Showing papers on "Piezoelectricity published in 2015"
1,175 citations
TL;DR: Experimental evidence of piezoelectricity in a free-standing single layer of molybdenum disulphide (MoS₂) and the angular dependence of electromechanical coupling is determined, which determined the two-dimensional crystal orientation.
Abstract: Free-standing monolayers of MoS2 exhibit piezoelectric behaviour due to inversion symmetry breaking. Piezoelectricity allows precise and robust conversion between electricity and mechanical force, and arises from the broken inversion symmetry in the atomic structure1,2,3. Reducing the dimensionality of bulk materials has been suggested to enhance piezoelectricity4. However, when the thickness of a material approaches a single molecular layer, the large surface energy can cause piezoelectric structures to be thermodynamically unstable5. Transition-metal dichalcogenides can retain their atomic structures down to the single-layer limit without lattice reconstruction, even under ambient conditions6. Recent calculations have predicted the existence of piezoelectricity in these two-dimensional crystals due to their broken inversion symmetry7. Here, we report experimental evidence of piezoelectricity in a free-standing single layer of molybdenum disulphide (MoS2) and a measured piezoelectric coefficient of e11 = 2.9 × 10–10 C m−1. The measurement of the intrinsic piezoelectricity in such free-standing crystals is free from substrate effects such as doping and parasitic charges. We observed a finite and zero piezoelectric response in MoS2 in odd and even number of layers, respectively, in sharp contrast to bulk piezoelectric materials. This oscillation is due to the breaking and recovery of the inversion symmetry of the two-dimensional crystal. Through the angular dependence of electromechanical coupling, we determined the two-dimensional crystal orientation. The piezoelectricity discovered in this single molecular membrane promises new applications in low-power logic switches for computing and ultrasensitive biological sensors scaled down to a single atomic unit cell8,9.
663 citations
TL;DR: From statistical analysis, correlations between the piezoelectric coefficients and the electronic and structural properties of the 2D materials that elucidate the origin of the piezolectricity are identified.
Abstract: Two-dimensional (2D) materials present many unique materials concepts, including material properties that sometimes differ dramatically from those of their bulk counterparts. One of these properties, piezoelectricity, is important for micro- and nanoelectromechanical systems applications. Using symmetry analysis, we determine the independent piezoelectric coefficients for four groups of predicted and synthesized 2D materials. We calculate with density-functional perturbation theory the stiffness and piezoelectric tensors of these materials. We determine the in-plane piezoelectric coefficient d11 for 37 materials within the families of 2D metal dichalcogenides, metal oxides, and III–V semiconductor materials. A majority of the structures, including CrSe2, CrTe2, CaO, CdO, ZnO, and InN, have d11 coefficients greater than 5 pm/V, a typical value for bulk piezoelectric materials. Our symmetry analysis shows that buckled 2D materials exhibit an out-of-plane coefficient d31. We find that d31 for 8 III–V semicon...
407 citations
TL;DR: In this paper, a review summarises the work to date on nanostructured piezoelectric energy harvesters, commonly referred to as nanogenerators, starting with early reports of PZO output from single strained ZnO nanorods, and moving through the use of nanorod arrays, flexible substrates and alternative materials and nanostructure.
386 citations
TL;DR: The piezoelectric effect combined with photoelectric conversion realizes an ultrasonic-wave-driven piezophotototronic process in the hybrid photocatalyst, which is the fundamental of sonophotocatalysis.
Abstract: An electric field built inside a crystal was proposed to enhance photoinduced carrier separation for improving photocatalytic property of semiconductor photocatalysts. However, a static built-in electric field can easily be saturated by the free carriers due to electrostatic screening, and the enhancement of photocatalysis, thus, is halted. To overcome this problem, here, we propose sonophotocatalysis based on a new hybrid photocatalyst, which combines ferroelectric nanocrystals (BaTiO3) and semiconductor nanoparticles (Ag2O) to form an Ag2O–BaTiO3 hybrid photocatalyst. Under periodic ultrasonic excitation, a spontaneous polarization potential of BaTiO3 nanocrystals in responding to ultrasonic wave can act as alternating built-in electric field to separate photoinduced carriers incessantly, which can significantly enhance the photocatalytic activity and cyclic performance of the Ag2O–BaTiO3 hybrid structure. The piezoelectric effect combined with photoelectric conversion realizes an ultrasonic-wave-driven...
383 citations
TL;DR: By adding the super-tetragonal bismuth gallium oxide to the compound, the piezoelectric properties are as good as those of lead zirconate titanate ceramics.
Abstract: A bismuth ferrite and barium titanate solid solution compound can achieve good piezoelectric properties with a high Curie temperature when fabricated with low-temperature sintering followed by a water-quenching process, with no complicated grain alignment processes performed. By adding the super-tetragonal bismuth gallium oxide to the compound, the piezoelectric properties are as good as those of lead zirconate titanate ceramics.
367 citations
TL;DR: A review of the current status of development of piezo materials can be found in this article, where a number of lead free piezo ceramics have been explored, such as BNT, BKT, KNN, and BZT-BCT.
Abstract: The growth of piezo science is phenomenal since the discovery of piezoelectricity in 1880. Among various piezoelectric materials, lead zirconate titanate (PZT) is a very popular and exhaustively studied piezo system which allows synthesis of large number of materials with wide range of properties due to formation of solid solutions over large range of Zr:Ti ratio. Also, this system accommodates wide range of dopants for modification of crystal structure. Due to this versatile nature, PZT has emerged as very popular among users and researchers worldwide. However, considering the toxicity of lead oxide, development of lead free piezo ceramics is encouraged in recent years. Some lead free piezo material systems such as BNT, BKT, KNN, BZT-BCT have been explored. However, development of lead free piezo devices and their performance in comparison with PZT devices are yet to be established. At this juncture, it was felt that an article reviewing the current status of development of piezo materials highlighting t...
340 citations
TL;DR: In this article, the photocatalytic activity of ZnO nanowires for degrading methylene blue has been enhanced by the piezoelectric-driven separation of photo-generated carriers.
316 citations
TL;DR: Results not only pave the way for applications of Bi₅TiO₃-based piezoceramics, but also have great impact on the understanding of the mechanism of depolarization so as to provide a new design to optimize the performance of lead-free piezoelectrics.
Abstract: Piezoelectric materials are used as sensors or actuators in many devices. Here, the authors demonstrate that semiconducting ZnO particles embedded into a Bi0.5Na0.5TiO3-based matrix improve its piezoelectric properties, promising an alternative to presently used lead-based materials.
261 citations
TL;DR: In this paper, the effect of grain size, content and other factors under the purview of dielectric and piezoelectric properties while evaluating the sensitivity of the material for sensor application was evaluated.
Abstract: Smart materials, which exhibit piezoelectricity, find an eclectic range of applications in the industry. The direct piezoelectric effect has been widely used in sensor design, and the inverse piezoelectric effect has been applied in actuator design. Ever since 1954, PZT and BaTiO3 were widely used for sensor and actuator applications despite their toxicity, brittleness, inflexibility, etc. With the discovery of PVDF in 1969, followed by development of copolymers, a flexible, easy to process, nontoxic, high density alternate with high piezoelectric voltage coefficient was available. In the past 20 years, heterostructural materials like polymer ceramic composites, have received lot of attention, since these materials combine the excellent pyroelectric and piezoelectric properties of ceramics with the flexibility, processing facility, and strength of the polymers resulting in relatively high dielectric permittivity and breakdown strength, which are not attainable in a single phase piezoelectric material. The current review article is an attempt to provide a compendium of all the work carried out with reference to PVDF-PZT composites. The review article evaluates the effect of grain size, content and other factors under the purview of dielectric and piezoelectric properties while evaluating the sensitivity of the material for sensor application. POLYM. ENG. SCI., 55:1589–1616, 2015. © 2015 Society of Plastics Engineers
242 citations
TL;DR: The experimental observation indicates that the conductivity of MoS2 devices can be actively modulated by the piezoelectric charge polarization-induced built-in electric field under strain variation, providing evidence for strain-gating monolayer MoS3 piezotronics, a promising avenue for achieving augmented functionalities in next-generation electronic and mechanical–electronic nanodevices.
Abstract: High-performance piezoelectricity in monolayer semiconducting transition metal dichalcogenides is highly desirable for the development of nanosensors, piezotronics and photo-piezotransistors. Here we report the experimental study of the theoretically predicted piezoelectric effect in triangle monolayer MoS2 devices under isotropic mechanical deformation. The experimental observation indicates that the conductivity of MoS2 devices can be actively modulated by the piezoelectric charge polarization-induced built-in electric field under strain variation. These polarization charges alter the Schottky barrier height on both contacts, resulting in a barrier height increase with increasing compressive strain and decrease with increasing tensile strain. The underlying mechanism of strain-induced in-plane charge polarization is proposed and discussed using energy band diagrams. In addition, a new type of MoS2 strain/force sensor built using a monolayer MoS2 triangle is also demonstrated. Our results provide evidence for strain-gating monolayer MoS2 piezotronics, a promising avenue for achieving augmented functionalities in next-generation electronic and mechanical-electronic nanodevices.
TL;DR: It is shown that a thorough understanding on the kinetic processes is critical in analyzing energy loss behavior and other time-dependent properties in ferroelectric materials, and a general theoretical model is proposed to describe the inherent relationships among elastic, dielectric, piezoelectric and mechanical losses.
Abstract: Ferroelectric materials are the best dielectric and piezoelectric materials known today. Since the discovery of barium titanate in the 1940s, lead zirconate titanate ceramics in the 1950s and relaxor-PT single crystals (such as lead magnesium niobate-lead titanate and lead zinc niobate-lead titanate) in the 1980s and 1990s, perovskite ferroelectric materials have been the dominating piezoelectric materials for electromechanical devices, and are widely used in sensors, actuators and ultrasonic transducers. Energy losses (or energy dissipation) in ferroelectrics are one of the most critical issues for high power devices, such as therapeutic ultrasonic transducers, large displacement actuators, SONAR projectors, and high frequency medical imaging transducers. The losses of ferroelectric materials have three distinct types, i.e., elastic, piezoelectric and dielectric losses. People have been investigating the mechanisms of these losses and are trying hard to control and minimize them so as to reduce performance degradation in electromechanical devices. There are impressive progresses made in the past several decades on this topic, but some confusions still exist. Therefore, a systematic review to define related concepts and clear up confusions is urgently in need. With this objective in mind, we provide here a comprehensive review on the energy losses in ferroelectrics, including related mechanisms, characterization techniques and collections of published data on many ferroelectric materials to provide a useful resource for interested scientists and engineers to design electromechanical devices and to gain a global perspective on the complex physical phenomena involved. More importantly, based on the analysis of available information, we proposed a general theoretical model to describe the inherent relationships among elastic, dielectric, piezoelectric and mechanical losses. For multi-domain ferroelectric single crystals and ceramics, intrinsic and extrinsic energy loss mechanisms are discussed in terms of compositions, crystal structures, temperature, domain configurations, domain sizes and grain boundaries. The intrinsic and extrinsic contributions to the total energy dissipation are quantified. In domain engineered ferroelectric single crystals and ceramics, polarization rotations, domain wall motions and mechanical wave scatterings at grain boundaries are believed to control the mechanical quality factors of piezoelectric resonators. We show that a thorough understanding on the kinetic processes is critical in analyzing energy loss behavior and other time-dependent properties in ferroelectric materials. At the end of the review, existing challenges in the study and control of losses in ferroelectric materials are analyzed, and future perspective in resolving these issues is discussed.
TL;DR: It is found that the large amount of internal strain present in ScAlN and its intricate relation with electric polarization make configurational sampling and the use of large supercells at different compositions necessary in order to accurately derive the piezoelectric response of the material.
Abstract: We present a computational study of spontaneous polarization and piezoelectricity in Sc(x)Al(1-x)N alloys in the compositional range from x = 0 to x = 0.5, obtained in the context of density functional theory and the Berry-phase theory of electric polarization using large periodic supercells. We report composition-dependent values of piezoelectric coefficients e(ij), piezoelectric moduli d(ij) and elastic constants C(ij). The theoretical findings are complemented with experimental measurement of e33 for a series of sputtered ScAlN films carried out with a piezoelectric resonator. The rapid increase with Sc content of the piezoelectric response reported in previous studies is confirmed for the available data. A detailed description of the full methodology required to calculate the piezoelectric properties of ScAlN, with application to other complex alloys, is presented. In particular, we find that the large amount of internal strain present in ScAlN and its intricate relation with electric polarization make configurational sampling and the use of large supercells at different compositions necessary in order to accurately derive the piezoelectric response of the material.
TL;DR: In this article, it was found that several layer-phase group-III monochalcogenides, including GaS, GaSe, and InSe, are piezoelectric in their monolayer form.
Abstract: It is found that several layer-phase group-III monochalcogenides, including GaS, GaSe, and InSe, are piezoelectric in their monolayer form. First-principles calculations reveal that the piezoelectric coefficients of monolayer GaS, GaSe, and InSe (2.06, 2.30, and 1.46 pm·V™1) are of the same order of magnitude as previously discovered two-dimensional (2D) piezoelectric materials such as boron nitride (BN) and MoS2 monolayers. This study therefore indicates that a strong piezoelectric response can be obtained in a wide range of two-dimensional materials with broken inversion symmetry. The co-existence of piezoelectricity and superior photo-sensitivity in these monochalcogenide monolayer semiconductors means they have the potential to allow for the integration of electromechanical and optical sensors on the same material platform.
TL;DR: A strong increase of piezoelectric response under illumination is observed, consistent with the previously reported giant photoinduced dielectric constant at low frequencies, and it is speculated that an intrinsic charge transfer photoinduced dipole in the perovskite cage may lie at the origin of this effect.
Abstract: We investigate the ferroelectric properties of photovoltaic methylammonium lead halide CH3NH3PbI3 perovskite using piezoelectric force microscopy (PFM) and macroscopic polarization methods. The electric polarization is clearly observed by amplitude and phase hysteresis loops. However, the polarization loop decreases as the frequency is lowered, persisting for a short time only, in the one second regime, indicating that CH3NH3PbI3 does not exhibit permanent polarization at room temperature. This result is confirmed by macroscopic polarization measurement based on a standard capacitive method. We have observed a strong increase of piezoelectric response under illumination, consistent with the previously reported giant photoinduced dielectric constant at low frequencies. We speculate that an intrinsic charge transfer photoinduced dipole in the perovskite cage may lie at the origin of this effect.
TL;DR: In this paper, a flexible piezoelectric energy harvester was used to enable self-powered DBS in mice, which achieved an extremely high current reaching 0.57 mA, which satisfies the high threshold current for real-time DBS of the motor cortex.
Abstract: Deep brain stimulation (DBS) is widely used for neural prosthetics and brain–computer interfacing. Thus far in vivo implantation of a battery has been a prerequisite to supply the necessary power. Although flexible energy harvesters have recently emerged as alternatives to batteries, they generate insufficient energy for operating brain stimulation. Herein, we report a high performance flexible piezoelectric energy harvester by enabling self-powered DBS in mice. This device adopts an indium modified crystalline Pb(In1/2Nb1/2)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3 (PIMNT) thin film on a plastic substrate to transform tiny mechanical motions to electricity. With slight bending, it generates an extremely high current reaching 0.57 mA, which satisfies the high threshold current for real-time DBS of the motor cortex and thereby could efficiently induce forearm movements in mice. The PIMNT based flexible energy harvester could open a new avenue for future in vivo healthcare technology using self-powered biomedical devices.
TL;DR: In this article, a flexible, lead-free, solution-processable and efficient PENG is demonstrated, based on a highly piezoelectric nanocomposite thin film of barium titanate nanoparticles (BT NPs) embedded into a highly crystalline polyvinylidene fluoride-trifluoroethylene (P(VDF-TrFE)) polymer for charge storage.
TL;DR: In this paper, first-principles calculations were performed to investigate the lattice properties of group-IV monochalcogenides, including static dielectric permittivity, elastic and piezoelectric tensors.
Abstract: We use first-principles calculations to investigate the lattice properties of group-IV monochalcogenides. These include static dielectric permittivity, elastic and piezoelectric tensors. For the monolayer, it is found that the static permittivity, besides acquiring a dependence on the interlayer distance, is comparatively higher than in the 3D system. In contrast, it is found that elastic properties are little changed by the lower dimensionality. Poisson ratios relating in-plane deformations are close to zero, and the existence of a negative Poisson ratio is also predicted for the GeS compound. Finally, the monolayer shows piezoelectricity, with piezoelectric constants higher than those recently predicted to occur in other 2D systems, such as hexagonal BN and transition-metal dichalcogenide monolayers.
TL;DR: In this article, a size-dependent functionally graded piezoelectric microplate model is developed based on the modified couple-stress and sinusoidal plate theories, and the effects of power-law index of material gradient, material length-scale parameter, plate aspect ratio, and mechanical and electric loadings on the displacement (deflection), electric potential, stress, electric displacement and natural frequency are demonstrated.
TL;DR: In this paper, it was shown that several layer-phase group-III monochalcogenides, including GaS, GaSe and InSe, are piezoelectric in the monolayer form.
Abstract: We find that several layer-phase group-III monochalcogenides, including GaS, GaSe and InSe, are piezoelectric in the monolayer form. First-principles calculations reveal that the piezoelectric coefficients of monolayer GaS, GaSe and InSe are on the same order of magnitude as the earlier discovered two-dimensional piezoelectric materials, such as BN and MoS2 monolayers. Our study expands the family of two dimensional piezoelectric materials, suggesting that strong piezoelectric response can occur in a wide range of two dimensional materials with broken inversion symmetry. The co-existence of piezoelectricity and superior photo-sensitivity in these two-dimensional semiconductors enables the integration of electromechanical and optical sensors on the same material platform.
TL;DR: In this article, mathematical derivations for unimorph piezoelectric energy harvester are presented Simulation is done using MATLAB and COMSOL Multiphysics software to study the effect of varying the length and shape of the beam to the generated voltage.
TL;DR: A detailed theoretical investigation of the piezoelectric stress and strain coefficients of single layer transition metal dichalcogenides and transition metal dioxides with chemical formula MX2 is presented by using first-principles calculations based on density functional theory as discussed by the authors.
Abstract: Piezoelectricity is a unique material property that allows one to convert mechanical energy into electrical one or vice versa. Transition metal dichalcogenides (TMDC) and transition metal dioxides (TMDO) are expected to have great potential for piezoelectric device applications due to their noncentrosymmetric and two-dimensional crystal structure. A detailed theoretical investigation of the piezoelectric stress (e11) and piezoelectric strain (d11) coefficients of single layer TMDCs and TMDOs with chemical formula MX2 (where M= Cr, Mo, W, Ti, Zr, Hf, Sn and X = O, S, Se, Te) is presented by using first-principles calculations based on density functional theory. We predict that not only the Mo- and W-based members of this family but also the other materials with M= Cr, Ti, Zr and Sn exhibit highly promising piezoelectric properties. CrTe2 has the largest e11 and d11 coefficients among the group VI elements (i.e., Cr, Mo, and W). In addition, the relaxed-ion e11 and d11 coefficients of SnS2 are almost the sa...
TL;DR: In this article, a template-wetting technique was used to exploit the properties of poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE) nanowires for harvesting mechanical energy in nanogenerators.
Abstract: Nanogenerators based on piezoelectric materials convert ever-present mechanical vibrations into electrical power for energetically autonomous wireless and electronic devices. Nanowires of piezoelectric polymers are particularly attractive for harvesting mechanical energy in this way, as they are flexible, lightweight and sensitive to small vibrations. Previous studies have focused exclusively on nanowires grown by electrospinning, but this involves complex equipment, and high voltages of $\approx$ 10 kV that electrically pole the nanowires and thus render them piezoelectric. Here we demonstrate that nanowires of poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) grown using a simple and cost-effective template-wetting technique, can be successfully exploited in nanogenerators without poling. A typical nanogenerator comprising $\approx$ 10$^{10}$ highly crystalline, self-poled, aligned nanowires spanning $\approx$ 2 cm$^2$ is shown to produce a peak output voltage of 3 V at 5.5 nA in response to low-level vibrations. The mechanical-to-electrical conversion efficiency of 11% exhibited by our template-grown nanowires is comparable with the best previously reported values. Our work therefore offers a scalable means of achieving high-performance nanogenerators for the next generation of self-powered electronics.
TL;DR: In this paper, the effect of electric poling on the piezoelectric properties of sintered [xBZT-(1-x)BCT] ceramics is studied with varying poling temperatures and poling fields.
Abstract: Lead free piezoelectric ceramics barium zirconate titanate-barium calcium titanate, [xBZT-(1-x)BCT] (0.48≤ x ≤0.52), were synthesized by sol-gel method. Calcination of the as-synthesized precursor powders resulted in crystalline powders with single-phase perovskite structure at 700°C, which is significantly lower than that obtained by solid-state reaction. Solid-state sintering at 1450°C resulted in highly dense microstructure with ≥95% of the theoretical density. The effect of electric poling on the piezoelectric properties of the sintered [xBZT-(1-x)BCT] ceramics is studied with varying poling temperatures and poling fields. The results indicated that optimized poling conditions are required in enhancing the piezoelectric properties of [xBZT-(1-x)BCT] ceramics. The morphotropic phase boundary (MPB) composition, 0.5BZT-0.5BCT, showed a high remanent polarization (P r) of 12.2μC/cm2 and a low coercive field (E c) of ~0.14kV/mm. The optimized poling conditions resulted in high piezoelectric charge coefficient d 33 ~637pC/N, large electromechanical coupling coefficient k p ~59.6%, a large strain of 0.157%, a large piezoelectric voltage constant g 33 ~29mVm/N for (0.5BZT-0.5BCT) composition. In this report, the excellent piezoelectric properties of the sol-gel derived BZT-BCT ceramics has been analysed and correlated to its structure and poling conditions.
TL;DR: In this paper, the authors investigated the nonlinear dynamic behavior of a bimorph piezoelectric cantilever under low to moderately high mechanical and electrical excitation levels in energy harvesting, sensing, and actuation.
Abstract: Inherent nonlinearities of piezoelectric materials are pronounced in various engineering applications such as sensing, actuation, combined applications for vibration control, and energy harvesting from dynamical systems The existing literature focusing on the dynamics of electroelastic structures made of piezoelectric materials has explored such nonlinearities separately for the problems of mechanical and electrical excitation Similar manifestations of softening nonlinearities have been attributed to purely elastic nonlinear terms, coupling nonlinearities, hysteresis alone, or a combination of these effects by various authors In order to develop a unified nonlinear nonconservative framework with two-way coupling, the present work investigates the nonlinear dynamic behavior of a bimorph piezoelectric cantilever under low to moderately high mechanical and electrical excitation levels in energy harvesting, sensing, and actuation The highest voltage levels, for near resonance investigation, are well below the coercive field A distributed parameter electroelastic model is developed by accounting for softening and dissipative nonlinearities to analyze the primary resonance of a soft (eg, PZT-5A, PZT-5H) piezoelectric cantilever for the fundamental bending mode using the method of harmonic balance Excellent agreement between the model and experimental investigation is found, providing evidence that quadratic stiffness, damping, and electromechanical coupling effects accurately model predominantly observed nonlinear effects in geometrically linear vibration of piezoelectric cantilever beams The backbone curves of both energy harvesting and actuation frequency responses for a PZT-5A cantilever are experimentally found to be dominantly of first order and specifically governed by ferroelastic quadratic softening for a broad range of mechanical and electrical excitation levels Cubic and higher-order nonlinearities become effective only near the physical limits of the brittle and stiff (geometrically linear) bimorph cantilever when excited near resonance
TL;DR: A patterned electrohydrodynamic (EHD) pulling technology was proposed to fabricate a new self-connected, piezoelectric fiber array vertically integrated P(VDF-TrFE) nanogenerator, with a molecular poling orientation fully aligned to the principal excitation for maximized conversion and a well-bridged electrode pair for efficient charge collection.
Abstract: Piezoelectricity based energy harvesting from mechanical vibrations has attracted extensive attention for its potential application in powering wireless mobile electronics recently. Here, a patterned electrohydrodynamic (EHD) pulling technology was proposed to fabricate a new self-connected, piezoelectric fiber array vertically integrated P(VDF-TrFE) nanogenerator, with a molecular poling orientation fully aligned to the principal excitation for maximized conversion and a well-bridged electrode pair for efficient charge collection. The nanogenerator is fabricated in a novel way by applying a voltage across an electrode pair sandwiching an air gap and an array of shallow micropillars, during which the EHD force tends to pull the micropillars upward, generating a microfiber array finally in robust contact with the upper electrode. Such a thermoplastic and EHD deformation of the microfibers, featured simultaneously by an electric field and by a microfiber elongation dominantly vertical to the electrode, leads to a poling orientation of P(VDF-TrFE) well coincident with the principal strain for the generator excited by a force normal to the electrodes. The as-prepared piezoelectric device exhibits an enhanced output voltage up to 4.0 V and a current of 2.6 μA, therefore the piezoelectric voltage was enhanced to 5.4 times that from the bulk film. Under periodic mechanical impact, electric signals are repeatedly generated from the device and used to power a seven-segment indicator, RBGY colored light-emitting diodes, and a large-scale liquid crystal display screen. These results not only provide a tool for fabricating 3D piezoelectric polymers but offer a new type of self-connected nanogenerator for the next generation of self-powered electronics.
TL;DR: In this article, the fundamental theories of piezotronics and piezo-phototronics, forming their basis for electromechancial devices, sensors and energy sciences, were derived starting from the basic equations for piezoelectricity, semiconductor and photoexcitation, and analytical equations for describing the strain-tuned device current.
TL;DR: The observed piezoresponse and achieved strain in graphene are associated with the chemical interaction of graphene's carbon atoms with the oxygen from underlying SiO2.
Abstract: Pristine graphene is not piezoelectric, but adsorbing dopant atoms can induce a piezoresponse by breaking the material’s inversion symmetry. Here the authors demonstrate strong out-of-plane piezoelectricity in graphene on a silica substrate, providing a system for two-dimensional sensing and actuation.
TL;DR: In this paper, the critical roles of Mn-ions in tailoring the electrical and magnetic properties of BiFeO3-based materials are revealed: the introduction of MnO2 into BiFe0.96Sc0.04O3−BaTiO3 induces a dramatic improvement in insulation, piezoelectricity and multiferroicity.
Abstract: A lead-free multiferroic ceramic of BiFe0.96Sc0.04O3–BaTiO3 is a type of ABO3 perovskite structure, belonging to the R3c space group, but exhibiting poor insulation and weak multiferroicity. In this work, the critical roles of Mn-ions in tailoring the electrical and magnetic properties of BiFeO3-based materials are revealed: the introduction of MnO2 into BiFe0.96Sc0.04O3–BaTiO3 induces a dramatic improvement in insulation, piezoelectricity and multiferroicity. New compositions of BiFe0.96Sc0.04O3–BaTiO3 + x mol% MnO2 were synthesized by a conventional solid-state reaction method. All the ceramics possess a perovskite structure, and a morphotropic phase boundary (MPB) of rhombohedral and monoclinic phases is formed at x = 0.5–1.0. The formation of and is noticeably suppressed and the resistivity of the ceramics is increased by ∼100 times after the addition of 0.5–1.0 mol% MnO2, which make the ceramic polarizable and thus give strong ferroelectricity and considerable piezoelectricity. The ceramics with the MPB composition exhibit high electrical insulation (R = 1.2–1.7 × 1010 Ω cm), good piezoelectricity (d33 = 123–143 pC N−1, kp = 0.34–0.35), strong ferroelectricity (Pr = 13.1–17.6 μC cm−2), high Curie temperature (590–596 °C) and excellent temperature stability of piezoelectric and ferroelectric properties. These improvements are greatly associated with the contribution of Mn ions in the ceramics. Surprisingly, sharply enhanced ferromagnetism with Mr = 0.4946 emu g−1 and Ms = 1.0298 emu g−1 is obtained in the ceramic with x = 7.0, almost one thousand times larger than that of an un-doped ceramic. The origin of unusual ferromagnetism is associated with significant changes in magnetic ordering caused by Mn doping. The high magnetoelectric effect (α33 = 429.6 mV cm−1 Oe−1) is obtained after the addition of 2.0 mol% Mn ions. Our study suggests that the present ceramics may have potential applications in advanced memory devices as promising lead-free high temperature piezoelectric and multiferroic materials.
TL;DR: The enhanced piezo-response is attributed to the combined effect of the change in the inherent dipole moment of the electroactive phase containing PVDF itself and H-bonding arising between the Mg-salt filler and PVDF via electrostatic interactions.
Abstract: Polyvinylidene fluoride (PVDF) films are filled with various mass fractions (wt%) of hydrated metal salt (MgCl2·6H2O) (Mg-salt) to fabricate high performance piezoelectric energy harvesters (PEHs). They deliver up to 4 V of open circuit voltage by simply repeated human finger imparting (under a pressure of ∼4.45 kPa) and also generate sufficient power to turn on at least ten commercial blue light emitting diodes (LEDs) instantly. The enhanced piezo-response is attributed to the combined effect of the change in the inherent dipole moment of the electroactive phase containing PVDF itself and H-bonding arising between the Mg-salt filler and PVDF via electrostatic interactions. Furthermore, it also successfully charged the capacitors, signifying practical applicability as a piezoelectric based energy harvester power source. UV-visible optical absorption spectral analysis revealed the possibility to estimate a change in the optical band gap value at different concentrations of Mg-salt filler added PVDF films that possess a useful methodology where the Mg-salt can be used as an optical probe. In addition dielectric properties have been studied to understand the role of molecular kinetic and interfacial polarization occurs in H-bond PVDF films at different applied frequencies at room temperature.