Piezoelectric Strain Constant Research Articles

AC poling of high Qm and low acoustic impedance Pb(Mg1/3Nb2/3)O3-Pb(Zr,Ti)O3 single crystals produced by a solid-state crystal growth

The AC poling cycle dependence of Mn-doped Pb(Mg1/3Nb2/3)O3-0.3Pb(Zr.Ti)O3 (PMN-0.3PZT) single crystals (SC) produced via the solid-state crystal growth (SSCG) method was investigated. The piezoelectric strain and charge constants, d 33 ＝ 1130 pC/N, g 33 = 42.7 × 10−3 Vm/N, and mechanical quality factor Q m = 800 were obtained under conditions of 1 Hz, bipolar sine wave, 7.5 kV cm−1 electric field, and 6000 cycles. In contrast to the conventional Bridgman process SC, the low-density and high Q m SSCG SC necessitates a substantial number of AC cycles due to the presence of pores within the SC. In addition, the ACP SC showed a 13 °C increase in the phase change temperature T rt compared to the DC-poled SC. This information on ACP SSCG SCs with improved thermal stability, low acoustic impedance, and enhanced receiving efficiency attributable to high g 33 offers new insight into high-frequency ultrasonic devices.

Sol-gel fabrication of transparent ferroelectric (K,Na)NbO3/La0.06Ba0.94SnO3 heterostructure

Lead-free K0.5Na0.5NbO3 (KNN) ferroelectric film and transparent La0.06Ba0.94SnO3 (LBSO) bottom electrode are fabricated on (001)-oriented SrTiO3 (STO) substrate by sol-gel. The characterization results confirm an epitaxial relationship between the films and the substrate, as well as a uniform structure and good crystallization quality of the films. The optical measurement shows that the film heterostructure exhibit a high transmittance with a maximum transmittance of ∼80%. The polarization-electric field (P-E) curves demonstrate that the twice remanent polarization value of the ∼500 nm thick KNN film reaches up to 28 μC/cm2 under an electric field of 800 kV/cm, and the effective piezoelectric strain constant (d33*) is measured as 24.8 pm/V. The dielectric properties of the film are displayed, and the leakage behavior can be divided into three stages of Ohmic conduction, Schottky emission and Poole-Frenkel emission with increasing the applied electric field. This study indicates that transparent lead-free ferroelectric KNN heterostructures can be prepared using a cost-effective sol-gel method and shows promise for future applications.

Preparation of porous lead zirconate titanate piezoelectric ceramics via vat photopolymerization combined with burnt polymer spheres technique

Porosity plays an important factor on the electric properties of piezoelectric ceramics. Here, we propose a promising method for the fabrication of Lead zirconate titanate (PZT) piezoelectric ceramics using vat photopolymerization, and effectively modulate porosity of printed PZT piezoceramics through adjusting the polystyrene (PS) content. After a post-process, the PZT piezoelectric ceramics showed single perovskite structure and porous microstructures formed by PS, with porosity ranging from 8.57 % to 27.02 %. With the increase of porosity, the piezoelectric strain constant (d33) and dielectric permittivity (ɛr) decreased gradually due to the reduction in the volume fraction of PZT phase per unit volume. When the PS content was 20 vol%, d33 and ɛr reached the maximum values. The sintered PZT piezoelectric ceramics exhibited excellent electrical properties (ɛr=2364, d33=399 pC/N, g33=1.91×10−2 Vm/N, d33g33=7.62×10−12 m2/N and Kt=43.94 %). This work not only provides technical support for manufacturing advanced ceramics with tunable porosity through the use of PS powders, but also lays the foundation for preparing functional ceramics with complicated designed structures through vat photopolymerization technology.

Magnetism, ferroelectricity, and piezoelectricity in bulk α-CrOOH and its monolayer

Multifunctional materials with magnetic, piezoelectric, and ferroelectric properties have a wide range of applications. This study investigates the properties of bulk α-CrOOH and its monolayer using density functional theory. The findings reveal that bulk α-CrOOH exhibits a weak interlayer antiferromagnetism, but has a ferroelectric polarization of 28.45 µC/cm2 and piezoelectric strain constants d33 of 21.69 pm/V, which are comparable to those of the multiferroic material BiFeO3. The monolayer of α-CrOOH is a low-temperature ferromagnetic semiconductor that exhibits robust piezoelectricity. This is because of the intrinsic mirror symmetry breaking in the z-direction, resulting in large out-of-plane piezoelectric coefficients of e31 = 31.914 pC/m and d31 = 0.22 pm/V. These intriguing electric and magnetic properties make polarized bulk and monolayer α-CrOOH potential candidates for piezoelectric and ferroelectric device applications.

3D printing of lead zirconate titanate piezoelectric ceramics via digital light processing (DLP)

Research of piezoelectric ceramics via DLP technology has drawn considerable interest due to its high geometrical flexibility. However, the poor curing properties limit the use of DLP technology to fabricate piezoelectric ceramics. Herein, we overcome this challenge in prepared lead zirconate titanate (PZT) piezoelectric ceramics via DLP technology by incorporating ultralow refractive index and ultraviolet light absorptivity of soluble starch in PZT ceramic slurry. After the post-process, the relative density of printed PZT ceramic with 20 vol% soluble starch could reach about 89.51% of theoretical density. The printed PZT ceramic exhibits remarkable dielectric permittivity, remnant polarization, piezoelectric strain constant, piezoelectric voltage constant, figure of merit and electromechanical coupling factor of 2196, 35.56 μC/cm2, 373 pC/N, 1.92 × 10−2 Vm/N, 7.16 × 10−12 m2/N and 42.28%, respectively. The results achieved in this research indicate that our work provides a promising route for fabrication of advanced ceramics with high performance and designed complex structures by digital light processing.

Modulation of Electrical Characteristics of Polymer–Ceramic–Graphene Hybrid Composite for Piezoelectric Energy Harvesting

The use of lead-based ceramics to enhance the piezoelectricity of poly(vinylidene fluoride) (PVDF) is the primary challenge toward nontoxic flexible piezoelectric devices. 0.67BiFeO3-0.33BaTiO3 (BF33BT) is one of the lead-free piezoceramics with high-temperature stability and comparable piezoelectric characteristics to existing lead-based piezoceramics. The work represents PVDF–BF33BT two-phase and PVDF–BF33BT–graphene oxide (GO) three-phase composites with detailed analysis of the dielectric, ferroelectric, and piezoelectric characterizations. Solvent-casting followed by the hot-pressing technique improves the electroactive β-phase of ≥60% in the composites. With BF33BT and GO loading, the dielectric constant and loss tangent increase; however, there is an abrupt rise at the threshold GO concentration of 0.08 wt %. The three-phase composite with 40 wt % BF33BT and 0.08 wt % GO records a dielectric constant of 303 and a loss tangent of 0.68. The harvester out of the same composition achieves a piezoelectric strain constant of 9 pC·N–1, an open-circuit voltage of ∼3.9 V, and a short-circuit current of 1.3 μA. The feasibility of the harvester was tested by powering a calculator by charging a 2.2 μF capacitor after rectification. The recoverable energy density also improves seven times, indicating that the PVDF–BF33BT–GO composite is preferable for piezoelectric and energy storage applications.

Early Performance Evolution Tracking and Monitoring for Cement-based Piezoelectric Composites under Multiple Curing Conditions

Piezoelectric composites based on 0 – 3 cement have been extensively employed in structural health monitoring. Significantly, curing conditions considerably affect the forming strength of matrix materials. In order to obtain the best molding conditions of 0 – 3 cement-based piezoelectric composites, this paper studied the evolution of various parameters with time during the early molding process of 0 – 3 cement-based piezoelectric composites under different temperature and humidity conditions. The analysis indicated that the higher the temperature, which increases the forming speed of the sample, the lower the curing humidity, which decreases the current generated during the polarisation process of the sample, and longer the time required to attain the polarisation voltage. The test concluded that the curing condition of high temperature and high humidity was conducive to obtaining higher piezoelectric and dielectric properties of the sample and the piezoelectric strain constant and dielectric constant reached the maximum value at 80°C/100RH, which were 45.5 pC/N and 44.36 respectively.

Doping Engineering for Optimizing Piezoelectric and Elastic Performance of AlN

The piezoelectric and elastic properties are critical for the performance of AlN-based 5G RF filters. The improvement of the piezoelectric response in AlN is often accompanied by lattice softening, which compromises the elastic modulus and sound velocities. Optimizing both the piezoelectric and elastic properties simultaneously is both challenging and practically desirable. In this work, 117 X0.125Y0.125Al0.75N compounds were studied with the high-throughput first-principles calculation. B0.125Er0.125Al0.75N, Mg0.125Ti0.125Al0.75N, and Be0.125Ce0.125Al0.75N were found to have both high C33 (>249.592 GPa) and high e33 (>1.869 C/m2). The COMSOL Multiphysics simulation showed that most of the quality factor (Qr) values and the effective coupling coefficient (Keff2) of the resonators made with these three materials were higher than those with Sc0.25AlN with the exception of the Keff2 of Be0.125Ce0.125AlN, which was lower due to the higher permittivity. This result demonstrates that double-element doping of AlN is an effective strategy to enhance the piezoelectric strain constant without softening the lattice. A large e33 can be achieved with doping elements having d-/f- electrons and large internal atomic coordinate changes of du/dε. The doping elements-nitrogen bond with a smaller electronegativity difference (ΔEd) leads to a larger elastic constant C33.

Enhanced piezoelectric strain response in 〈100〉 grain‐oriented lead‐free bismuth ferrite–based piezoelectric ceramics

AbstractThe 〈100〉 grain‐oriented 0.11(Bi0.5K0.5)TiO3–0.23BaTiO3–0.02Bi(Mg0.5Ti0.5)O3–0.64BiFeO3 piezoelectric ceramics were prepared by a reactive templated grain growth method using a platelike H1.08Ti1.73O4·nH2O (HTO) template and Bi2O3–KHCO3–MgO–Fe2O3–BaCO3 matrix particles. The high degree of texturing (a Lotgering orientation factor of 80%) and high density (95%) were achieved by employing weight‐pressing treatment during the binder‐removal and sintering treatment along with optimizing the sintering temperature. The water‐quenching treatment has a significant impact on the enhancement of dielectric, ferroelectric, and piezoelectric properties with the increase of dielectric constant, remanent polarization, and piezoelectric strain constant from 764, 13.6 μC/cm2, and 384 pm/V for the as‐sintered ceramics to 812, 29.9 μC/cm2, and 526 pm/V after the water‐quenching treatment at 850°C, respectively. The obtained piezoelectric strain constant with a 1.8 times enhancement compared to that of the ceramics with randomly oriented grains is significantly higher than those reported for other lead‐free piezoelectric ceramics with Curie temperature >300°C. This study suggested the strong potentiality of this material system for high‐temperature actuator application.

Design and Fabrication of 15-MHz Ultrasonic Transducers Based on a Textured Pb(Mg1/3Nb2/3)O3-Pb(Zr, Ti)O3 Ceramic.

Ultrasound medical imaging is an entrenched and powerful tool for medical diagnosis. Image quality in ultrasound is mainly dependent on performance of piezoelectric transducer elements, which is further related to the electromechanical performance of the constituent piezoelectric materials. With rising need for piezoelectric materials with better performance and low cost, a highly 〈001〉 textured piezo ceramic, Pb(Mg1/3Nb2/3)O3-Pb(Zr, Ti)O3, has been developed. Recently, textured ceramic materials can be produced at low cost and exhibit high piezoelectric strain constants and large electromechanical coupling coefficients. In this work, 15-MHz ultrasonic transducers with an effective aperture of 2.5 mm in diameter based on these highly 〈001〉 textured ceramics have been successfully fabricated. The fabricated transducers achieved a central frequency of 15 MHz, a fractional bandwidth of 67% (at -6 dB), a high effective electromechanical coupling coefficient [Formula: see text] of 0.55, and a low insertion loss (IL) of 21 dB. Ex vivo ultrasonic imaging of a porcine eyeball was used to assess the tomography quality of the transducer. The results show that utilized textured ceramic has a great potential in developing ultrasonic devices for biomedical imaging purposes.

Bond engineering of molecular ferroelectrics renders soft and high-performance piezoelectric energy harvesting materials

Piezoelectric materials convert mechanical stress to electrical energy and thus are widely used in energy harvesting and wearable devices. However, in the piezoelectric family, there are two pairs of properties that improving one of them will generally compromises the other, which limits their applications. The first pair is piezoelectric strain and voltage constant, and the second is piezoelectric performance and mechanical softness. Here, we report a molecular bond weakening strategy to mitigate these issues in organic-inorganic hybrid piezoelectrics. By introduction of large-size halide elements, the metal-halide bonds can be effectively weakened, leading to a softening effect on bond strength and reduction in polarization switching barrier. The obtained solid solution C6H5N(CH3)3CdBr2Cl0.75I0.25 exhibits excellent piezoelectric constants (d33 = 367 pm/V, g33 = 3595 × 10−3 Vm/N), energy harvesting property (power density is 11 W/m2), and superior mechanical softness (0.8 GPa), promising this hybrid as high-performance soft piezoelectrics.

3D printed 0–3 type piezoelectric composites with high voltage sensitivity

Piezoelectric composites made of piezoelectric ceramic particles and polymer composites combine the performance advantages of both components and have broad application prospects. However, the preparation of complex structures is still a challenge, for which 3D printing technology provides a perfect solution. The aim of the present study is to investigate the principle and process optimization of the stereolithography of 0–3 type piezoelectric composites through simulation and experiments. In particular, a modified three-phase model of a spherical shell is applied to elucidate the influence of the elastic modulus between the ceramic particles and the matrix on the piezoelectric properties of the composites at the macroscopic level. This enables the piezoelectric properties of the composites to be predicted more accurately, and guides the surface grafting modification of piezoelectric ceramic powders. Furthermore, the problem of weak interface bonding in piezoelectric composites caused by poor compatibility between hydrophilic particles and the hydrophobic matrix is successfully solved by preprocessing the PZT ceramic powder via activating the particle surface hydroxyl groups and grafting a silane coupling agent onto the piezoelectric ceramic powder. As a result, the particles are bonded to the matrix by covalent bonds, which increases the elastic modulus of the interface transition layer and modifies the stress transfer efficiency. For instance, the piezoelectric strain constant (d33) of piezoelectric composite containing 60 wt% functionalized PZT particles is increased from 20 to 37 pC/N. The printing accuracy, piezoelectric properties, and mechanical characteristics of the piezoelectric composites are thoroughly investigated, and the reliability of the proposed theoretical model and simulation results is verified. The piezoelectric composites are uniformly compact and have a low residual pore rate. The piezoelectric composite with a solid content of 60 wt% has a volume density of 2.27 g/cm3 and a Young's modulus of 535.44 MPa. Most importantly, its piezoelectric voltage constant (g33) is 167.2 × 10−3 Vm/N, which is more than seven times higher than that of homogeneous PZT and results in high voltage sensitivity.

Phase evolution and <110>‐orientation mechanism in RTGG‐processed BaTiO3 ceramics with electrical properties

AbstractThe <110>‐oriented BaTiO3 ceramics were fabricated using BaCO3 matrix and H1.08Ti1.73O4.nH2O (HTO) template particles, and the mechanism of BaTiO3 phase formation was investigated. The dielectric, ferroelectric, and piezoelectric properties were also investigated. The transformation of the HTO phase into the TiO2 bronze or TiO2 (B) phase was observed at 600°C, where the BaTiO3 nucleation was accompanied by the formation of a Ba2TiO4 phase. The TiO2 phase reacted with the Ba2TiO4 phase at 800°C to give a BaTiO3 phase, whereas its reaction with the BaTiO3 resulted in the formation of BaTi2O5 phase that got decomposed into BaTiO3 and Ba6Ti17O40 phase at sintering temperature ≥1300°C. Sintering with samples’ embedding in BaTiO3 powders prevented the formation of the Ba6Ti17O40 secondary phase. The crystallographic orientation along the <110> direction (F110) was developed by the epitaxial grain growth mechanism. In addition to the contribution of the grain‐size increment for enhancing the F110, the preservation of the platelike structure was also found to have a significant impact. The ceramics prepared by the embedded sintering (grain size ≈12.4 µm and F110 = 83%) exhibited the room‐temperature dielectric constant of 1708 and piezoelectric strain constant of 445 pm/V, which are higher than those of the BaTiO3 ceramics with randomly oriented grains.

Flexible amino acid-based energy harvesting for structural health monitoring of water pipes

Summary Biomolecular piezoelectric materials offer an inexpensive, non-toxic, and renewable alternative to current commercial piezoelectrics, which rely on toxic heavy elements. Currently, there is a lack of testing for real-world applications of these eco-friendly crystals. Here, we validate an amino acid-based sensor capable of real-time detection of pipe leakage, a global challenge for sustainable water access. The polycrystalline device demonstrates data-driven decision making in identifying degraded pipelines, exploiting the relationship between leak-induced vibration and piezoelectric voltage. The device has piezoelectric strain and voltage constants of 0.9 pC/N and 60 mV m/N. Peak voltage of ∼2 V is recorded in the low-dielectric film at high flow rates and large leak size. The glycine crystal sensors demonstrate much higher sensitivity than PVDF polymer patches. The sensors can operate over a range of test leak sizes, with the energy content of the worst leak state being >10 times that of a healthy pipe.

Fine scale 2-2 connectivity PZT/epoxy piezoelectric fiber composite for high frequency ultrasonic application

High frequency piezoelectric fiber composites have extensive application in fields of biomedical imaging, ultrasonic inspection, underwater acoustic imaging and so forth. In this paper, fine scale 2-2 connectivity PZT/epoxy piezoelectric fiber composites were tailored by using the dicing-filling-pressing method with poled ferroelectric ceramic (PZT) and epoxy resin, respectively. The effects of thickness and volume fraction of PZT ceramic on piezoelectric, dielectric, and acoustic properties of the composites were discussed. The results showed that the piezoelectric strain constant, relative permittivity (ε33T), thickness electromechanical coupling coefficient (kt), mechanical quality factor (Qm) and acoustic impedance of the composites exhibit an increasing trend with the increase of the volume fraction of the PZT ceramics, while the piezoelectric voltage constant (g33) showed a decreasing trend. In the low frequency range of 60−90 kHz, the planar resonance peaks can be observed in the impedance-frequency spectra, while in the high frequency range of 2−6 MHz, there only exist clear thickness resonance peaks. With increasing the PZT volume fraction, the bandwidth of the thickness vibration mode of the piezoelectric fiber composites under the same thickness increases gradually. When the PZT volume fraction keep unchanged, the thickness resonance frequency of the composites increases with decreasing the thickness as well as the bandwidth of the thickness vibration mode, which is conducive for improving the frequency response range of the ultrasonic transducer made of the proposed piezoelectric fiber composites.

Fabrication of (Bi0.5K0.5)TiO3 modified BaTiO3-Bi(Mg0.5Ti0.5)O3-BiFeO3 piezoelectric ceramics

The lead-free x(Bi0.5K0.5)TiO3-0.23BaTiO3-0.02Bi(Mg0.5Ti0.5)O3-(0.75-x)BiFeO3 piezoelectric ceramics (x = 0.05, 0.07, 0.09, and 0.11) were prepared by solid-state reaction method. The increase of (Bi0.5K0.5)TiO3 concentration revealed a decrease of dielectric maximum temperature (Tm), however, the values were higher than 420 °C. The Rietveld structure refinement for each composition showed pseudo-cubic symmetry and the rhombohedral distortion (90 - αF) was gradually decreased from 0.27° to 0.09° for x = 0.05 and 0.11, respectively. The saturation and remanent polarization were increased and a coercive field was decreased, while the critical exponent (γ) was increased from 1.407 (x = 0.07) to 1.821 (x = 0.11) revealing more relaxor-like behavior with higher (Bi0.5K0.5)TiO3 content. The remanent polarization, coercive field, and piezoelectric strain constant of 31.9 μC/cm2, 23.6 kV/cm, and 315 pm/V, respectively, obtained in the composition with x = 0.11 are significantly higher than those reported previously for other Bi-based piezoelectric ceramics with Tm>250 °C.

First-principles discovery of stable two-dimensional materials with high-level piezoelectric response

The rational design of two-dimensional (2D) piezoelectric materials has recently garnered great interest due to their increasing use in technological applications, including sensor technology, actuating devices, energy harvesting, and medical applications. Several materials possessing high piezoelectric response have been reported so far, but a high-throughput first-principles approach to estimate the piezoelectric potential of layered materials has not been performed yet. In this study, we systematically investigated the piezoelectric (e 11, d 11) and elastic (C11 and C12) properties of 128 thermodynamically stable 2D semiconductor materials by employing first-principle methods. Our high-throughput approach demonstrates that the materials containing Group-V elements produce significantly high piezoelectric strain constants, d 11 > 40 pm V−1, and 49 of the materials considered have the e 11 coefficient higher than MoS2 insomuch as BrSSb has one of the largest d 11 with a value of 373.0 pm V−1. Moreover, we established a simple empirical model in order to estimate the d 11 coefficients by utilizing the relative ionic motion in the unit cell and the polarizability of the individual elements in the compounds.

Large Piezoelectric Response and Ferroelectricity in Li and V/Nb/Ta Co-Doped w-AlN.

Enhancement of piezoelectricity in w-AlN is desired for many devices including resonators for next-generation wireless communication systems, sensors, and vibrational energy harvesters. Based on density functional theory, we show that Li and X (X = V, Nb, and Ta) co-doping in 1Li:1X ratio transforms brittle w-AlN crystal to ductile, along with broadening the compositional freedom for significantly enhanced piezoelectric response, promising them to be good alternatives to expensive Sc. Interestingly, these co-doped w-AlN also show quite large spontaneous electric polarization (e.g., about 1 C/m2 for Li0.125X0.125Al0.75N) with the possibility of ferroelectric polarization switching, opening new possibilities in wurtzite nitrides. An increase in piezoelectric stress constant (e33) with a decrease in elastic constant (C33) results in an enhancement of piezoelectric strain constant (d33), which is desired for improving the performance of bulk acoustic wave (BAW) resonators for high-frequency radio frequency (RF) signals. Also, these co-doped w-AlN are potential lead-free piezoelectric materials for energy harvesting and sensors as they improve the longitudinal electromechanical coupling constant (K332), transverse piezoelectric strain constant (d31), and figure of merit (FOM) for power generation. However, the enhancement in K332 is not as pronounced as that in d33 because co-doping increases dielectric constant. The longitudinal acoustic wave velocity (7.09 km/s) of Li0.1875Ta0.1875Al0.625N is quite comparable to that of commercially used piezoelectric LiNbO3 or LiTaO3 in special cuts (about 5-7 km/s) despite the fact that the acoustic wave velocities, important parameters for designing resonators or sensors, decrease with co-doping or Sc concentration.

Dielectric and ferroelectric properties of (Bi0.5Na0.5)0.94-δBa0.06Ti1−xNbxO3 lead-free ceramics

Lead-free ceramics (Bi0.5Na0.5)0.94-δBa0.06Ti1−xNbxO3 (x = 0, 0.01, 0.02, 0.03, 0.04, 0.05) were prepared via a solid-state sintering method. The ceramics exhibit pure perovskite structure as x ≤ 0.04, while the ceramic with x = 0.05 has a secondary phase. The rhombohedral (R)–tetragonal (T) morphotropic phase boundary exists in all the samples. The relative content of the T phase increases due to the Nb5+ doping. The ceramics show dense microstructures with mean grain sizes around 1–2 μm. The changes of dielectric constant and dielectric loss as a function of temperature for the unpoled and poled samples were compared. Two dielectric anomalies appear on the dielectric curves around the temperatures denoted as TRE and Tm. With the increase of Nb5+ amount, the values of TRE decrease and Tm increase. The Nb5+-doped ceramics exhibit better temperature stability of dielectric constant during a wide high-temperature window. The polarization hysteresis (P–E) loops change from typical ferroelectric loops for the sample with x = 0 to constricted P–E loops with increasing Nb5+ amount. The ceramic with x = 0.03 shows a maximum strain (Smax) of 0.55% and piezoelectric strain constant (d33*) of 675 pm/V.

Piezoelectricity in the proteinogenic amino acid L-leucine: A novel piezoactive bioelectret

Here, we report the growth of bioelectret crystal films of L-leucine on conductive substrates and detail the first quantitative measurements of the direct piezoelectric effect in this proteinogenic amino acid. Through extensive electromechanical characterisation, we demonstrate that L-leucine is a promising candidate material for use in non-toxic, biocompatible and biodegradable energy harvesting and sensing devices. The data presented here is among, if not the, largest set of quasi-static, longitudinal piezoelectric measurements on crystalline films of a proteinogenic amino acid to date. We substantiate these measurements using a combination of density functional theory calculations and optical microscopy. Our data provides a further example of the enormous unexploited potential of amino acids and similar biological materials in flexible energy harvesting applications. Their combination of sizeable piezoelectric strain constants and extremely low elastic and dielectric constants makes them ideal as biocompatible replacements for toxic, expensive inorganic piezoelectric materials.