Shear Piezoelectric Coefficient Research Articles

A biodegradable ZnFe2O4/PLLA electrospun fibers based longitudinal mode piezoelectric membrane for health monitoring

Recently, multifunctional sensors based on piezoelectric active film fabricated with environmental friendly materials is a nascent field which can address the growing concern of electronic waste. Nevertheless, frequently utilized poly(vinylidene fluoride) (PVDF) and poly(L-lactic acid) (PLLA) encounter challenges of limited biocompatibility and weak piezoelectricity with low shear piezoelectric coefficient (d14), respectively. Accordingly, a biodegradable piezoelectric sensor comprising of PLLA nanofiber blended with ZnFe2O4 nanoparticles was developed in this work. The ZnFe2O4 nanoparticles served as heterogeneous nucleation center leading to improved piezoelectric coefficient and output than pure PLLA due to more consistent orientation of CO dipoles. The ZnFe2O4/PLLA film exhibited significant performance improvement featured with 1.7-fold higher longitudinal piezoelectric coefficient (d33 ∼ 6.5 ± 0.3 pm/V), nearly 250 % boosting on the output voltage. The ZnFe2O4/PLLA piezoelectric sensor induced high sensitivity (2–10 N:0.55 V/N; 10–32 N:0.29 V/N) and excellent mechanical stability for 27,000 cycles. The results of the soil burial experiment demonstrate that the film can degrade by over 75 % within 90 days, confirming its excellent biodegradability. Moreover, the ZnFe2O4/PLLA nanofibers based piezoelectric sensor could serve as effective detection evidenced by different output signals of head motion, pulse and artery beating demonstrating its feasible application for health monitoring. Considering the characteristics of straightforward fabrication and readily accessible sustainable materials, the ZnFe2O4/PLLA sensor provides an appealing eco-friendly solution for self-powered flexible personal devices disregarding the need to dispose of electronic waste.

Conformable Shear Mode Transducers from Lead‐Free Piezoelectric Ceramic Coatings: An Innovative Ultrasonic Solution for Submerged Structural Health Monitoring

AbstractShear mode‐guided ultrasonic waves are highly regarded for submerged or subterranean structural health monitoring (SHM), owing to their non‐dispersive feature and minimized acoustic energy loss when in contact with liquid or solid. High‐performance shear mode ceramic ultrasonic transducers with robustness and cost‐effectiveness are highly demanded for underwater or underground SHM applications, especially in harsh environments. However, the implementation of discrete shear mode piezoelectric ceramic ultrasonic transducers is hindered by the inconsistency with manual installation, lack of conformability on curved surfaces, and unreliable acoustic coupling between the transducers and the structure. Here, direct‐write conformable shear mode ultrasonic transducers made from piezoelectric lead‐free ceramic coatings, which are in situ produced on steel structures by a scalable thermal spray process, are proposed. The obtained lead‐free lithium‐doped potassium sodium niobate (KNN‐LN) ceramic coatings exhibit a high effective shear piezoelectric strain coefficient (d24, f) above 60 pm V−1 in a broad frequency range from 100 Hz to 200 kHz. The resulting conformable shear mode KNN‐LN ceramic coating transducers successfully showcase the functions of exciting and detecting stable shear mode ultrasonic wave signals with operation temperature exceeding 200 °C and demonstrate reliable capability in defect detection in both air and liquid environments.

Unravelling the nanoscale mechanism of polarization reversal in a Hf0.5Zr0.5O2-based ferroelectric capacitor by vector piezoresponse force microscopy.

Ferroelectricity is in demand in many device concepts in electronics, energy and microsystem engineering. The performance of ferroelectrics-based devices is determined by either out-of-plane or in-plane polarization, or out-of-plane or in-plane piezoelectric strain. Real prospects for the practical implementation of innovative devices opened up after the discovery of ferroelectricity in ultrathin hafnium oxide films, due to their perfect compatibility with silicon technology. Ferroelectric properties of this material have been assigned to an orthorhombic structural phase with a single polar axis, but the spatial orientation of the polarization vector and the tensorial piezoelectric behaviour, which are inextricably coupled, still remain unknown. Herein, the rotation of the polarization vector in a Hf0.5Zr0.5O2 (10 nm) capacitor during polarization switching and the spatial distribution of longitudinal and shear piezoelectric coefficients are elucidated at the nanoscale using operando vector piezoresponse force microscopy. In most of the capacitor, a 180°-flipping of the polarization vector is observed, which is consistent with the orthorhombic phase structure. However, a rather large fraction of the capacitor is also occupied by nanoregions of ferroelastic (non-180°) switching, which is explained by the effect of the local mechanical stress. To quantify the three-dimensional piezoresponse, a novel approach exploiting the Poisson effect in artificially created non-ferroelectric regions is proposed and it shows that the shear piezoelectric coefficient is twice the longitudinal coefficient. The experimental insights entail an important step in fundamental understanding of the ferroelectric and piezoelectric properties of hafnium oxide and have great potential to trigger new versions of ferroelectric-based devices.

Energy harvesting by uniaxially-stretched poly(lactide) films at low tensile strain frequencies for powering wearable sensors: experimental results and theoretical extrapolation

Poly(lactide) (PLA) is an eco-friendly and low-cost polymer with a shear piezoelectricity easily induced by uniaxial stretching and without poling process. These interesting features make PLA as a good candidate to replace the widely-used poly(vinylidene difluoride) (PVDF) piezoelectric polymer, in particular for flexible energy harvesting applications aiming to power wearable sensors. In this work, PLA films were fabricated by a simple extrusion–orientation process. The energy harvesting efficiency of the PLA films were characterized using a custom-built test bench designed for flexible piezoelectric materials and working in tensile mode at low strain frequencies. The measurements on PLA films show a maximal output power about 3.7 μW harvested by applying a strain of 1% at 20 Hz. A theoretical model was developed based on electromechanical parameters to ascertain the energy harvesting performances of PLA. The validated model was also helpful to estimate the output power from PLA films by increasing their active surface areas and/or improving their shear piezoelectric coefficients (d 14). The optimized PLA film could produce an output power comparable to that produced by PVDF film in the same mechanical excitation conditions. This study consequently highlights the potential of PLA for energy harvesting applications and the utility of the developed model to estimate the electrical power generated by piezoelectric polymers.

Piezoelectric Response of Plastic Ionic Molecular Crystals: Role of Molecular Rotation

Plastic ionic molecular crystals are a novel class of materials that have attracted recent interest due to the discovery of ferroelectric and piezoelectric properties together with an orientationally disordered mesophase with high plasticity. Despite the growing interest, little is known about the mechanisms that underpin their piezoelectric properties. To address this knowledge gap, we use density functional theory calculations with van der Waals density functionals to study the dielectric, piezoelectric, and elastic properties of 11 plastic ionic molecular crystals. The piezoelectric coefficients were found to reach values comparable to inorganic piezoelectrics. Further, some plastic crystals have strikingly large piezoelectric anisotropies. For HQReO4 (quinuclidinium perrhenate) an anisotropy of |d16/d33| = 118 was found, 11 times that of LiNbO3, a phase pure inorganic noted for its anisotropy. Our study links the anisotropy to the rotational motion of the constituent molecules in response to shear stress. The large shear piezoelectric coefficients, yet modest dielectric permittivity, results in coupling coefficients─a measure of its suitability for energy harvesting─with values up to 0.79. Our study points to the engineering of the rotational response of plastic ionic crystals as key to realizing the outstanding functional properties of these compounds.

Origin of high piezoelectricity of a bismuth-based organic–inorganic hybrid crystal

A bismuth-based organic–inorganic hybrid single crystal with a chiral nature is constructed, which has a large shear piezoelectric coefficient of 46.54 pC N−1 with an electromechanical coupling coefficient over 40%.

Evaluation of shear piezoelectric coefficients by a bimorph cantilever technique for extruded and oriented poly(l‐lactide) films

AbstractUniaxially stretched poly(l‐lactide) (US‐PLA) films display shear piezoelectric properties of interests for smart applications. However, the measurement of these properties is quite challenging and a simple technique based on bimorph cantilevers is here used. This technique is validated with commercial piezoelectric poly(vinylidene fluoride) (PVDF) films. A piezoelectric coefficient d31 close to 19 pm/V is then obtained with a precision close to 5% and a good accuracy to expected values. For US‐PLA films made by extrusion—machine‐direction orientation, shear piezoelectric coefficients d14 up to 5.9 pm/V are found. Relevant trends can be captured but a low precision on d14, close to 10%, is highlighted. This behavior is probably related to film thickness heterogeneities arising from the extrusion processing at the laboratory scale. Piezoelectric voltage coefficients (g14) and electromechanical coupling coefficients could be also easily obtained with additional measurements of the dielectric permittivity and mechanical compliance. Outstanding g14 coefficients up to 320 mV.m/N are confirmed for US‐PLA films with a precision close to 20%. The bimorph cantilever technique consequently represents a simple and reliable technique to evaluate piezoelectric properties of soft materials, in particular shear piezoelectric properties of US‐PLA films for future developments and optimizations at the pilot scale.

Performance improvement of micro-ultrasonic motors using the thickness shear mode piezoelectric elements

We propose a one-millimeter-scale traveling-wave ultrasonic motor that uses a thickness shear mode (15-mode) piezoelectric elements with a high shear piezoelectric coefficient. This thickness shear mode makes the micromotor suitable for operating with higher energy efficiency than conventional micromotors and enables a low voltage operation and a high torque generation. In this study, we build a thickness shear mode-driven micro-ultrasonic motor and demonstrate the improvement in motor performance. A micromotor comprising a cube with a side length of 1 mm and four piezoelectric plates is fabricated, and its dynamic and static characteristics are evaluated experimentally. With an optimal preload mechanism, the micromotor obtains unprecedented performance measures: an efficiency of 2.1% and a torque of 40 µNm, which are 3–4 times larger than those of a comparable micromotor using typical expansion mode (31-mode) piezoelectric elements. Currently, the proposed motor is the most powerful micromotor in 1–2 millimeter-scale actuators and represents a new benchmark for micromotors.

Parameter Identification of the Nonlinear Piezoelectric Shear d15 Coefficient of a Smart Composite Actuator

The objective of this work is to characterize the nonlinear dependence of the piezoelectric d15 shear coefficient of a composite actuator on the static electric field and include this effect in finite element (FE) simulations. The Levenberg-Marquardt nonlinear least squares optimization algorithm implemented in MATLAB was applied to acquire the piezoelectric shear coefficient parameters. The nonlinear piezoelectric d15 shear constant of the composite actuator integrated with piezoceramic d15 patches was obtained to be 732 pC/N at 198 V. The experimental benchmark was simulated using a three-dimensional piezoelectric FE model by taking piezoelectric nonlinearity into consideration. The results revealed that the piezoelectric shear d15 coefficient increased nonlinearly under static applied electric fields over 0.5 kV/cm. A comparison between the generated transverse deflections of the linear and nonlinear FE models was also performed.

Effective properties of piezoceramics with metal inclusions: numerical analysis

The paper considers the problem of determining the effective properties of piezoceramics with metal inclusions. The homogenization problem was numerically solved in the representative volume with closed structure of inclusions. The effective moduli behavior was analyzed depending on the fraction of inclusions for piezoceramic PZT-5A with platinum inclusions. An increase in the effective stiffness moduli, the longitudinal and shear piezoelectric stress coefficients, and a considerable increase in the dielectric permittivities were discovered with the growth of the metal inclusions fraction. The effective dielectric permittivities grew for the same fraction of inclusions when the relative size of inclusions increased.

Ferroelastic-switching-driven large shear strain and piezoelectricity in a hybrid ferroelectric.

Materials that can produce large controllable strains are widely used in shape memory devices, actuators and sensors1,2, and great efforts have been made to improve the strain output3-6. Among them, ferroelastic transitions underpin giant reversible strains in electrically driven ferroelectrics or piezoelectrics and thermally or magnetically driven shape memory alloys7,8. However, large-strain ferroelastic switching in conventional ferroelectrics is very challenging, while magnetic and thermal controls are not desirable for practical applications. Here we demonstrate a large shear strain of up to 21.5% in a hybrid ferroelectric, C6H5N(CH3)3CdCl3, which is two orders of magnitude greater than that in conventional ferroelectric polymers and oxides. It is achieved by inorganic bond switching and facilitated by structural confinement of the large organic moieties, which prevents undesired 180° polarization switching. Furthermore, Br substitution can soften the bonds, allowing a sizable shear piezoelectric coefficient (d35 ≈ 4,830 pm V-1) at the Br-rich end of the solid solution, C6H5N(CH3)3CdBr3xCl3(1-x). The electromechanical properties of these compounds suggest their potential in lightweight and high-energy-density devices, and the strategy described here could inspire the development of next-generation piezoelectrics and electroactive materials based on hybrid ferroelectrics.

Piezoelectric Heterogeneity in Collagen Type I Fibrils Quantitatively Characterized by Piezoresponse Force Microscopy.

Piezoelectricity of Type I collagen can provide the stress-generated potential that is considered to be one of the candidate mechanisms to explain bone's adaptation to loading. However, it is still challenging to quantify piezoelectricity because of its heterogeneity and small magnitude. In this study, resonance-enhanced piezoresponse force microscopy (PFM) was utilized to amplify a weak piezoresponse of a single collagen fibril with a carefully calibrated cantilever. The quantitative PFM, combined with a dual-frequency resonance-tracking method, successfully identified the anisotropic and heterogenous nature of the piezoelectric properties in the collagen fibril. The profile of shear piezoelectric coefficient (d15) was obtained to be periodic along the collagen fibril, with a larger value in the gap zone (0.51 pm/V) compared to the value in the overlap zone (0.29 pm/V). Interestingly, this piezoelectric profile corresponds to the periodic profile of mechanical stiffness in a mineralized collagen fibril having a higher stiffness in the gap zone. Considering that apatite crystals are nucleated at the gap zone and subsequently grown along the collagen fibril, the heterogeneous and anisotropic nature of piezoelectric properties highlights the physiological importance of the collagen piezoelectricity in bone mineralization.

Effect of carbon doping on electromechanical response of boron nitride nanosheets

The electromechanical response of hexagonal-boron nitride nanosheets (h-BNSs) was studied via molecular dynamics simulations (MDS) with a three-body Tersoff potential force field using a charge-dipole (C-D) potential model. Carbon (C)-doped h-BNSs with triangular, trapezoidal and circular pores were considered. The elastic and piezoelectric coefficients of h-BNSs under tension and shear loading conditions were determined. The induced polarization in h-BNSs was found to depend on the local arrangement of C atoms around B and N atoms, and the polarization increases if C atoms are surrounded by N atoms. This is attributed to the generation of higher dipole moments due to C–N bonds compared with C–B bonds. At ∼5.5% C-doping concentration, the axial piezoelectric coefficient of doped h-BNSs with triangular and trapezoidal pores increased by 18.5% and 3.5%, respectively, while it reduced by 22.5% in the case of circular pores compared to pristine h-BNS. The shear piezoelectric coefficient of C-doped h-BNSs with triangular and trapezoidal pores increased by 20.5% and 1%, respectively, while it reduced by 7% in case of circular pores. Young’s moduli of C-doped h-BNSs with triangular, trapezoidal and circular pores increased by 9%, 7.5% and 5.5%, respectively, due to the C–C bonds being stronger than all other bonds. The respective improvements in shear moduli are 8.5%, 5% and 5%. The elastic and piezoelectric properties of armchair h-BNSs were found to be higher than zigzag h-BNSs. The results also reveal that the piezoelectric coefficient increases as doping increases; it reaches its maximum value around 0.41 C m−2 at 12.6% C-doping concentration and then starts decreasing. The present work shows that we can engineer the electromechanical response of h-BNSs via novel pathways such as different types and size of pores as well as C-doping concentration to suit a particular nanoelectromechanical systems (NEMS) application.

Broadband bimorph piezoelectric energy harvesting by exploiting bending-torsion of L-shaped structure

Vibration-based piezoelectric energy harvesting has the potential to effectively power electronic sensors and communication devices of wireless networks. To address the need to increase the levels of harvested energy and increase its frequency bandwidth, we exploit multi-modal and multi-directional responses of a simple structure. Given advances made in developing piezoelectric materials with large face shear piezoelectric coefficients (d36), we explore the potential of developing a broadband and highly efficient bending-torsion L-shaped bimorph harvester through exploiting the d31 and d36 modes. A distributed-parameter model based on the Euler-Bernoulli beam assumptions is developed to assess the efficiency and power density of the proposed harvester. The model is validated with experiments and finite element simulations. The influence of the excitation angle as well as key geometric parameters of the L-shaped harvester on the energy harvesting efficiency and voltage frequency-response curve are presented and analyzed. The results show that the proposed structure and approach improves the frequency bandwidth with a frequency response that covers the first three modes of the harvester. The harvester yields an average power of 1.790 μW over a frequency range between 20 and 200 Hz, which is larger than bending mode L-shaped harvester (0.825 μW), cantilever harvester with the same length of main beam (0.764 μW) and auxiliary beam (1.037 μW). The investigated L-shaped structure constitutes a promising harvester that supports multi-directional and multi-mode energy harvesting.

The tunable ferroelectricity and piezoelectricity of the KNN piezoceramics by Na concentrations: First-principles calculations

The ferroelectric and piezoelectric properties of orthorhombic K1-xNaxNbO3 (KNN) piezoceramics with various Na concentrations x are studied by the first-principles calculations. The spontaneous polarization of KNN single crystals increases monotonically with Na concentrations, indicating an enhanced ferroelectricity in KNN. Moreover, the averaged shear, transverse and longitudinal piezoelectric coefficient d-15*, d-31* and d-33* of KNN piezoceramics are calculated from the data of KNN single crystals to show that piezoelectricity of KNN piezoceramics positively correlates with Na concentrations and exhibits the best performance at x = 0.5625, which agrees well with the available experimental data. At this concentration, d-15*, d-31* and d-33* of orthorhombic KNN piezoceramics reach maximum, which are 1.13, 1.79 and 0.85 times larger than those of KNbO3 piezoceramics, respectively. This work provides a better understanding to the effect of Na concentrations on the enhanced ferroelectricity and piezoelectricity in the KNN piezoceramics.

Crystal Structure and Strong Piezoelectricity of New Amino Acid Based Hybrid Crystals: [H-β-(3-Pyridyl)-Ala-OH][ClO4] and [H-β-(4-Pyridyl)-Ala-OH][ClO4

The new amino acid based [H-β-(3-pyridyl)-Ala-OH][ClO4] and [H-β-(4-pyridyl)-Ala-OH][ClO4] crystals were synthesized, and their structure and functional piezoelectric properties were investigated in detail. Both analogs crystallize in the polar, piezoelectric P21 space group. Piezoresponse force microscopy (PFM) measurements revealed that shear piezoelectric coefficient of [H-β-(3-Pyridyl)-Ala-OH][ClO4] crystal is more than twice that in the widely used transducer material lithium niobate, LiNbO3. The crystal structures of both perchlorate derivatives were determined, and the influence of the inter- and intramolecular hydrogen bond network on piezoelectricity of crystals were discussed. The existence of the intramolecular hydrogen bonding was confirmed by means of IR spectroscopy measurements. Thermogravimetric (TGA) technique was applied to study the thermal behavior of title crystals.

Piezoelectric energy harvester for pacemaker application: a comparative study

This study proposes the cantilever design of piezoelectric energy harvester scavenging energy from blood pressure variation in cardiac cycle. The harvester could be a perennial source of power for a typical pacemaker. The concept of three cm long and 72 μm thin cantilever based energy harvester having natural frequency close to that of heartbeat has been proposed. Considering a huge difference between shear (d15) and transverse (d31) piezoelectric coefficient the harvester was operated in two different modes. A number of materials (single and polycrystalline ceramics) along with Pb[ZrxTi1−x]O3 (PZT-5A) were operated in transverse and shear modes. The maximum open circuit voltage found for all cases was ∼6 V which was yielded by Pb(Zn1/3Nb2/3)O3–(6–7)% PbTiO3 (PZN-PT) when operating in shear mode. Further, the optimum resistance was calculated for all the materials under study operating in d15 and d31 modes for a wide frequency range. It was found that the maximum power among all materials under study was given by PZN-PT which is ∼13 μW while operating in shear mode. Such high magnitude of power harvested is due to its giant d15 which is 6000 pC N−1 and is sufficient to power a typical pacemaker.

Effect of the Chloride Anions on the Formation of Self-Assembled Diphenylalanine Peptide Nanotubes.

Self-assembled peptide nanostructures are being intensively investigated due to their potential applications such as biosensors, piezotransducers, and microactuators. It was predicted that their formation and hence piezoelectric property strongly depend on the water content and acidity of the stock solution. In this paper, simple diphenylalanine (FF) tubular structures were fabricated from the solutions with added hydrochloric acid in order to understand the influence of chloride ions on the self-assembly process and resulting piezoelectricity. Low-frequency Raman scattering, atomic, and piezoresponse force microscopies were used to characterize both the morphology and piezoelectric properties of the grown samples. The mechanism of chloride anions' effect on the formation of self-assembled peptide nanostructures is discussed based on the acquired Raman data and quantum-chemical modeling. It is shown that the addition of chloride anions causes a significant reduction of the dipole moments of FF tubes accompanied with the concomitant decrease of tube dimensions and apparent shear piezoelectric coefficients.

Single crystal growth and temperature dependent behaviors of melilite type piezoelectric crystal Ca2Al2SiO7

High temperature piezoelectric crystals are desired for sensing at elevated temperatures. In this work, a large size (2 in.) and low cost Ca2Al2SiO7 (CAS) crystal was grown by using the Czochralski pulling method. Thermal expansion coefficients α11 and α33 were measured and found to be on the order of 5.70 × 10−6/°C and 10.12 × 10−6/°C, respectively. The electrical resistivities of the CAS crystal along the X- and Z-directions at 700 °C were found to be 3 × 107 and 2 × 108 Ω·cm, respectively. The electro-elastic constants were evaluated by using the impedance and pulse-echo methods, where the piezoelectric coefficients d14 and d36 were determined to be 6.7 and 2.8 pC/N at room temperature, respectively. Moreover, the temperature dependence of the electro-elastic properties of the CAS crystal was investigated. The variation of elastic compliances was found to be <6% over the tested temperature range of 20–700 °C. The optimum crystal cuts with the maximum longitudinal and thickness shear piezoelectric coefficients for the CAS crystal were predicted, where the largest longitudinal piezoelectric d11∗ (3.1 pC/N) was achieved for the (XYtl)45°/−55° crystal cut, and the largest shear piezoelectric d26∗ (4.7 pC/N) was found for the (YXl)45° crystal cut, nearly two times that of α-quartz.

Magnetoelectric effect in stretch-shear mode self-biased LiNbO3 based composite with high-frequency resonant response

Magnetoelectric (ME) composites have received attention abidingly due to the promising potential applications in magnetic field sensor and energy harvester. In recent years, shear mode ME composite was frequently discussed with promising applications in high-frequency magnetic field with large signal-to-noise ratio. Single-crystal LiNbO3, as a lead-free piezoelectric phase with high mechanical quality factor and small dielectric constant, is suitable for achieving a large shear ME effect with large shear piezoelectric coefficient d15 or d24, and different piezoelectric coefficients can be obtained by crystal-cut transformation. The transformation rule of shear ME coefficient with transformation of LiNbO3 crystal orientation and the MHz high-frequency magnetic detection is still lacking. Furthermore, self-biased ME composite can be obtained with SrFe12O19 ribbon, which is useful for the integration and miniaturization of ME sensor. In the present work, we use a series of X-cut LiNbO3 to obtain different d15 or d16 in a stretch-shear ME composite. Piezoelectric coefficient d15 and ME coefficient E15 of Metglas/LiNbO3 composite are obtained in experiment, respectively. The results show that LiNbO3 xzt/30 has the largest d15 and E15, and the transformation rule of E15 is consistent with the coordinate transformation of d15. The structure of stretch-shear ME composite is optimized to improve the ME coefficient. Then the stretch-shear mode self-biased SrFe12O19/Metglas/LiNbO3 composite is fabricated, and shear ME response is observed under zero external direct current magnetic bias. Moreover, E15 at electromechanical resonance frequency is gained at shear-mode high frequency (0.991 MHz and 3.51 MHz). The largest ME coefficient E15 is acquired in the stretch-shear 5-foil Metglas/LiNbO3 (xzt/30) composite of 134.16 mV/(cmOe) at 1 kHz and 9.17 V/(cm Oe) at 3.51 MHz. This work is beneficial to the confirming of the corresponding rules of shear ME coefficient and LiNbO3 piezoelectric coefficient, showing that the composite possesses the potential applications in integration, miniaturization and high-frequency resonant sensor.