High Piezoelectric Coefficient Research Articles

All-Polymer Piezoelectric Elastomer with High Stretchability, Low Hysteresis, Self-Adhesion, and UV-Blocking as Flexible Sensor.

All-polymer piezoelectric elastomers that integrate self-powered, soft, and elastic performance are attractive in the fields of flexible wearable electronics and human-machine interfaces. However, a lack of adhesion and UV-blocking performances greatly hinders the potential applications of elastomers in these emerging fields. Here, a high-performance piezoelectric elastomer with piezoelectricity, mechanical robustness, self-adhesion, and UV-resistance was developed by using poly(vinylidene fluoride) (PVDF), acrylonitrile (AN), acrylamide (AAm), and oxidized tannic acid (OTA) (named PPO). In this design, the dipole-dipole interactions between the PVDF and PAN chains promoted the content of β-PVDF, endowing high piezoelectric coefficient (d33, 58 pC/N). Besides, high stretchability (∼500%), supercompressibility (∼98%), low Young's modulus (∼0.02 MPa), and remarkable elasticity (∼13.8% hysteresis ratio) were achieved simultaneously for the elastomers. Inspired by the mussel adhesion chemistry, the OTA containing abundant catechol and quinone groups provided high adhesion (93.26 kPa to wood) and an exceptional UV-blocking property (∼99.9%). In addition, the elastomers can produce a reliable electric signal output (Vocmax = 237 mV) and show a fast response (24 ms) when subjected to external force. Furthermore, the elastomer can be easily assembled as a wearable sensor for human physiological (body pulse and speech identification) monitoring and communication.

Phase Structures, Electromechanical Responses, and Electrocaloric Effects in K0.5Na0.5NbO3 Epitaxial Film Controlled by Non-Isometric Misfit Strain

Environmentally friendly lead-free K1-xNaxNbO3 (KNN) ceramics possess electromechanical properties comparable to lead-based ferroelectric materials but cannot meet the needs of device miniaturization, and the corresponding thin films lack theoretical and experimental studies. To this end, we developed the nonlinear phenomenological theory for ferroelectric materials to study the effects of non-equiaxed misfit strain on the phase structure, electromechanical properties, and electrical response of K0.5Na0.5NbO3 epitaxial films. We constructed in-plane misfit strain (u1−u2) phase diagrams. The results show that K0.5Na0.5NbO3 epitaxial film under non-equiaxed in-plane strain can exhibit abundant phase structures, including orthorhombic a1c, a2c, and a1a2 phases, tetragonal a1, a2, and c phases, and monoclinic r12 phases. Moreover, in the vicinity of a2c−r12, a1c−c, and a1a2−a2 phase boundaries, K0.5Na0.5NbO3 epitaxial films exhibit excellent dielectric constant ε11, while at a2c−r12 and a1c−c phase boundaries, a significant piezoelectric coefficient d15 is observed. It was also found that high permittivity ε33 and piezoelectric coefficients d33 exist near the a2c−a2, a1a2−r12, and a1c−a1 phase boundaries due to the existence of polymorphic phase boundary (PPB) in the KNN system, which makes it easy to polarize near the phase boundaries, and the polarizability changes suddenly, leading to electromechanical enhancement. In addition, the results show that the K0.5Na0.5NbO3 thin films possess a large electrocaloric response at the phase boundary at the a1a2−r12 and a1c−a1 phase boundaries. The maximum adiabatic temperature change ΔT is about 3.62 K when the electric field change is 30 MV/m at room temperature, which is significantly enhanced compared with equiaxed strain. This study provides theoretical guidance for obtaining K1−xNaxNbO3 epitaxial thin films with excellent properties.

High-Temperature Electromechanical Properties Single Crystalline Lithium Niobate-Lithium Tantalate Solid Solutions at Different Oxygen Partial Pressures

LiNbO3 (LN) is one of the most investigated electro-acoustic and electro-optical materials. Its high piezoelectric coefficients are a favorable condition for its use beyond optical applications, which includes, for example, high-temperature actuators. Compared for example to crystals of the langasite family, LN shows significantly higher piezoelectric coefficients but limited thermal stability. The latter is caused by evaporation of Li2O and related changes of e.g. electrical conductivity. As a consequence, long-term applications of LN are limited to temperatures of a few hundred degrees Celsius. A related material that offers improved thermal stability is LiNbO3 (LT). However, the Curie temperature is only about 600 °C. Furthermore, the piezoelectric coefficients are lower than for LN. The miscibility of LN and LT over the entire compositional range should allow, however, to tailor the crystal properties and, for example, to take advantage of the high piezoelectric coefficients of LT and the better thermal stability of LT. Therefore, the subject of this study are lithium niobate-lithium tantalate (LiNb1-xTaxO3, LNT) solid solutions with respect to their electroacoustic properties at temperatures between 400 and 900 °C. The objectives include the determination, understanding and correlation of defect structures, electronic and atomic transport and acoustic losses in LNT over a wide temperature range.The electromechanical properties of LNT crystals are determined as function of temperature and oxygen partial pressure (pO2) and compared with those of the congruent edge compounds LN and LT. Characterization methods include impedance spectroscopy, application of 6Li as tracer in combination with secondary ion mass spectrometry, resonant piezoelectric spectroscopy, noncontacting resonant ringdown spectroscopy and laser vibrometry. The latter reflects displacements of the sample surface even in the order of nanometers which enables the identification of the resonant modes.LNT crystals with different Nb-Ta compositions prepared by Czochralski growth and a µ-pulling down process are used to determine the overall electrical conductivity by electrical impedance spectroscopy. Further, Z- and Y-cut plates are applied as bulk acoustic wave resonators to measure the acoustic loss. When determined in air, the temperature-dependent electrical conductivity of LNT below about 600 °C is virtually independent of composition. In particular, for each sample a single activation energy is found from 400 to 600 °C which is the same for all samples within the error margins. Furthermore, the diffusive ion transport studied directly using 6Li tracers results in good agreement with the electrical conductivity when the diffusion coefficients are converted correspondingly using the Nernst-Einstein relation. Consequently lithium-ion migration can explain the overall electrical conductivity. Above about 600 °C the behavior depends on composition. At high Nb contents, a continuous increase of the slope of the electrical conductivity in an Arrhenius representation with temperature is observed, which is attributed to thermal instability.The pO2 dependent electrical conductivity shows constant values at high pO2. At sufficiently low pO2, a slope of -1/4 in a double logarithmic representation is found (see attached figure). This slope indicates electronic conduction which is caused by compensation of NbLi antisite defects. The behavior is already reported for LN by Smyth et al. (Ferroelectrics 50 (1983) 93). As the slope is independent of the composition x, it can be concluded that the same defect formation occurs in LNT. Important with respect to thermal stability is that, at a given temperature, the increase in conductivity for Ta-rich compositions starts at lower pO2 than for Nb-rich compositions.The acoustic loss is determined in a wide temperature range by the methods mentioned above. It shows some impact of the metal electrodes at low temperatures. In air and at temperatures above about 400 °C the acoustic loss is governed by the piezoelectric/carrier relaxation. It is caused by the motion of charge carriers in an oscillating piezoelectric field and, therefore, related to electrical conductivity. The finding is confirmed by modelling with independent materials data including electrical conductivity. Low pO2 result in additional loss contributions.In summary, the study leads to an understanding of the acoustic losses of LNT at high temperatures, which provides opportunities to reduce them. Furthermore, it becomes clear that Ta-rich compositions exhibit improved thermal stability. Figure 1

Fine-grained high-performance Ba0.85Ca0.15 Zr0.1Ti0.9O3 piezoceramics obtained by current-controlled flash sintering of nanopowders

Due to environmental concerns, extensive research has been carried out to develop high-performance lead-free piezoceramics capable of replacing commercial lead-based materials. The lead-free (Ba0.7Ca0.3)TiO3 −Ba(Zr0.2Ti0.8)O3 system has emerged as a candidate for room temperature transducer applications because a high piezoelectric charge coefficient is achieved in this system for compositions at the morphotropic phase boundary. However, conventional ceramic processing of these eco-friendly piezoceramics demands high energy consumption because long-lasting, high-temperature heat treatments are needed, which often lead to microstructural degradation that compromises the material reliability. Field-assisted flash sintering has started to be explored since the application of an adequate electric field was shown to significantly reduce the sintering time and temperature, thereby controlling grain growth. In this work, Ba0.85Ca0.15Zr0.1Ti0.9O3 ceramics are obtained by current-controlled flash sintering of mechanosynthesized nanopowders. Exhaustive control of the sintering parameters allows tailoring of the microstructure, which allows dense fine-grained flash-sintered ceramics exhibiting a high electric field-induced strain response to be obtained.

Electrostrictive and piezoelectrical properties of chitosan-poly(3-hydroxybutyrate) blend films

Herein, we report the high apparent piezoelectric coefficient for chitosan-poly(3-hydroxybutyrate) (CS-PHB) blend films. The structure of chitosan-poly(3-hydroxybutyrate) (CS-PHB) blend films, exploiting characteristics such as dielectric, polarization, apparent piezoelectric properties, and their dependencies on the composition, were investigated. Based on the results of XRD, SEM, FTIR, PFM, and dielectric spectroscopy measurements, the structure of CS-PHB blend films has been proposed, which consists of spheric-like inclusion formed by precipitating isotactic-PHB interface layer, which consists of syndiotactic-PHB hydrogen bonding with CS, and CS matrix. The synergistic effects of piezoelectricity and electrostriction help explain the high value of the apparent piezoelectric coefficient (d33) obtained in the blend film with 13 wt% of PHB (d33 ≈ 200 pC/N). The investigated CS-PHB blend films are a good candidate for tissue engineering applications.

Structure and Relaxor Behavior of (0.5 − x)BiFeO3-0.5PbFe0.5Nb0.5O3-xPbTiO3 Ternary Ceramics

Ceramics of the quasi-binary concentration section (0.1 ≤ x ≤ 0.2, Δx = 0.025) of the ternary solid solution system (0.5 − x)BiFeO3-0.5PbFe0.5Nb0.5O3-xPbTiO3 were prepared by the conventional solid-phase reaction method. An X-ray study at different temperatures revealed that (0.5 − x)BF-0.5PFN-xPT ceramics have a cluster morphology. Clusters have different modulation, crystal lattice symmetry, and chemical composition. The presence of a cluster structure in a solid solution with heterovalent substitution, consisting of regions rich in Ti+4, Nb+5, or Fe3+, has led to the appearance of Maxwell–Wagner polarization in the studied ceramics. The study of the dielectric characteristics revealed the relaxor-like behavior of the studied ceramics. The grain morphology, dielectric, pyroelectric, and piezoelectric properties of the selected solid solutions were investigated. The highest piezoelectric coefficient, d33 = 280 pC/N, was obtained in the 0.3BiFeO3-0.5PbFe0.5Nb0.5O3-0.2PbTiO3 ceramics. Study of the dielectric characteristics of all samples revealed relaxor ferroelectric behavior and a region of diffuse phase transition from the paraelectric to ferroelectric phase in the temperature range of 140–170 °C.

Mn-doped 0.15Pb(Yb1/2Nb1/2)O3–0.48Pb(Mg1/3Nb2/3)O3–0.37PbTiO3 piezoelectric ceramics for high performance high-power transducers

For high-power transducer applications, the piezoelectric materials should fulfill specific requirements of a high mechanical quality factor (Qm), a high piezoelectric strain coefficient (dij), and a high Curie phase transition temperature (Tc). In this study, we present an investigation of the structural, piezoelectric, and high-power characteristics of Mn-doped 0.15Pb(Yb1/2Nb1/2)O3–0.48Pb(Mg1/3Nb2/3)O3–0.37PbTiO3 (0.15PYN–0.48PMN–0.37PT) ceramics. The introduction of Mn dopants led to an increase in the tetragonal phase fraction within the 0.15PYN–0.48PMN–0.37 PT ceramics and the formation of oxygen vacancies, consequently significantly enhancing Qm due to their synergistic effect. Despite the hardening effect, the high value of the piezoelectric coefficient (d33) was maintained due to the increase in grain size. Particularly, the specimen doped with 3 mol% of Mn exhibited excellent piezoelectric properties of d33 = 345 pC/N, Qm = 1159, and Tc = 207°C. This specimen displayed a high vibration velocity of 0.6 m/s under the condition of equilibrium ΔT < 20°C (temperature rise from initial temperature), thereby confirming its immense potential for high-power transducer applications.

Blue light emitting piezoelectric few-layered borophene nanosheets for flexible nanogenerators

Piezoelectric response from two-dimensional layered materials with semiconducting properties is important for developing nanogenerators, piezotronics, and piezophototronics devices. However, experimental observation of piezoelectricity and semiconductor properties in monoatomic borophene has been a key challenge for the fabrication of nanogenerator devices. Here, we discover the non-centrosymmetric blue light emitting piezoelectric properties of few layered monoatomic borophene nanosheets. We develop the flexible piezoelectric nanogenerator using few layered borophene nanosheets in polydimethylsiloxane polymer, producing an output voltage of 8 V without electrical poling. The material exhibits a high piezoelectric charge coefficient (d33) of 86 pm V−1 and shows band gap opening with a high band gap of 2.32 eV. Surprisingly, the borophene nanosheets exhibit blue light emission under UV light illumination. Under UV light illumination, the device dramatically improves output performance. We find that the material exhibits a high dielectric constant of about 125 at low frequency.

Excellent strain properties in (K,Na)NbO3-based piezoceramics induced by lamination composite strategy

To reconcile the contradiction between piezoelectric property and its temperature stability, the preparation of composite piezoceramics using multiple components has become an emerging direction. Herein, (K,Na)NbO3-based piezoceramics are adopted to prepare high-performance laminated composite ceramics inspired by the lamination composite strategy, and sintered in the reducing atmosphere to meet the development of multilayer piezoelectric actuators with base metal internal electrodes. By adjusting the composition ratio, a high inverse piezoelectric coefficient d33* of 1065 pm/V (@ 2 kV/mm) is obtained in the two-component composite ceramics, which fluctuated less than ± 6% in the range of 25–160 °C. In the three-component composite ceramics, a higher d33* value of 1326 pm/V (@ 2 kV/mm) is achieved and maintained > 90% until 150 °C. The electric-field-induced strain performances of laminated composite ceramics significantly exceed those of their basic components, which is related to the piezoresponse gain provided by the internal interfaces. The excellent temperature stabilities come from the more diffused phase transition temperature range formed by the complementation of multiple components. The combination of ultrahigh strain performance, high temperature stability, and good fatigue resistance, together with sintering in the reducing atmosphere, constitutes an important step to promote the application of (K,Na)NbO3-based multilayer piezoelectric actuators.

Lead-free Bi2CuO4 interspersed into PDMS matrix-based bifunctional piezoelectric nanogenerator for vibrational energy harvesting and visible light photodetection applications

Lead-free materials with superior piezoelectric properties are gaining much interest due to their high performance and increased long-term sustainability. In this context, bismuth-based ternary oxides exhibit perovskite crystal structures with high piezoelectric coefficients and mechanical damping. Thus, in this work, we report a Bi2CuO4: Polydimethylsiloxane (BCO: PDMS) composite -based photoinduced-piezoelectric nanogenerator for harvesting weak mechanical vibrations which are abundant in the atmosphere. Notably, the BCO nanoparticles exhibit a highly crystalline tetragonal structure with 2D-nanoflake-like morphology providing a high surface area for the PENG applications. Further, the optical studies of BCO illustrate an enhanced absorption in the visible region with a bandgap of 2.5 eV. BCO: PDMS-based PENG displays a maximum open circuit voltage of 50 V and short circuit current of 300 nA upon application of 0.15 kgf vertical compressive force without any electrical poling. The PENG device exhibits an 18 % increment in output voltage upon illumination of visible light of 5 mW/cm2 intensity with superior photodetection properties. The obtained response can be attributed to the synergistic effect, i.e., the generation of exciton pairs upon illumination and separation of charge carriers due to the inbuilt piezoelectric field. Moreover, the PENG exhibits a distinct and accurate response for feeble and subtle frequencies in the range of 3–22 Hz such as atmospheric noise, and gravity hum noise. thus, proving the superior sensitivity. The fabricated PENG device displayed a stable response for 30 min of continuous vibration displaying superior cyclic stability. This work demonstrates a combination of perovskite crystalline material and PDMS leading to the development of high-performance piezoelectric nanogenerators with future scope in frequency detection systems for security and safety applications.

Stretchable polymer composites with ultrahigh piezoelectric performance.

Flexible piezoelectric materials capable of withstanding large deformation play key roles in flexible electronics. Ferroelectric ceramics with a high piezoelectric coefficient are inherently brittle, whereas polar polymers exhibit a low piezoelectric coefficient. Here we report a highly stretchable/compressible piezoelectric composite composed of ferroelectric ceramic skeleton, elastomer matrix and relaxor ferroelectric-based hybrid at the ceramic/matrix interface as dielectric transition layers, exhibiting a giant piezoelectric coefficient of 250 picometers per volt, high electromechanical coupling factor keff of 65%, ultralow acoustic impedance of 3MRyl and high cyclic stability under 50% compression strain. The superior flexibility and piezoelectric properties are attributed to the electric polarization and mechanical load transfer paths formed by the ceramic skeleton, and dielectric mismatch mitigation between ceramic fillers and elastomer matrix by the dielectric transition layer. The synergistic fusion of ultrahigh piezoelectric properties and superior flexibility in these polymer composites is expected to drive emerging applications in flexible smart electronics.

Oriented Plate-like KNbO3 Polycrystals: Topochemical Mesocrystal Conversion and Piezoelectric and Photocatalytic Responses.

KNbO3 (KN) with a perovskite structure is an outstanding representative of lead-free piezoelectric materials, and its mesocrystals have broad application prospects in the fields of catalysis, energy storage, and conversion. However, the formation conditions of KN mesocrystals reported so far are difficult owing to their high aspect ratio and excellent preferred orientation. In this study, the solvothermal process was used successfully to prepare the flake-like potassium salt of Lindquist hexaniobate (K8Nb6O19·10H2O). Subsequently, the precursor niobate was calcined to prepare two-dimensional (2D) plate-like KN mesocrystals. The formation mechanism of the plate-like KN mesocrystals is further revealed from a paired topochemical mesocrystal conversion of K8Nb6O19·10H2O niobate. Finally, the microscopic piezoelectric and photocatalytic responses of the obtained plate-like KN mesocrystals were investigated. The high piezoelectric coefficient of plate-like KN mesocrystals implies that excellent charge separation promotes the photocatalytic performance of rhodamine B (RhB). This study provides a strategy for the efficient application of 2D oriented materials in the field of piezoelectricity and photocatalysis.

BiFeO3 Nanoparticles: The "Holy-Grail" of Piezo-Photocatalysts?

Recently, piezoelectric-based catalysis has been demonstrated to be an efficient means and promising alternative to sunlight-driven photocatalysis, where mechanical vibrations trigger redox reactions. Here, 60nm-size BiFeO3 nanoparticles are shown to be very effective for piezo-degrading Rhodamine B (RhB) model dye with record degradation rate reaching 13810Lmol-1 min-1 , and even 41 750Lmol-1 min-1 (i.e., 100% RhB degradation within 5min) when piezocatalysis is synergistically combined with sunlight photocatalysis. These BiFeO3 piezocatalytic nanoparticles are also demonstrated to be versatile toward several dyes and pharmaceutical pollutants, with over 80% piezo-decomposition within 120min. The maintained high piezoelectric coefficient combined with low dielectric constant, high-elastic modulus, and the nanosized shape make these BiFeO3 nanoparticles extremely efficient piezocatalysts. To avoid subsequent secondary pollution and enable their reusability, the BiFeO3 nanoparticles are further embedded in a polymer P(VDF-TrFE) matrix. The as-designed flexible, chemically stable, and recyclable nanocomposites still keep remarkable piezocatalytic and piezo-photocatalytic performances (i.e., 92% and 100% RhB degradation, respectively, within 20min). This work opens a new research avenue for BiFeO3 that is the model multiferroic and offers a new platform for water cleaning, as well as other applications such as water splitting, CO2 reduction, or surface purification.

Effect of bicontinuous minimal surface meso-scale geometry on piezoelectric performances of piezoelectric composites

This paper examines the effective piezoelectric properties of ceramic-based composite materials that contain bicontinuous minimal surface structures. Three structures are introduced bicontinuous Schwarz P, bicontinuous Gyroid, and bicontinuous I-WP and the material model is subjected to both compressive and tensile stresses. Using the finite element method, the relationship between the average piezoelectric coefficient and the volume fraction of piezoelectric ceramics is analyzed for different structures. The study reveals that the bicontinuous Gyroid structure exhibits the highest average piezoelectric coefficient of 501 pc/N under a compressive stress of 0.5 Gpa and a piezoelectric ceramic volume fraction of 50%. Additionally, the study compares the three bicontinuous minimal surface structures with 3–3 model piezoelectric composite materials (interconnected random distribution) to explore the piezoelectric ceramic transfer path and the impact of arrangement and combination on piezoelectric properties. The results show that bicontinuous minimal surface piezoelectric composite materials display superior piezoelectric properties, as demonstrated by their high piezoelectric charge coefficient, piezoelectric voltage coefficient, and energy harvesting figure of merit. Overall, this paper provides valuable insights into how the structure of piezoelectric ceramics can be altered to enhance the performance of piezoelectric composite materials.

Machine-learning of piezoelectric coefficients for wurtzite crystals

ABSTRACT A handful of piezoelectrics cover all of today’s technologies, so there is a need to expand the range of accessible piezoelectric properties to enable future fundamental and technological advances. Focusing on Space Group 186, we have computed the piezoelectric properties of 47 materials, and deployed machine-learning models to reveal the quantities that control them. We have found reasonable linear models for the case of wurtzites, from a dataset of only 19 entries. Some of these models are based on easily retrievable features, while others involve features requiring additional computations. In the case of non-wurtzite materials, the statistical learning has not found any meaningful correlations, since the diversity of structures and compositions in a set of 26 non-wurtzite entries obliterates the influence of features on piezoelectric coefficients. The linear models presented for the wurtzite coefficients can potentially be used to inform future searches for wurtzite-structured alloys with higher piezoelectric coefficients.

Hybrid Piezo-Capacitive Multimodal Sensors Based on Polyurethane–Poly(vinylidene fluoride) Nanofibers for Wearable E-Textiles

Wearable textiles with integrated multimodal sensors have numerous uses in the healthcare, entertainment, fitness, and fashion industries. However, the majority of reported sensors use different measurement methods to measure different stimuli, i.e., strain, pressure, and temperature. Further, they lack repeatability and stretchability for multimodal sensing. We have solved these issues by fabricating hybrid piezoelectric-capacitive sensors based on the PVDF–PU blend. Though PVDF, being a piezoelectric polymer, can be used as a dielectric layer in a capacitive sensor, it shows a poor piezoelectric coefficient and is mechanically unstable to cyclic deformations. To overcome this problem, we have used a specific blend of PU with PVDF, which has both high stretchability and piezoelectric coefficient. PVDF79PU21 (with 21% PU) nanofiber capacitive sensors showed a multimodal response with an excellent sensitivity of 0.3 kPa–1 for up to 8 kPa pressure stimuli, a good gauge factor ranging between 0.5 and 0.75 for 0–40% cyclic strain, and high sensitivities of 0.8 and 2% °C–1 for 30–60 and 60–100 °C, respectively. They could be used for measuring the human body temperature in the range of 37–40 °C with a sensitivity of 0.9% °C–1. The prototypes of PVDF79PU21 nanofiber-based capacitive sensors were attached to different body parts to measure extension and flexion movements with high sensitivity, which showed its great potential as a wearable sensor.

Textured BiScO3-PbTiO3 piezoelectric ceramics with both high electromechanical coupling factor and high curie temperature

High-temperature piezoelectric devices require piezoelectric ceramics with high Curie temperatures and high-temperature stability of piezoelectric properties to avoid the depolarization of piezoelectric ceramics during application. However, piezoelectric materials with high Curie temperatures usually have restrained piezoelectric properties. Crystallographic orientation via texture engineering is a practicable way to improve piezoelectric performance. Here, we propose a sintering-aid-assisted template grain growth strategy to texture BiScO3-PbTiO3 ceramics to overcome the low orientation issue that challenges the texturing of BS-PT for decades. By judiciously selecting B2O3-CuO as sintering aids, we fabricated highly ⟨001⟩-textured 0.43BS-0.57PT ceramics with Logtering factors &amp;gt;99.0% that possess high piezoelectric coefficients d33 of 474–612 pC/N while maintaining relatively high Curie temperatures of 370–402 °C. Importantly, this work addresses a long-standing issue presented in BS-PT ceramics, i.e., the low electromechanical coupling property of BS-PT ceramics (k33 &amp;lt; 0.70) by improving the electromechanical coupling factor k33 to 81.2%. The newly designed textured BS-PT ceramics are thought to be promising candidates for the design of high-temperature piezoelectric transducers and actuators.

Piezoelectric response of InN nanostructures grown on c-Al2O3 and Si substrates: Role of oxygen incorporation in improved piezoresponse

Materials with high piezoelectric coefficients are crucial in developing high piezopotential nanogenerators. The present study reports the effect of oxygen incorporation in improving the piezoelectric coefficient of InN nanostructures. InN nanostructures are grown on sapphire and Si substrates using the chemical vapor deposition technique. The nanostructures grown on Si substrate have a marginally higher carrier density (∼ 2.6 × 1018 cm−3) compared to that (∼ 1.8 × 1018 cm−3) for nanostructures grown on a sapphire substrate. The piezoresponse of nanostructures is studied using piezoresponse force microscopy (PFM). InN nanostructures grown on Si substrates showed one-order higher piezoresponse than nanostructures grown on a sapphire substrate. The piezoelectric coefficients (d33) are estimated to be 12 and 28 pm/V for the nanostructures grown on sapphire and Si substrates, respectively. The high piezoresponse of nanostructures grown on Si substrate is attributed to the structural instability and chemical heterogeneity induced by O defects.

Flexoelectricity and piezoelectric effects in poly (vinyl alcohol)-SrTiO3 nanocomposites

This work investigates the structural, dielectric, mechanical, and apparent piezoelectric properties of PVA-SrTiO3 nanocomposite films by varying the concentration of SrTiO3 nanoparticles. It was shown that the piezoelectric coefficient d33, dielectric constant, elastic modulus, and hardness strongly depend upon nanoparticle concentration; the strong molecular interaction between constituents leads to the formation of an interface layer between PVA matrix and SrTiO3. We propose that the apparent piezoelectric coefficient relates to the converse flexoelectric effect and Maxwell stress induced by an electric field. The proper interface layer formation strongly depends upon nanoparticle concentration; when the concentration increases, their agglomeration drives the destruction of the interface such that the properties of the nanocomposites are diminished. By fine-tuning the interface layer of PVA nanocomposite with nanoparticles functionalizing by polyvinylpyrrolidone, the films exhibit an unexpectedly high apparent piezoelectric coefficient (d33=35 pC/N); this value is higher than neat SrTiO3 crystals and polymer composites with flexoelectric properties.

Structural mechanisms of large piezoelectric responses in BiFeO3-PbTiO3 based solid-solution ceramics

Achieving large piezoelectric response and high Curie temperature, simultaneously, are of great demand but have been rarely achieved in BiFeO3-PbTiO3 (BF-PT) based morphotropic phase boundary (MPB) systems. In this work, in-situ synchrotron x-ray diffraction and transmission electron microscopy were carried out in BF-PT-0.19Ba(Zr,Ti)O3 high-temperature piezoceramic, a recently reported MPB composition with high piezoelectric coefficient, to elucidate the underlying structural mechanism. A field induced irreversible transition from tetragonal (T) P4mm phase to rhombohedral (R) R3c phase is identified although R and T phases are still coexisted after poling. This induces the significantly enhanced irreversible domain switching of both R and T phases and the reversible domain switching of R phase but only a slightly enhanced reversible switching of T phase of as compared with other BF-PT-x Ba(Zr,Ti)O3 MPB compositions, leading to the significant increase of lattice strain up to ∼0.15% but only a slightly increase of strain from extrinsic domain switching due to the strong coupling between lattice strain and domain switching in both R and T phases, although the strain contribution seems to be composition independent after the field induced irreversible phase transition. The present study demonstrates a new performance enhancement mechanism to design the high-performance BF-PT based high-temperature piezoelectric ceramics in terms of the different roles of R and T phases within MPB.