Piezoelectric Phase Research Articles

Design of tunable acoustic metamaterials with periodic piezoelectric microstructure

An innovative special class of tunable periodic metamaterials is designed, suitable for realizing high-performance acoustic filters. The metamaterial is made up of a phononic crystal coupled to local resonators. Such local resonators consist of masses enclosed into piezoelectric rings, shunted by either dissipative or non-dissipative electrical circuit. By tuning the impedance/admittance of such electrical circuits, it is possible to fully adjust the constitutive properties of the shunting piezoelectric material. This feature paves the way for unconventional behaviours, well beyond the capabilities achievable with classical materials. It follows that the acoustic properties of the periodic metamaterial can be adaptively modified, in turn, opening new possibilities for the control of pass and stop bands. By exploiting a generalization of the Floquet–Bloch theory, the in-plane free wave propagation in the tunable metamaterial is investigated, by varying a certain tuning parameter, to show the efficiency of the proposed shunting piezoelectric system as a wave propagation control device. Particular attention is devoted to the determination of the in-plane constitutive equations of the shunting piezoelectric phase in the transformed Laplace space. Finally, broad design directions of tunable acoustic filters aiming to a changing performance requirement in real-time, is also provided.

Magnetoelectrics: Three Centuries of Research Heading towards the 4.0 Industrial Revolution.

Magnetoelectric (ME) materials composed of magnetostrictive and piezoelectric phases have been the subject of decades of research due to their versatility and unique capability to couple the magnetic and electric properties of the matter. While these materials are often studied from a fundamental point of view, the 4.0 revolution (automation of traditional manufacturing and industrial practices, using modern smart technology) and the Internet of Things (IoT) context allows the perfect conditions for this type of materials being effectively/finally implemented in a variety of advanced applications. This review starts in the era of Rontgen and Curie and ends up in the present day, highlighting challenges/directions for the time to come. The main materials, configurations, ME coefficients, and processing techniques are reported.

Piezoelectric β-polymorph formation of new textiles by surface modification with coating process based on interfacial interaction on the conformational variation of poly (vinylidene fluoride) (PVDF) chains

Novel textiles have received a lot of attention from researchers in the last decade due to some of their unique features. The introduction of intelligent materials into textile structures offers an opportunity to develop multifunctional textiles, such as sensing, reacting, conducting electricity and performing energy conversion operations. In this research work nanocomposite-based highly piezoelectric and electroactive β-phase new textile has been developed using the pad-dry-cure method. The deposition of poly (vinylidene fluoride) (PVDF) − carbon nanofillers (CNF) − tetraethyl orthosilicate (TEOS), Si(OCH2CH3)4 was acquired on a treated textile substrate using coating technique followed by evaporation to transform the passive (non-functional) textile into a dynamic textile with an enhanced piezoelectric β-phase. The aim of the study is the investigation of the impact the coating of textile via piezoelectric nanocomposites based PVDF-CNF (by optimizing piezoelectric crystalline phase). The chemical composition of CT/PVDF-CNC-TEOS textile was detected by qualitative elemental analysis (SEM/EDX). The added of 0.5% of CNF during the process provides material textiles with a piezoelectric β-phase of up to 50% has been measured by FTIR experiments. These results indicated that CNF has high efficiency in transforming the phase α introduced in the unloaded PVDF, to the β-phase in the case of nanocomposites. Consequently, this fabricated new textile exhibits glorious piezoelectric β-phase even with relatively low coating content of PVDF-CNF-TEOS. The study demonstrates that the pad-dry-cure method can potentially be used for the development of piezoelectric nanocomposite-coated wearable new textiles for sensors and energy harvesting applications. We believe that our study may inspire the research area for future advanced applications.

Apparent Flexoelectricity Due to Heterogeneous Piezoelectricity

Abstract Recent work has highlighted how the phenomenon of flexoelectricity can masquerade as piezoelectricity. This notion can not only be exploited to create artificial piezoelectric-like materials without using piezoelectric materials but may also explain measurement artifacts in dielectrics. In this article, we show that the reverse is also possible and potentially advantageous in certain situations (such as energy harvesting). By constructing a computational homogenization approach predicated on the finite element method, we argue that composites made of piezoelectric phases can conspire to endow the material with a distinct overall flexoelectric-like response even though the native flexoelectricity of the constituent materials is negligible. Full finite element procedures for numerical evaluation of the different effective tensors, including the flexoelectric tensor, are provided. Numerical investigations are conducted, showing variation of the effective flexoelectric properties with respect to local geometry and properties of the composite in piezoelectric–piezoelectric and polymer–piezoelectric composites. We find that the flexoelectric response can be tuned to nearly five times higher than the constituents.

Experimentally validated model and power optimization of a magnetoelectric wireless power transfer system in free-free configuration

This article presents a thorough analysis and an equivalent circuit model of a wireless power transfer system utilizing magnetoelectric (ME) effects. Based on two-port theory, explicit analytical solutions of, (i) the ME coefficient (defined by the derivative of the generated electric field with respect to the applied magnetic field), and (ii) the power transferred to a load resistance, are derived and rigorously validated by experiments. The compact closed-forms of the optimal load and its corresponding maximum output power are developed. In our particular experimental system, a power of ∼10 mW is attained at an applied magnetic flux density of 318.9 µT with a laminated composite made by two Galfenol and one PZT layers. While is widely used in the literature as a standard criterion to evaluate the performance of a ME transducer, we reveal that larger does not always ensure higher optimum power delivered to the load. Instead, we quantify the essential influences of each magnetostrictive and piezoelectric phases on the maximum obtainable power. We show that the transduction factor between the magnetic and mechanical domains is often more critical for power optimization than the mechanical-electrical transduction factor as it determines and limits the maximum power available for transfer to a resistive load.

Piezotronic effect boosted photocatalytic performance of heterostructured BaTiO3/TiO2 nanofibers for degradation of organic pollutants

The effective separation of photo-generated electrons and holes is an important factor that determines the photocatalytic efficiency of the catalysts. Here, we propose a core/shell BaTiO3/TiO2 nanocomposites that present enhanced photocatalytic performance through a piezotronic effect. The polarization generated by the piezoelectric phase in the BaTiO3/TiO2 nanofibers prepared by the electrospinning method under ultrasonic activation dramatically improves the photocatalytic performance of the catalysts. Under the co-excitation of ultrasonic and ultraviolet irradiation, the oxidation rate constant of the polarized BaTiO3/TiO2 nanofibers on RhB dye can reach 9.67 × 10−2 min−1, which is 3.51 times and 3.22 times of the corresponding values of TiO2 nanofibers and BaTiO3/TiO2 nanofibers under only UV irradiation, respectively. This paper provides a promising strategy for improving photocatalytic performance through mechanical vibration and helps to understand the coupling mechanism between piezoelectric and photocatalytic effects.

Piezoelectric domain walls in van der Waals antiferroelectric CuInP2Se6

Polar van der Waals chalcogenophosphates exhibit unique properties, such as negative electrostriction and multi-well ferrielectricity, and enable combining dielectric and 2D electronic materials. Using low temperature piezoresponse force microscopy, we revealed coexistence of piezoelectric and non-piezoelectric phases in CuInP2Se6, forming unusual domain walls with enhanced piezoelectric response. From systematic imaging experiments we have inferred the formation of a partially polarized antiferroelectric state, with inclusions of structurally distinct ferrielectric domains enclosed by the corresponding phase boundaries. The assignment is strongly supported by optical spectroscopies and density-functional-theory calculations. Enhanced piezoresponse at the ferrielectric/antiferroelectric phase boundary and the ability to manipulate this entity with electric field on the nanoscale expand the existing phenomenology of functional domain walls. At the same time, phase-coexistence in chalcogenophosphates may lead to rational strategies for incorporation of ferroic functionality into van der Waals heterostructures, with stronger resilience toward detrimental size-effects.

Flexible textured MnO2 nanorods/ PVDF hybrid films with superior piezoelectric performance for energy harvesting application

To date, the fabrication of high-performance flexible energy harvesters/nanogenerators based on piezoelectric poly(vinyldene fluoride) (PVDF) is of great concern due to their huge potential to realize full-flexible self-powered electronics. Herein, in this work, we report a flexible piezoelectric nanogenerator (PNG) based on a textured hybrid film consisting of PVDF and manganese dioxide (MnO2) nanorods. It is found that the combination of MnO2 and PVDF can notably facilitate the formation of piezoelectric phase, increase the crystallinity and promote the polarization level, inducing dramatically strengthened piezoelectric and output activity for PVDF. Additionally, the addition of MnO2 has the effect of significantly enhancing the mechanical property while slightly increasing dielectric constant of nanocomposites, which are advantageous to further harnessing the output enhancement. With an optimal loading of 1.0 wt% MnO2, the piezoelectric coefficient (d33 ≈ 38 pC/N) and correspondingly output response of hybrid films reached the peak. For instance, under the d33 working mode, an output voltage of 3.2 V can be achieved in hybrid films while that of PVDF is only 1.7 V.

Enhancement of piezoelectric properties of lithium niobate thin films by different annealing parameters

Piezoelectric materials with useful properties find a wide range of applications including opto- and acousto- electronics. Lithium niobate in the form of a thin film is one of those promising materials and has a potential to improve ferroelectric random access memories devices, optical waveguides or acoustic delay lines by virtue of its physical characteristics, e.g. electro-optic coefficient, acoustic velocity, refractive indices etc. The key challenge to overcome is lithium nonstoichiometry as it leads to the appearance of parasite phases and thus aggravates physical and structural properties of a film. According to literature data, in order to obtain microcrystalline piezoelectric phase in previously amorphous films a set of methods is used. In our case we tried to synthesize LN films using congruent target and non-heated silicon substrate and then attain the piezoelectric phase by different annealing parameters. Afterwards LN films were compared to the ones synthesized on the silicon substrate with an additional buffer layer of platinum. Samples were studied by scanning probe microscope. Self-polarization vectors were defined. Based on domain structure images, the histograms of distribution of piezoresponse signals were built.

Nonlocal nonlinear dynamic behavior of composite piezo-magnetic beams using a refined higher-order beam theory

The present paper explores nonlinear dynamical properties of piezo-magnetic beams based on a nonlocal refined higher-order beam formulation and piezoelectric phase effect. The piezoelectric phase increment may lead to improved vibrational behaviors for the smart beams subjected to magnetic fields and external harmonic excitation. Nonlinear governing equations of a nonlocal intelligent beam have been achieved based upon the refined beam model and a numerical provided has been introduced to calculate nonlinear vibrational curves. The present study indicates that variation in the volume fraction of piezoelectric ingredient has a substantial impact on vibrational behaviors of intelligent nanobeam under electrical and magnetic fields. Also, it can be seen that nonlinear free/forced vibrational behaviors of intelligent nanobeam have dependency on the magnitudes of induced electrical voltages, magnetic potential, stiffening elastic substrate and shear deformation.

Polymer Biowaste Hybrid for Enhanced Piezoelectric Energy Harvesting

A green composite, derived from the biowaste pomegranate peel, is used for piezoelectric energy harvesting. A hybrid of poly(vinylidene fluoride) and pomegranate peel powder is prepared through a solution route. A structural change of the polymer matrix from the nonpiezo to piezoelectric phase in the presence of a filler has been revealed through X-ray diffraction, spectroscopic, and calorimetric studies. Piezoelectric biowaste induces piezoelectricity in the polymer matrix, which is further confirmed through a range of morphological studies (optical, electronic, and atomic force microscopy). A model has been developed to focus on the synergism between two piezoelectric phases (matrix and filler), which is appropriate for energy harvesting. A device has been fabricated using the hybrid, which exhibits a high open circuit voltage and a power density of 65 V and 84 μW/cm2. The developed device is also able to generate power under human movements such as walking, twisting, and bending, and the power is sufficient to light up LEDs and can be stored using a capacitor.

Nonlinear vibration characteristics of refined higher-order multi-phase piezo-magnetic nanobeams

This paper studies nonlinear dynamic characteristics of a nonlocal two-phase piezo-magnetic beam based on a refined higher-order beam formulation and piezoelectric reinforcement scheme. The piezoelectric reinforcement can cause an enhanced vibration behavior of smart nanobeams under magnetic field. Nonlinear governing equations of a smart nanobeam are derived based on refined beam theory, and a numerical trend is provided to obtained nonlinear vibration frequency. This research shows that changing the volume fraction of piezoelectric phase in the material has a great influence on vibration behavior of smart nanobeam under electric and magnetic fields. Also, it can be seen that nonlinear vibration behavior of smart nanobeam is dependent on the magnitude of exerted electric voltage, magnetic potential, hardening elastic foundation and shear deformation.

Thermally Stable Poly(vinylidene fluoride) for High-Performance Printable Piezoelectric Devices.

Piezoelectric polymers, such as poly(vinylidene fluoride) (PVDF) and its copolymers, can achieve large strains and high work density under external electrical fields. These materials are highly desirable in the development of electronic devices and intelligent structures. Here, we demonstrate that dehydrofluorination (DHF) can provide a versatile chemical modification of the PVDF homopolymer that yields thermally stable ferroelectricity. The DHF process significantly increases the fraction of planar chain conformation in the PVDF and results in higher piezoelectric coupling with a wider processing temperature range, compared to traditionally processed PVDF. The efficacy of DHF in promoting planar chain conformation is demonstrated through molecular simulation and further proven by experimental characterization. The induced piezoelectric phases by DHF were able to be preserved through high temperature treatments up to 200 °C. The dehydrofluorinated PVDF exhibits improved electromechanical coupling with a high piezoelectric strain coefficient of d31 = 25.12 ± 1.13 pC/N, which can be further improved to 35.12 ± 0.69 pC/N by common mechanical drawing. This high piezoelectric voltage coefficient leads to an excellent actuation and energy harvesting behavior with a power density of 21.96 mW/cm3 in a flexible undrawn PVDF energy harvester, which is 3.13 times higher than conventionally drawn PVDF. The versatile and scalable method for preparing PVDF polymers with high piezoelectric coupling will enable new manufacturing processes not currently compatible with PVDF homopolymers.

Magneto-electric effects on nonlocal nonlinear dynamic characteristics of imperfect multi-phase magneto-electro-elastic beams

This paper studies nonlinear dynamic characteristics of a nonlocal two-phase piezo-magnetic beam including geometric imperfections by considering piezoelectric reinforcement scheme. The piezoelectric reinforcement can cause an enhanced vibration behavior of smart nanobeams under magnetic field. All of prior papers on piezo-magnetic nanobeams ignore the influence of geometric imperfections which are substantial because a nanobeam is not ever ideal. Nonlinear governing equations of a smart nanobeam are derived based on refined beam theory and a numerical trend is provided to obtained nonlinear vibration frequency. This research shows that changing the volume fraction of piezoelectric phase in the material has a great influence on vibration behavior of smart nanobeam under electric and magnetic fields. Also, it can be seen that nonlinear vibration behavior of smart nanobeam is dependent on the magnitude of exerted electric voltage, magnetic potential, hardening elastic foundation and geometrical imperfection.

Engineering Resonance Modes for Enhanced Magnetoelectric Coupling in Bilayer Laminate Composites for Energy Harvesting Applications

The magnetoelectric (ME) effect in composites, a strain-mediated coupling phenomenon between piezoelectric and magnetostrictive phases, has a wide range of technological applications. Here, ME coupling phenomena are explored in $\mathrm{Pb}$-free piezoelectric, $0.5\mathrm{Ba}({\mathrm{Zr}}_{0.2}{\mathrm{Ti}}_{0.8}){\mathrm{O}}_{3}\text{\ensuremath{-}}0.5({\mathrm{Ba}}_{0.7}{\mathrm{Ca}}_{0.3}){\mathrm{Ti}\mathrm{O}}_{3}$ and piezomagnetic ${\mathrm{Ni}\mathrm{Fe}}_{2}{\mathrm{O}}_{4}$ bilayer laminate composites. The direct and converse ME coupling strengths are found to be enhanced at the electromechanical resonance modes, rather than at the off-resonance frequencies. Here, it is proposed to further enhance the ME coupling strength at electromechanical resonance modes by the in-phase superimposition of the radial and second bending modes via varying the bilayer thickness, which, in turn, varies the volume fraction of the bilayer. The proposed enhanced ME coupling is experimentally demonstrated at a theoretically envisaged bilayer thickness of about 1.8 mm. This results in a large direct ME coupling coefficient of $22.5\phantom{\rule{0.1em}{0ex}}\mathrm{V}\phantom{\rule{0.1em}{0ex}}\mathrm{c}{\mathrm{m}}^{\ensuremath{-}1}\phantom{\rule{0.1em}{0ex}}\mathrm{O}{\mathrm{e}}^{\ensuremath{-}1}$, which is around 100% more than the values observed at individual resonance modes. The results are further validated by calculations from theoretical models. The method adopted in this work gives a roadmap to the significant enhancement of the ME effect in laminate composites.

Degradation behaviour of non-sintered graphene/barium titanate/magnesium phosphate cement bio-piezoelectric composites

A sintering-free magnesium phosphate cement (MPC) with an arbitrary shape is potentially used as a bone implant material, especially with complex shapes. However, the high degradation rate of MPC may lead to the degradation of mechanical properties. In this study, graphene (G)/barium titanate (BT)/MPC composites were fabricated by introducing the piezoelectric phase BT and conductive phase G into MPC, which exhibited the piezoelectric effect after polarisation. The negative surface of the composite may attract Ca2+ and Mg2+ to mineralise rapidly, thereby reducing and improving its degradation rate and mechanical properties, respectively. The contents of additional G and BT were optimised. When BT and G contents were 50 mol% and 0.5 wt%, respectively, the piezoelectric coefficient of the composites increased to 6.31 pC/N, which is an increase of 421% without the addition of G. The results of in vitro degradation and mineralisation in simulated body fluids (SBF) showed that introducing BT and G could effectively slow down the degradation rate, promote mineralisation on the composite surface, and enhance the impact on bone integration.

Temperature-dependent dynamic response in epoxy-free and epoxy-bonded ME composite: a comparative study

This work presents an experimental comparative study of the frequency-dependent response of the epoxy-free magnetoelectric (ME) composite against epoxy-bonded two-phase and three-phase ME composites of various configurations at varying operating temperatures. Conventionally, ME composites are prepared by bonding the piezoelectric and magnetostrictive material phases by means of an epoxy material. Therefore, the response of the composite becomes a function of the properties of the epoxy used. Since the epoxy properties degrade significantly with increase in temperature, the ME response of the ME composite becomes poor at elevated temperatures. In this work, two-phase and three-phase epoxy-free ME composite has been fabricated by employing a press-fit embedded structure and compared with similar epoxy-bonded embedded structure as well as conventional layered ME composite. Frequency-dependent experiments have been conducted at various temperatures and the responses from the two types of composites have been compared. Magnetostriction measurements at different temperatures have been conducted on individual magnetostrictive constituents to observe the effect of piezomagnetic coefficient on the ME response. It is observed that the ME responses of the epoxy-free composites at room temperature are nearly equivalent to their epoxy-bonded counterparts, whereas at higher temperatures the epoxy-free ring composite offers a much better response. The effect of demagnetizing field on the response of composites of various configurations is studied at different temperatures and a similar result is obtained. The resonant frequency of the ME composite is seen to decrease with an increase in temperature owing to the decrease in the effective Young’s modulus of the composite.

Active control for ratios of strains in functionally graded piezoelectric composites

Poisson’s ratio measured by the ratio of transverse strain to longitudinal strain is an important intrinsic property of materials. Imitating the definition of Poisson’s ratio, we define that the ratio of strains is denoted by the ratio of any two normal strains. Nowadays, some design methods have been proposed to tailor the ratios of strains by changing Poisson’s ratio in materials. However, the ranges of the ratios of strains by available methods are too narrow, the technology can provide materials with tailorable ratios of strains over an extremely wide range is rarely studied. To this end, we propose that the ratios of strains in piezoelectric composites can be active-controlled by simultaneously tailoring force and electric fields. The analytical solutions for different ratios of strains in piezoelectric composites subjected to force and electric fields are presented. It is demonstrated that the range of tunable ratios of strains can be from giant negative to giant positive. Moreover, the ratios of strains in any location of FG piezoelectric composites can be greatly affected by force field, electric field, polarization direction, volume fraction of piezoelectric phase. The present study may open up a new routine to design materials possessing extraordinary and programmable mechanical behaviors.

Magnetoelectricity of barium titanate/cobalt ferrite nanoparticles incorporated into poly(vinylidene fluoride-co-trifluoroethylene) copolymer films

Incorporating ferroelectric and ferromagnetic nanoparticles into copolymers can produce composites with novel properties for broad applications especially in electronics. In this research, nanoparticles of barium titanate (BTO) and cobalt iron oxide (CFO) were chemically synthesised and then individually incorporated in poly(vinylidene fluoride-co-trifluoroethylene) to form multi-layered magnetoelectric film. BTO-P(VDF-TrFE)/CFO-P(VDF-TrFE)/BTO-P(VDF-TrFE) sandwich type films - (20-30 μm in thickness each) - were synthesised using a home-made simple mould casting and blending techniques. The addition of BTO and CFO nanoparticles to the polymer enhanced the dielectric constant, but lowered the ferroelectric-paraelectric phase transition temperature of the P(VDF-TrFE). For the sandwich type film, a maximum value of direct out of plane magnetoelectric coupling coefficient (α33) 145 mV/cm·Oe was measured at ambient temperature. For such structure, the perfect isolating condition of the cobalt ferrite piezomagnetic phase and the proper contact and bonding between the piezoelectric and magnetostrictive phases enhanced the magnetoelectric effect. The fabricated film could be a potential candidate for magnetoelectric devices and sensor applications.

Influence of PZT insertion on Portland cement curing process and piezoelectric properties of 0–3 cement-based composites by impedance spectroscopy

0–3 Cement-based piezoelectric composites were produced. It was verified that not only the piezoelectric properties of the composites, but also the influence of piezoelectric phase in the cement paste curing process. The results showed that the final piezoelectric and dielectric properties of the composites depend mainly on the interfacial microstructure between the matrix and the piezoelectric insertion. DC conductivity and impedance spectroscopy measurements showed a high sensitivity to the identification of retard hydration process or phase transformations. Piezoelectric properties show ageing fluctuations, attributed to the cement curing process which promoted unstable dipoles at the same time that it promoted piezoelectric phase constriction.