitic carbon nitride, or graphene nitride, nanosheets exhibit anomalous piezoelectricity. Insights from ab inito calculations indicate that the emergence of piezoelectricity in this material is due to the fact that a stable phase of graphene nitride nanosheet is riddled with regularly spaced triangular holes. These non-centrosymmetric pores, and the universal presence of flexoelectricity in all dielectrics, lead to the manifestation of the apparent and experimentally verified piezoelectric response. Quantitatively, an e11 piezoelectric coefficient of 0.758 C m(-2) is predicted for C3N4 superlattice, significantly larger than that of the commonly compared α-quartz.
TL;DR: In this article, a new class of active elastic metamaterials with negative capacitance piezoelectric shunting is presented, which can be used for band gap control of both the longitudinal and bending waves.
Abstract: Elastic metamaterials have been extensively investigated due to their significant effects on controlling propagation of elastic waves. One of the most interesting properties is the generation of band gaps, in which subwavelength elastic waves cannot propagate through. In the study, a new class of active elastic metamaterials with negative capacitance piezoelectric shunting is presented. We first investigated dispersion curves and band gap control of an active mass-in-mass lattice system. The unit cell of the mass-in-mass lattice system consists of the inner masses connected by active linear springs to represent negative capacitance piezoelectric shunting. It was demonstrated that the band gaps can be actively controlled and tuned by varying effective stiffness constant of the linear spring through appropriately selecting the value of negative capacitance. The promising application was then demonstrated in the active elastic metamaterial plate integrated with the negative capacitance shunted piezoelectric patches for band gap control of both the longitudinal and bending waves. It can be found that the location and the extent of the induced band gap of the elastic metamaterial can be effectively tuned by using shunted piezoelectric patch with different values of negative capacitance, especially for extremely low-frequency cases.
TL;DR: In this article, it was shown that 90° domain wall motion during both strong (above coercive) and weak (below coercive) electric fields is greatest at these intermediate grain sizes, correlating with the enhanced permittivity and piezoelectric properties observed in BaTiO3.
Abstract: The dielectric and piezoelectric properties of ferroelectric polycrystalline materials have long been known to be strong functions of grain size and extrinsic effects such as domain wall motion. In BaTiO3, for example, it has been observed for several decades that the piezoelectric and dielectric properties are maximized at intermediate grain sizes (≈1 μm) and different theoretical models have been introduced to describe the physical origin of this effect. Here, using in situ, high-energy X-ray diffraction during application of electric fields, it is shown that 90° domain wall motion during both strong (above coercive) and weak (below coercive) electric fields is greatest at these intermediate grain sizes, correlating with the enhanced permittivity and piezoelectric properties observed in BaTiO3. This result validates the long-standing theory in attributing the size effects in polycrystalline BaTiO3 to domain wall displacement. It is now empirically established that a doubling or more in the piezoelectric and dielectric properties of polycrystalline ferroelectric materials can be achieved through domain wall displacement effects; such mechanisms are suggested for use in the design of new ferroelectric materials with enhanced properties.
TL;DR: In this article, the dielectric and electromechanical properties of 0.75Bi1/2Na 1/2TiO3 (25ST) as a function of temperature and frequency were studied.
Abstract: The dielectric and electromechanical properties of 0.75Bi1/2Na1/2TiO3–0.25 SrTiO3 (25ST) as a function of temperature and frequency were studied. It is shown that the 25ST is a relaxor ferroelectric as evidenced by the temperature-dependent dielectric relaxations with an incipient piezoelectricity featured by the presence of a reversible electric-field-induced phase transformation at room temperature. The transition occurs on a broad electric field strength range depending on field amplitude and frequency. It is also accompanied by a huge strain that is attributed to repetitive poling and depoling originating due to the reversibility of the phase transition. The 25ST makes an attractive lead-free candidate for stack actuators as it presents a high normalized d33* of ~600 pm/V at a low electric field of 4 kV/mm for frequencies ranging from 0.1 up to 100 Hz.
TL;DR: In this article, an analytical solution for the simply supported piezoelectric nanoshell by representing displacement components in the double Fourier series was given for a simply supported PNE, and the differential quadrature method was employed to obtain numerical solutions of PNEs under various boundary conditions.
TL;DR: Imidazolium periodate (IPI) is found to be an improper ferroelectric that shows bistable properties simultaneously in three channels of dielectricity, piezoelectricities, and second-harmonic generation within the temperature window 300-310 K.
Abstract: Imidazolium periodate (IPI) is found to be an improper ferroelectric. It shows bistable properties simultaneously in three channels of dielectricity, piezoelectricity, and second-harmonic generation within the temperature window 300-310 K.
TL;DR: New piezoelectric composite transducers have been developed with optimized composite components that have improved thermal stability and mechanical quality factors, making them promising candidates for high temperature, highPower transducer applications, such as therapeutic ultrasound, high power ultrasonic wirebonding, high temperature non-destructive testing, and downhole energy harvesting.
Abstract: Piezoelectric composites are a class of functional materials consisting of piezoelectric active materials and non-piezoelectric passive polymers, mechanically attached together to form different connectivities. These composites have several advantages compared to conventional piezoelectric ceramics and polymers, including improved electromechanical properties, mechanical flexibility and the ability to tailor properties by using several different connectivity patterns. These advantages have led to the improvement of overall transducer performance, such as transducer sensitivity and bandwidth, resulting in rapid implementation of piezoelectric composites in medical imaging ultrasounds and other acoustic transducers. Recently, new piezoelectric composite transducers have been developed with optimized composite components that have improved thermal stability and mechanical quality factors, making them promising candidates for high temperature, high power transducer applications, such as therapeutic ultrasound, high power ultrasonic wirebonding, high temperature non-destructive testing, and downhole energy harvesting. This paper will present recent developments of piezoelectric composite technology for high temperature and high power applications. The concerns and limitations of using piezoelectric composites will also be discussed, and the expected future research directions will be outlined.
TL;DR: In this paper, a Bernoulli-Euler beam model is proposed to investigate the electromechanical coupling response of piezoelectric nanostructures, in which the effects of surface elasticity, dielectricity and pieziolectricness as well as bulk flexoelectoricity are all taken into consideration.
Abstract: The effects of surface and flexoelectricity have been found in the presence of strong size dependence and should be technically taken into account for nano-scaled dielectric structures. This paper proposes a Bernoulli–Euler beam model to investigate the electromechanical coupling response of piezoelectric nanostructures, in which the effects of surface elasticity, dielectricity and piezoelectricity as well as bulk flexoelectricity are all taken into consideration. The governing equations with non-classical boundary conditions are naturally derived from a variational principle. Then the present beam model is directly applied to solve the static bending problems of cantilever beams. Without considering the residual surface stresses, the bending rigidity can be defined the same as that in classical piezoelectricity theory. The bending rigidity is found to increase for silicon nanowires and decrease for silver nanowires. Also the flexoelectric effect in piezoelectric nanowires has a momentous influence on the bending rigidity. The residual surface stresses which are usually neglected are found to be more important than the surface elasticity for the bending of nanowires. However, this has no influence on the effective electromechanical coupling coefficient. The deflections reveal the significance of the residual surface stresses and the bulk flexoelectric effects. The effective electromechanical coupling coefficient for piezoelectric nanowires is dramatically enhanced, which demonstrates the significant effects of the bulk flexoelectricity and surface piezoelectricity. The effects of surface and flexoelectricity decrease with the increase of the beam thickness, and therefore these effects can be ignored for large-scale structures. This work is very helpful in designing cantilever-beam-based nano-electro-devices.
TL;DR: It is found that the major mechanism involved corresponds to screening of the internal electric fields by light-induced charges, which in turn induces stress by inverse piezoelectric effect, which opens new perspectives for the use of ferroelectric oxides in ultrahigh frequency acoustic devices and the development of new GHz-THz acoustic sources.
Abstract: Generation of strain using light is a key issue for future development of ultrasonic devices. Up to now, photo-induced GHz-THz acoustic phonons have been mainly explored in metals and semiconductors, and in artificial nanostructures to enhance their phononic emission. However, despite their inherent strong polarization (providing natural asymmetry) and superior piezoelectric properties, ferroelectric oxides have been only poorly regarded. Here, by using ultrafast optical pump-probe measurements, we show that photogeneration/photodetection of coherent phonons in BiFeO3 ferroelectric leads, at room temperature, to the largest intensity ratio ever reported of GHz transverse acoustic wave versus the longitudinal one. It is found that the major mechanism involved corresponds to screening of the internal electric fields by light-induced charges, which in turn induces stress by inverse piezoelectric effect. This giant opto-acoustic response opens new perspectives for the use of ferroelectric oxides in ultrahigh frequency acoustic devices and the development of new GHz-THz acoustic sources.
TL;DR: In this article, a size-dependent functionally graded piezoelectric beam model was developed using a variational formulation based on the modified strain gradient theory and Timoshenko beam theory.
TL;DR: The manipulation flexibility of this method indicated the potential for customized needs in the application of bone substitute, exhibiting the ability to produce an oriented long-range ordered architecture.
TL;DR: In this paper, the intrinsic piezoelectric response of lead-free Ba(Zr0.2Ti0.8)O3-x(Ba0.7Ca0.3)TiO3 (BZT-xBCT) ceramics has been investigated as a function of composition by using Rayleigh analysis under subswitching-electric field in combination with large-electric-field strain measurement.
Abstract: The piezoelectric activity of lead-free Ba(Zr0.2Ti0.8)O3-x(Ba0.7Ca0.3)TiO3 (BZT-xBCT) ceramics has been investigated as a function of composition by using Rayleigh analysis under subswitching-electric-field in combination with large-electric-field strain measurement. The result shows that the intrinsic piezoelectric response exhibits peak values in the vicinity of composition-induced R (rhombohedral)-MPB (morphotropic phase boundary) and MPB-T (tetragonal) phase transitions, but being much less than total d33 value. On the other hand, the extrinsic piezoelectric response, especially the one associated with reversible domain wall motion, has been greatly enhanced in the phase instability regime. Our results indicate that the extrinsic piezoelectric activity is the major contributor to the high piezoelectricity in BZT-xBCT ceramics.
TL;DR: By comparing dielectric, structural, lattice dynamical, and piezoelectric measurements on PZT and PMN-xPT, two nearly identical compounds that represent weak and strong random electric field limits, it is shown that quenched (static) random fields establish the relaxor phase and identify the order parameter.
Abstract: PbZr1–xTixO3 (PZT) and Pb(Mg1/3Nb2/3)1–xTixO3 (PMN-xPT) are complex lead-oxide perovskites that display exceptional piezoelectric properties for pseudorhombohedral compositions near a tetragonal phase boundary. In PZT these compositions are ferroelectrics, but in PMN-xPT they are relaxors because the dielectric permittivity is frequency dependent and exhibits non-Arrhenius behavior. We show that the nanoscale structure unique to PMN-xPT and other lead-oxide perovskite relaxors is absent in PZT and correlates with a greater than 100% enhancement of the longitudinal piezoelectric coefficient in PMN-xPT relative to that in PZT. By comparing dielectric, structural, lattice dynamical, and piezoelectric measurements on PZT and PMN-xPT, two nearly identical compounds that represent weak and strong random electric field limits, we show that quenched (static) random fields establish the relaxor phase and identify the order parameter.
TL;DR: In this article, the dispersion characteristics of elastic waves propagating in a monolayer piezoelectric nanoplate are investigated with consideration of the surface PAs as well as the nonlocal small-scale effect.
Abstract: In this paper, the dispersion characteristics of elastic waves propagating in a monolayer piezoelectric nanoplate is investigated with consideration of the surface piezoelectricity as well as the nonlocal small-scale effect. Nonlocal electroelasticity theory is used to derive the general governing equations by introducing an intrinsic length, and the surface effects exerting on the boundary conditions of the piezoelectric nanoplate are taken into account through incorporation of the surface piezoelectricity model and the generalized Young–Laplace equations. The dispersion relations of elastic waves based on the current formulation are obtained in an explicit closed form. Numerical results show that both the nonlocal scale parameter and surface piezoelectricity have significant influence on the size-dependent properties of dispersion behaviors. It is also found that there exists an escape frequency above which the waves may not propagate in the piezoelectric plate with nanoscale thickness.
TL;DR: In this paper, an improved piezoelectric properties, energy harvesting performance, lower coercive fields, and the polarization orientation of poly(vinylidene fluoride-trifluoroethylene) (PVDF-TrFE) nanotubes synthesized with nanoconfinement effect are reported.
Abstract: 1D nanostructures of soft ferroelectric materials exert promising potential in the fields of energy harvesting and flexible and printed nanoelectronics. Here, improved piezoelectric properties, energy-harvesting performance, lower coercive fields, and the polarization orientation of poly(vinylidene fluoride–trifluoroethylene) (PVDF-TrFE) nanotubes synthesized with nanoconfinement effect are reported. X-ray diffraction (XRD) patterns of the nanotubes show the peak corresponding to the planes of (110)/(200), which is a signature of ferroelectric beta phase formation. Piezoforce spectroscopy measurements on the free-standing horizontal nanotubes bundles reveal that the effective polarization direction is oriented at an inclination to the long axis of the nanotubes. The nanotubes exhibit a coercive field of 18.6 MV m−1 along the long axis and 40 MV m−1 (13.2 MV m−1 considering the air gap) in a direction perpendicular to the long axis, which is lower than the film counterpart of 50 MV m−1. The poled 200 nm nanotubes, with 40% reduction in poling field, give larger piezoelectric d33 coefficient values of 44 pm V−1, compared to poled films (≈20 pm V−1). The ferroelectric nanotubes deliver superior energy harvesting performance with an output voltage of ≈4.8 V and power of 2.2 μW cm−2, under a dynamic compression pressure of 0.075 MPa at 1 Hz.
TL;DR: In this paper, a thermodynamic analysis for diffusionless phase diagrams of ferroelectric solid solutions that display a morphotropic phase boundary separating adjacent tetragonal and rhombohedral phases is presented.
Abstract: A thermodynamic analysis is presented for the diffusionless phase diagrams of ferroelectric solid solutions that display a morphotropic phase boundary (MPB) separating adjacent tetragonal and rhombohedral phases. Equations are developed for the shape of the MPB, the locations of triple and tricritical points, and for the line along which the anisotropy of polarization vanishes. The appearance of lower symmetry orthorhombic and monoclinic phases is considered and the topologies of energy surfaces in the region of the phase diagram where these phases may stabilize are illustrated. The theory is applied to the solid solution of lead zirconate with lead titanate (PZT) and relationships between polar anisotropy and the transformation strain, dielectric susceptibility and piezoelectric properties, are discussed. The analysis is used to reproduce phase boundary lines for solid solutions of lead titanate with lead magnesium niobate (PMN-PT) and lead zinc niobate (PZN-PT) and composition–temperature diagrams along isopleths in the ternary system PMN-PZT are estimated. The anisotropies of polarization in solid solutions based on lead titanate and barium titanate are contrasted. The results provide a thermodynamic framework useful for guiding experimental investigations of ferroelectric solid solutions and for generating energy functions used in constitutive modeling and phase field simulations of microstructure and properties.
TL;DR: In this article, an impact-induced resonance was proposed to enable effective excitation of the piezoelectric cantilevers' vibration modes and obtain optimum deformation, which enhances the mechanical/electrical energy transformation.
Abstract: To improve the output power of a rotational piezoelectric wind energy harvester, impact-induced resonance is proposed to enable effective excitation of the piezoelectric cantilevers' vibration modes and obtain optimum deformation, which enhances the mechanical/electrical energy transformation. The impact force is introduced by forming a piezoelectric bimorph cantilever polygon that is fixed at the circumference of the rotating fan's internal surface. Elastic balls are placed inside the polygon. When wind rotates the device, the balls strike the piezoelectric cantilevers, and thus electricity is generated by the piezoelectric effect. The impact point is carefully chosen to use the first bending mode as much as possible, and thus maximize the harvesting efficiency. The design enables each bimorph to be struck in a similar area and every bimorph is struck in that area at different moments. As a result, a relatively stable output frequency can be obtained. The output frequency can also be changed by choosing different bimorph dimensions, which will also make the device simpler and the costs lower. A prototype piezoelectric energy harvester consisting of twelve piezoelectric cantilevers was constructed. The piezoelectric cantilevers were made from phosphor bronze, the lead zirconium titanate (PZT)-based bimorph cantilever had dimensions of 47 mm × 20 mm × 0.5 mm, and the elastic balls were made from steel with a diameter of 10 mm. The optimal DC output power was 613 μW across the 20 kΩ resistor at a rotation speed of 200 r/min with an inscribed circle diameter of 31 mm.
TL;DR: PVDF nanoribbons are promising structures for constructing devices such as highly efficient energy generators, large area pressure sensors, artificial muscle and skin, due to the unique geometry and extended lengths, high polar phase content, high thermal stability and high piezoelectric coefficient.
Abstract: We produced kilometer-long, endlessly parallel, spontaneously piezoelectric and thermally stable poly(vinylidene fluoride) (PVDF) micro- and nanoribbons using iterative size reduction technique based on thermal fiber drawing. Because of high stress and temperature used in thermal drawing process, we obtained spontaneously polar γ phase PVDF micro- and nanoribbons without electrical poling process. On the basis of X-ray diffraction (XRD) analysis, we observed that PVDF micro- and nanoribbons are thermally stable and conserve the polar γ phase even after being exposed to heat treatment above the melting point of PVDF. Phase transition mechanism is investigated and explained using ab initio calculations. We measured an average effective piezoelectric constant as -58.5 pm/V from a single PVDF nanoribbon using a piezo evaluation system along with an atomic force microscope. PVDF nanoribbons are promising structures for constructing devices such as highly efficient energy generators, large area pressure sensors, artificial muscle and skin, due to the unique geometry and extended lengths, high polar phase content, high thermal stability and high piezoelectric coefficient. We demonstrated two proof of principle devices for energy harvesting and sensing applications with a 60 V open circuit peak voltage and 10 μA peak short-circuit current output.
TL;DR: In this article, a review of the literature on lead-free piezoelectric ceramics is presented, which shows that fatigue under cyclic electrical loading is prevalent in many lead-fertile piezo-lectric ceramic compositions.
Abstract: A considerable body of knowledge now exists from studies involving the development of lead-free piezoelectric ceramics and a number of high potential alternatives to current lead-based materials have been identified. Stability under cyclic electric fields is an important property of piezoelectric materials. Here, we review the research to date which shows that fatigue under cyclic electrical loading is prevalent in many lead-free piezoelectric ceramic compositions. However, the variety of compositions and mechanisms for piezoelectric behavior in these materials corresponds to significant variances in the nature of fatigue degradation and the likely mechanisms thereof, which do not directly parallel those of well-studied lead-based materials. In particular, the use of field-induced phase changes as an actuation mechanism provides distinctive fatigue behaviors. Particular attention is given to fatigue of ferroelectric and relaxor (ergodic and nonergodic) structures and their dependence upon temperature and electric field and the potential design of materials with high fatigue resistance.
TL;DR: In this article, a new additive manufacturing (AM) process was proposed to directly and continuously print piezoelectric devices from polyvinylidene fluoride (PVDF) polymeric filament rods under a strong electric field.
Abstract: This paper presents a new additive manufacturing (AM) process to directly and continuously print piezoelectric devices from polyvinylidene fluoride (PVDF) polymeric filament rods under a strong electric field. This process, called ?electric poling-assisted additive manufacturing or EPAM, combines AM and electric poling processes and is able to fabricate free-form shape piezoelectric devices continuously. In this process, the PVDF polymer dipoles remain well-aligned and uniform over a large area in a single design, production and fabrication step. During EPAM process, molten PVDF polymer is simultaneously mechanically stresses in-situ by the leading nozzle and electrically poled by applying high electric field under high temperature. The EPAM system was constructed to directly print piezoelectric structures from PVDF polymeric filament while applying high electric field between nozzle tip and printing bed in AM machine. Piezoelectric devices were successfully fabricated using the EPAM process. The crystalline phase transitions that occurred from the process were identified by using the Fourier transform infrared spectroscope. The results indicate that devices printed under a strong electric field become piezoelectric during the EPAM process and that stronger electric fields result in greater piezoelectricity as marked by the electrical response and the formation of sharper peaks at the polar ? crystalline wavenumber of the PVDF polymer. Performing this process in the absence of an electric field does not result in dipole alignment of PVDF polymer. The EPAM process is expected to lead to the widespread use of AM to fabricate a variety of piezoelectric PVDF polymer-based devices for sensing, actuation and energy harvesting applications with simple, low cost, single processing and fabrication step.