Longitudinal Piezoelectric Coefficient Research Articles

Strong Piezoelectricity and Improved Rectifier Properties in Mono‐ and Multilayered CuInP2S6

AbstractMost atomically thin piezoelectrics suffer from weak piezoelectric response or current rectification along the thickness direction, which largely hinders their applications in a vertical crossbar architecture. Therefore, exploring new types of ultrathin materials with strong longitudinal piezoelectric coefficient and rectification is highly desired. In this study, the monolayer of van der Waals CuInP2S6 (CIPS) is successfully exfoliated and its strong piezoelectricity in the out‐of‐plane direction with an effective coefficient d33eff of ≈5.12 pm V−1, which is one or two orders of magnitude higher than that of most existing monolayer materials with intrinsic d33, is confirmed. A prototype vertical device is further constructed and the current rectification is achieved through the flexoelectricity induced by the scanning tip force. The switching between low and high rectification states can be readily controlled by tuning the mechanical loads. These findings manifest that CIPS possesses promising application in vertical nanoscale piezoelectric devices and provides a novel strategy for achieving a good current rectification in ultrathin piezoelectrics.

Effect of an electric field on ferroelectric and piezoelectric properties of brownmillerite Ca2Al2O5

Brownmillerites ${A}_{2}{B}_{2}{\mathrm{O}}_{5}$ are oxides possessing a crystallographic structure that is parent from the perovskite structure ${AB\text{O}}_{3}$ with an ordered sublattice of oxygen vacancies, forming a network of one-dimensional chiral chains of oxygen tetrahedra carrying electric dipoles. The distribution of left-and right-handed chains enables the formation of different, polar or nonpolar, crystallographic phases with close internal energies. We have performed first-principles calculations on the nonmagnetic ${\mathrm{Ca}}_{2}{\mathrm{Al}}_{2}{\mathrm{O}}_{5}$ oxide, chosen as a case study, in order to investigate the effect of an external electric field, applied in the direction parallel to the chains, on the stability of four different crystallographic phases. We found that reversing the direction of the electric polarization in the $Ima2$ phase necessitates going through different intermediate phases. However, we also showed that, even if the application of the electric field allows to change the relative stability of each phase, it cannot be sufficient to change one-chain handedness at low temperature, owing to the high barrier energies, of the order of $\ensuremath{\sim}$1 eV per chain of two tetrahedra, which has to be overpassed. Switching between different phases would thus require applying an electric field at high temperature or with the application of additional stress. Finally, we demonstrated that polar phases, such as $Ima2$ or $Pmc{2}_{1}$, display negative longitudinal piezoelectric coefficients due to the lattice response to the applied electric field.

Novel manufacturing method for highly flexible poly(lactic acid) foams and ferroelectrets

Poly (lactic acid) (PLA) foams have demonstrated a high variety of functional characteristics, still, the rigidity of this cellular material remains a major limiting factor when it comes to implementation options. In this contribution, PLA foams with outstanding flexibility were created for the first time by a new approach of uniaxial stretching and immediate relaxation following supercritical CO2-assisted extrusion foaming. Instead of improving the resilience of the PLA raw material, structural elasticity of the foam was achieved via altering the deformation mechanism from cell wall collapse or rupture towards reversible and extensive flexural strain. In addition, PLA foams with excellent piezoelectric properties were also achieved via high-voltage corona poling, giving additional function to the lens-like anisotropic foam cells. This foaming technology creates the opportunity to produce PLA piezoelectrets in a way entirely different from the state-of-the-art methods. Correlation between the tensile as well as compression elongations and moduli, cell morphology and longitudinal piezoelectric coefficients (d33) of electretized foam samples were studied. Unprecedented reversible tensile elongations of up to 16% and total elongations of up to 35% were reached, as well as considerable d33 values in the range of 50–320 pC/N were obtained for PLA ferroelectrets.

Large piezoelectric anisotropy and high hydrostatic piezoelectric activity due to an appreciable orientation effect and porosity in novel 2–2–0 composites

The polarization orientation effect and porosity effect on the piezoelectric properties and related parameters are studied in 2–2-type composites based on domain-engineered relaxor-ferroelectric [011]-poled single crystals. The parameters, which are of great interest, are an anisotropy of the piezoelectric coefficients [Formula: see text], an anisotropy of the energy-harvesting figures of merit [Formula: see text] and the hydrostatic piezoelectric coefficient [Formula: see text]. An orientation of the main crystallographic axes in each polydomain single-crystal layer is described by angles [Formula: see text] and [Formula: see text]. Diagrams built for the first time show the ([Formula: see text]) regions, where a large anisotropy of [Formula: see text] (or [Formula: see text]) is achieved, and where inequality [Formula: see text] 1000 pC/N holds. A large local max [Formula: see text] = 1930 pC/N is achieved in a 2–2–0 PZN–0.065PT-based composite at the longitudinal piezoelectric coefficient [Formula: see text] = 2290 pC/N and figure of merit [Formula: see text] = 1.02[Formula: see text]10[Formula: see text] Pa[Formula: see text]. The aforementioned large parameters are to be of value in piezoelectric sensing, energy harvesting and hydroacoustics.

Low-temperature processing of screen-printed piezoelectric KNbO3 with integration onto biodegradable paper substrates

The development of fully solution-processed, biodegradable piezoelectrics is a critical step in the development of green electronics towards the worldwide reduction of harmful electronic waste. However, recent printing processes for piezoelectrics are hindered by the high sintering temperatures required for conventional perovskite fabrication techniques. Thus, a process was developed to manufacture lead-free printed piezoelectric devices at low temperatures to enable integration with eco-friendly substrates and electrodes. A printable ink was developed for screen printing potassium niobate (KNbO3) piezoelectric layers in microns of thickness at a maximum processing temperature of 120 °C with high reproducibility. Characteristic parallel plate capacitor and cantilever devices were designed and manufactured to assess the quality of this ink and evaluate its physical, dielectric, and piezoelectric characteristics; including a comparison of behaviour between conventional silicon and biodegradable paper substrates. The printed layers were 10.7–11.2 μm thick, with acceptable surface roughness values in the range of 0.4–1.1 μm. The relative permittivity of the piezoelectric layer was 29.3. The poling parameters were optimised for the piezoelectric response, with an average longitudinal piezoelectric coefficient for samples printed on paper substrates measured as d33, eff, paper = 13.57 ± 2.84 pC/N; the largest measured value was 18.37 pC/N on paper substrates. This approach to printable biodegradable piezoelectrics opens the way forward for fully solution-processed green piezoelectric devices.

Dielectric and piezoelectric properties of cement-containing piezoelectric composites: Experiments and modeling

In this work, porous honeycomb lead zirconate titanate (PZT) ceramics with one dimensional ordered pore channels were fabricated by the ionotropic gelation of sodium alginate/PZT suspension with SrCl2 solution, then the piezoelectric cement/PZT paste with different mass fraction of PZT component were cast into the porous ceramics to produce cement-containing piezoelectric composites. The influences of PZT mass fraction of piezoelectric cement/PZT paste on the microscopic morphology were studied. The relative permittivity (εr) and longitudinal piezoelectric strain coefficient (d33) of piezoelectric composites were measured and predicted by experiments and modified “unit cell” model respectively, while both results displayed consistency. The composites presented typical electromechanical coupling behavior for the direct and inverse piezoelectric effect of PZT component, when the PZT mass fraction increased to 50 wt%, the cement-containing piezoelectric composites acquired the greatest thickness electromechanical coupling coefficient (Kt) value of 55.69% and acoustic impedance (Z) value of 10.00 MRayls, making it an appropriate candidate material in the structure health monitoring system.

Phase evolution and enhanced room temperature piezoelectric properties response of lead-free Ru-doped BaTiO3 ceramic

Abstract Recent years have witnessed considerable work on the development of lead-free piezoelectric ceramic materials and their structure–property correlations. The development of piezo response is a strong function of phase evolution in these materials. In this work, we report the effect of Ru doping and consequent phase evolution on the maximization of piezoelectric response of polycrystalline lead-free barium titanate, depicted as Ba(RuxTi1-x)O3 (BRT). The samples were prepared in a narrow compositional range of 0 ≤ x ≤ 0.03 using the conventional solid-state reaction method. Ru doping increases the leakage current of BaTiO3 samples attributed to increased oxygen vacancy concentration due to substitution of Ti4+ by Ru3+. Detailed structural analysis reveals that samples exhibiting coexistence of tetragonal (space group: P4mm) and orthorhombic (space group: Amm2) structured phases near room temperature reveal relatively enhanced piezoelectric properties. The BRT sample with Ru content of 2 mol% yields a maximum longitudinal piezoelectric coefficient, d33 of ∼269 pC/N, a high strain value of 0.16% with a large remnant polarization of ∼19 µC/cm2 and a coercive field of 5.8 kV/cm. We propose that the ‘4d’ orbital of Ruthenium plays a crucial role in improving the functional properties and in decreasing the ferroelectric Curie temperature. Our work provides clues into tailoring the phase evolution for designing lead-free piezoelectric materials with enhanced piezoelectric properties.

Biodegradable and Bioabsorbable Polylactic Acid Ferroelectrets with Prominent Piezoelectric Activity

AbstractFerroelectrets have promoted a variety of exciting flexible sensors, actuators, and microenergy harvesters. However, most ferroelectrets have been fabricated from non‐degradable petro‐based resins, and thus the recycling of these materials constitutes a big challenge. This article reports biodegradable and bioabsorbable ferroelectret films made from polylactic acid (PLA) resins for highly sensitive transducer applications, which can operate either in piezoelectric 33 or 31/32 mode. By modification of the microstructure and polarization, pronounced longitudinal and transverse piezoelectric activities are realized in a single material. For samples with a thickness of 400 µm and a bulk density of 350 kg m−3, the Young's moduli in thickness and plane direction are ranging from 0.1 to 10 MPa, respectively. After polarization in the thickness direction, quasi‐static piezoelectric d33, g33, d31 (d32), and g31 (g32) coefficients in the PLA films, up to 500 pC N−1, 40 Vm N−1, −44 pC N−1, and −3.6 Vm N−1, are achieved, respectively. The longitudinal piezoelectric coefficients of the PLA films are comparable to non‐degradable polymer ferroelectrets, while the transverse piezoelectric activity is superior, which may be attributed to the reduction of Young's moduli in the plane direction. The preparation procedure of the PLA ferroelectrets is compatible with large‐scale production lines and thus can greatly promote their applications in green electronics.

Stress engineering of polycrystalline aluminum nitride thin films for strain sensing with resonant piezoelectric microbridges

For an optimized performance of micro electromechanical systems (MEMS) double-clamped bridge-type resonators for mechanical strain sensing, a modified sputter process was developed which exploits the influence of varying sputter pressure during deposition on the intrinsic stress component of functional thin films. In detail, four different, polycrystalline aluminum nitride layers, synthesized with different sputter parameter sets were characterized related to their microstructure with techniques, such as X-ray diffraction, scanning electron microscopy and atomic force microscopy, respectively. Furthermore, the intrinsic thin film stress and the longitudinal piezoelectric coefficient were evaluated. The best performing layers were integrated in the fabrication process of two MEMS resonant strain sensor devices to study the stress-related impact on the resonant device performance. The initial static buckling of the sensor devices was studied by white light interferometric measurements, whereas the frequency response as a function of externally applied as well as intrinsic strain was analyzed by laser Doppler vibrometry. The behavior of the sensor devices was compared to theoretical predications and the influence of intrinsic thin film stress on the resonance frequency as a function of strain was studied. With a precise tailoring of the intrinsic film stress, a responsivity of ∼17000 is measured, representing an improvement by a factor of ∼5 compared to state-of-the-art resonant strain sensors.

Effect of electrically induced cracks on the properties of PZT thin film capacitors

We present a study of the effect of electrically induced cracks on both the ferroelectric and piezoelectric properties of Pt/PbZr0.52Ti0.48O3 (PZT)/Pt capacitors and correlations with domain structures of PZT films. Above a threshold bipolar electric field, cracks appear inside the PZT layer thickness leading to an increase in the ferroelectric polarization (+50% for the remnant polarization, from 16 to 25 μC/cm2) and the longitudinal piezoelectric coefficient d33,f (from ∼150 to ∼220 pm/V). The use of x-ray diffraction during in situ biasing provides direct evidence for a modification of the PZT crystalline structure as well as the a/c domain configuration. After cracking, the fraction of c-domains is strongly increased, thus contributing to higher polarization and larger strain in the out-of-plane direction.

Effective Complex Permittivity of Random Composite Media: PVDF/(Na<sub>1/2</sub>Bi<sub>1/2</sub>)TiO<sub>3</sub>

The present study discusses the fabrication of non-lead ceramic/polymer composites employing (Na1/2Bi1/2)TiO3 (NBT) ceramic powder as a filler and poly(vinylidene fluoride); PVDF as a polymer matrix. The NBT (volume fraction, ϕ = 1) ceramics were synthesized using the conventional mixed-oxide method followed by the high-energy ball milling method whereas (1-ϕ)PVDF/ϕ(Na1/2Bi1/2)TiO3; 0 ≤ ϕ ≤ 0.3 composites were prepared from a melt-mixing process. It was observed that the real and imaginary parts of dielectric permittivity, ac conductivity, and longitudinal piezoelectric charge coefficient increase with the increase in NBT-content. Different dielectric mixing models were presented to determine the effective complex permittivity of the composites. Five dielectric mixture equations have been chosen to test the acceptability of experimental data. It was revealed that theoretical models as given by Bruggman, Rother-Lichtenecker, and modified Rother-Lichtenecker show good agreement with the experimental results of filler-concentration dependent alteration of effective relative permittivity and loss factor of the PVDF/NBT composite. A mathematical model of first-order exponential growth has also been proposed, which fitted excellently the experimental data (r2 > 0.998).

Quantification of the Electromechanical Measurements by Piezoresponse Force Microscopy.

Piezoresponse force microscopy (PFM) is widely used for characterization and exploration of the nanoscale properties of ferroelectrics. However, quantification of the PFM signal is challenging due to the convolution of various extrinsic and intrinsic contributions. Although quantification of the PFM amplitude signal has received considerable attention, quantification of the PFM phase signal has not been addressed. A properly calibrated PFM phase signal can provide valuable information on the sign of the local piezoelectric coefficient-an important and nontrivial issue for emerging ferroelectrics. In this work, two complementary methodologies to calibrate the PFM phase signal are discussed. The first approach is based on using a standard reference sample with well-known independently measured piezoelectric coefficients, while the second approach exploitsthe electrostatic sample-cantilever interactions to determine the parasitic phase offset. Application of these methodologies to studies of the piezoelectric behavior in ferroelectric HfO2 -based thin-film capacitors reveals intriguing variations in the sign of the longitudinal piezoelectric coefficient, d33,eff . It is shown that the piezoelectric properties of the HfO2 -based capacitors are inherently sensitive to their thickness, electrodes, as well as deposition methods, and can exhibit wide variations including a d33,eff sign change within a single device.

Depolarization of ferroelectric materials measured by their piezoelectric and elastic response

Depolarization in ferroelectric materials limits their piezoelectric applications and needs careful calibration for device constructions. With BaTiO 3 and PbSc 0.5 Ta 0.5 O 3 as prototypic ferroelectrics we demonstrate how to apply Resonant Piezoelectric Spectroscopy, RPS, to measure the direct and the converse piezoelectric effects as a function of temperature to detect depolarization via the collapse of the piezoelectric effect and the anomaly of elastic moduli. Comparison of the RPS data with in-situ d 33 measurements on a BaTiO 3 ceramic shows that the temperature evolution of the longitudinal piezoelectric coefficient d 33 can be determined with high accuracy. This makes RPS a complementary and convenient method for the investigation of polar phase transitions and the thermal evolution of the piezoelectric effect. Finally, the observation of an elastic anomaly concomitant to depolarization indicates that elastic measurements are an indirect means to measure the depolarization temperature in ferroelectrics. • RPS is a versatile and complementary technique for measuring depolarization in ferroelectrics with the ability for in-situ poling. • RPS can accurately measure the thermal evolution of the longitudinal piezoelectric coefficient d 33 , which is important for many technological applications. • Elastic measurements are an indirect means to measure the depolarization temperature in ferroelectrics.

Flash Sintered Potassium Sodium Niobate: High-Performance Piezoelectric Ceramics at Low Thermal Budget Processing.

Alternative sintering technologies promise to overcome issues associated with conventional ceramic sintering such as high thermal budgets and CO2 footprint. The sintering process becomes even more relevant for alkali-based piezoelectric ceramics such as K0.5Na0.5NbO3 (KNN) typically fired above 1100 °C for several hours that induces secondary phase formation and, thereby, degrades their electrical characteristics. Here, an ability of KNN ceramics to be of high performance is successfully demonstrated, using an electric field- and current-assisted Flash sintering technique at 900 °C only. Reported for the first time, Flash sintered KNN ceramics have room-temperature remnant polarization Pr = 21 μC/cm2 and longitudinal piezoelectric coefficient d33 = 117 pC/N, slightly superior to that of conventional ones due to the reduced content of secondary phases. High-performance KNN ceramics Flash sintered at a low-thermal budget have implications for the development of innovative low carbon technologies, electroceramics stakeholders, and piezoelectric energy harvesters.

Homogenization of electrets with ellipsoidal microstructure and pathways for designing piezoelectricity in soft materials

True piezoelectricity in soft materials is rare if not virtually non-existent. This impedes applications where both large deformation and a strong electromechanical coupling are desirable e.g. soft robotics, biomedical sensors and actuators, a class of energy harvesting devices among others. The widely used soft dielectric elastomers rely on the electrostatic Maxwell stress effect for electromechanical coupling — a one-way quadratic effect that requires extremely large voltage for actuation and does not allow for the facile conversion of mechanical deformation into electricity. Prior research has shown that embedding (and stabilizing) immobile charges or dipoles in soft matter i.e. creating so-called electrets, can lead to an emergent piezoelectric effect. In this work, using a recently developed homogenization theory for soft electret materials, we derive closed-form expressions to design soft apparently piezoelectric materials with an ellipsoidal microstructure. Specifically, we determine both effective longitudinal (d33) and transverse (d31) piezoelectric coefficients of the material and study the impact of the material properties on these two coefficients. Conventional electrets exhibit a rather weak d31, which is quite disadvantageous for applications where flexure is important (e.g. energy harvesting). Either an elastic, or a dielectric contrast is essential for the emergence of piezoelectricity in electrets and, depending on the microstructural details, these two effects can either strengthen or diminish the other. Our results indicate that the microstructure and material properties which lead to an optimum d33 effect are different from the conditions underlying the optimal d31 response. The maximum d31 effect is observed in electrets where the inclusions are mechanically harder but dielectrically softer than the matrix material. Finally, we find that a significantly large d33 piezoelectric response is possible for spheroid inclusion microstructures with large aspect ratios.

Nanoscale Doping and Its Impact on the Ferroelectric and Piezoelectric Properties of Hf0.5Zr0.5O2.

Ferroelectric hafnium oxide thin films—the most promising materials in microelectronics’ non-volatile memory—exhibit both unconventional ferroelectricity and unconventional piezoelectricity. Their exact origin remains controversial, and the relationship between ferroelectric and piezoelectric properties remains unclear. We introduce a new method to investigate this issue, which consists in a local controlled modification of the ferroelectric and piezoelectric properties within a single Hf0.5Zr0.5O2 capacitor device through local doping and a further comparative nanoscopic analysis of the modified regions. By comparing the ferroelectric properties of Ga-doped Hf0.5Zr0.5O2 thin films with the results of piezoresponse force microscopy and their simulation, as well as with the results of in situ synchrotron X-ray microdiffractometry, we demonstrate that, depending on the doping concentration, ferroelectric Hf0.5Zr0.5O2 has either a negative or a positive longitudinal piezoelectric coefficient, and its maximal value is −0.3 pm/V. This is several hundreds or thousands of times less than those of classical ferroelectrics. These changes in piezoelectric properties are accompanied by either improved or decreased remnant polarization, as well as partial or complete domain switching. We conclude that various ferroelectric and piezoelectric properties, and the relationships between them, can be designed for Hf0.5Zr0.5O2 via oxygen vacancies and mechanical-strain engineering, e.g., by doping ferroelectric films.

Development and Characterization of ZnO Piezoelectric Thin Film Sensors on GH4169 Superalloy Steel Substrate by Magnetron Sputtering.

At present, piezoelectric sensors are primarily applied in health monitoring areas. They may fall off owing to the adhesive’s durability, and even damage the monitored equipment. In this paper, a piezoelectric film sensor (PFS) based on a positive piezoelectric effect (PPE) is presented and a ZnO film is deposited on a GH4169 superalloy steel (GSS) substrate using magnetron sputtering. The microstructure and micrograph of ZnO piezoelectric thin films were analyzed by an X-ray diffractometer (XRD), energy dispersive spectrometer (EDS), scanning electron microscope (SEM), and atomic force microscope (AFM). The results showed that the surface morphology was dense and uniform and had a good c-axis-preferred orientation. According to the test results of five piezoelectric sensors, the average value of the longitudinal piezoelectric coefficient was 1.36 pC/N, and the average value of the static calibration sensitivity was 19.77 mV/N. We selected the sensor whose parameters are closest to the average value for the dynamic test experiment and we drew the output voltage response curve of the piezoelectric film sensor under different loads. The measurement error was 4.03% when repeating the experiment six times. The research achievements reveal the excellent performance of the piezoelectric film sensor directly deposited on a GH4169 superalloy steel substrate. This method can reduce measurement error caused by the adhesive and reduce the risk of falling off caused by the aging of the adhesive, which provides a basis for the research of smart bolts and guarantees a better application in structural health monitoring (SHM).

Enhanced piezoelectric performance of PVDF/BiCl3/ZnO nanofiber-based piezoelectric nanogenerator

A unique bismuth chloride (BiCl3)/zinc oxide (ZnO)/poly(vinylidene fluoride) (PVDF) nanofiber-based highly flexible piezoelectric nanogenerator (PENG) is prepared via electrospinning technique. Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) are used to characterize the β-phase content and crystallinity of the PVDF based nanofibers, respectively. Then, we analyze four types nanofiber-based PENG (PVDF, PVDF/ZnO(2%), PVDF/BiCl3(2%), and PVDF/BiCl3/ZnO(2%)) and the influence factors of piezoelectric properties are addressed systematically. It is found that the longitudinal piezoelectric coefficient (d33) of PVDF/BiCl3/ZnO(2%) nanofiber-based PENG is up to 3.8 pC/N and an open-circuit voltage (VOC) of 12 V is also got. Finally, the practical applicability of the developed PENG is demonstrated by placing it on elbow and knee joint to monitor human body movement, which shows a maximum peak VOC of 3 V (for elbow) and 0.6 V (for knee) by bending and stretching between specific angles. The high-performance flexible PENG can be used as highly sensitive self-powered sensor, and it also can be used for wearable sensors for detecting some vital signals including breathing, heartbeating, which shows its possible applications in wearable electronics.

Quasi-laminate and quasi-columnate modeling of dielectric and piezoelectric properties of cubic-cell metamaterials

Dielectric and piezoelectric properties of closed-cell or open-cell metamaterials with cubic cells are predicted analytically via quasi-laminate / Q-lam and quasi-columnate / Q-col models. For dielectric properties also numerical results are given. Model predictions of relative permittivity are within the Wiener bounds. Q-lam model predictions are higher than Q-col model predictions (and even exceed the Hashin-Shtrikman upper bound), but the numerical results are in between these two predictions. Closed-cell metamaterials exhibit higher permittivity than open-cell metamaterials. The classical predictions by Rittenmyer et al. and Banno correspond to the Q-col model predictions for open-cell and closed-cell metamaterials, respectively. Model predictions for longitudinal piezoelectric charge coefficients are close to Newnham’s parallel model, i.e. relatively constant over a wide range of porosity, with a steep decrease as the porosity approaches 100 %. Brief comments are given on the transverse piezoelectric charge coefficient, the hydrostatic piezoelectric charge coefficient and the piezoelectric voltage coefficient.

Piezoelectricity in binary wurtzite semiconductors: a first-principles study

Using first-principles calculations, we investigate piezoelectricity in a wide range of binary wurtzite semiconductors. We find that piezoelectricity is intimately related to the bond character, e.g. the negative longitudinal piezoelectric effect (NLPE) tends to occur in covalent compounds. We further find a universal sign rule (negative clamped-ion term and positive internal-strain term) for piezoelectricity, and the NLPE occurs as a result of the domination of the former over the latter. Moreover, there exists an inverse linear correlation between the longitudinal and transverse piezoelectric coefficients. This work may offer a simple criterion for efficient computational screening of materials exhibiting the NLPE.