Piezoelectric Domain Research Articles

Piezo-Photocatalysis – a Promising Strategy for Energy Conversion

Piezocatalysis has gained considerable attention since it can deliver appreciable efficiencies by coupling the piezotronic and electrochemical effects. The piezopotentials generated by external stress are efficient in inducing charge carrier separation, thereby enabling energy conversion from mechanical energy (ultrasound, wind, and tidal) to chemical energy (hydrogen). However, the piezocatalytic hydrogen evolution reaction (HER) efficiencies currently remain lower than those from electrolysis or photocatalysis. An alternative approach to improve the HER performance is to activate the material using combined ultrasound and light (viz., piezo-photocatalysis). During the piezo-photocatalysis, the synergistic effect in charge carrier generation and separation from the creation of piezoelectric potential and photoactivation will lead to an enhanced HER efficiency. These phenomena indicate the synergy of the two processes, where the initial activation of the material by piezocatalysis overcomes the limitation of photocatalysis alone, thereby facilitating subsequent charge carrier generation and separation by combined piezocatalysis and photocatalysis.Our present work reveals the potential of piezo-photocatalytic in energy conversion,especially in splitting of water and seawater, using lead-free perovskites, including BaTiO3-x (BTO) [1] and Na0.5Bi0.5TiO3 (NBT) [2] nanoparticles. The BTO was purchased commercially, and further heat treated in H2 to create defects. This annealing conditions were observed to impact the extent of Ti4+ → Ti(4-x)+ reductions and subsequent defect formation, leading to structural alterations which affected the stability of piezoelectric tetragonal BTO domains. Furthermore, reduction also altered the energy band structure. An efficient H2 evolution rate of 132.4 μmol/g/h was achieved from DI water using piezo-photocatalysis. On the other hand, the NBT was synthesized hydrothermally and then its defect structures were modified by varying the NaOH concentration. This engineering facilitates the substitution of Bi3+ by Na+ in the NBT solid solution, which also enables the regulation of oxygen vacancy and modification of the band structure. Consequently, the NBT exhibited an efficient HER rate of 140 μmol/g/h from DI water through piezo-photocatalysis. More significantly, the heterojunction also causes notable seawater splitting capability, with the HER rates of 68 μmol/g/h from simulated seawater and 58 μmol/g/h from natural seawater.This approach of piezo-photocatalysis represents a new strategy for commercial H2 production, potentially using large-scale green technologies, including ultrasound vibrations deriving from wind energy and/or tidal energy (piezocatalysis) and sunlight (photocatalysis). It has the potential to provide the bases for novel systems aimed at a net zero emissions future while driving economic growth.[1] Y. Jiang, C. Y. Toe, S. S. Mofarah, C. Cazorla, S. L. Chang, Y. Yin, Q. Zhang, P. Koshy, & C. C. Sorrell, ACS Sustainable Chemistry Engineering 11(8), 3370-3389 (2023).[2] Y. Jiang, Zhou. S, S. S. Mofarah, P. Koshy, D. Wang & C. C. Sorrell, Nano Energy, 116, 108830 (2023). Figure 1

Giant Piezoelectric Coefficient of Polyvinylidene Fluoride with Rationally Engineered Ultrafine Domains Achieved by Rapid Freezing Processing.

Domains play an essential role in determining the piezoelectric properties of polymers. The conventional method for achieving ultrafine piezoelectric domain structures for polymers is multiphase polymerization, which is not the primary choice for industrial-scale applications because of its complex synthesis and weak mechanical properties. In this study, it is demonstrated for the first time that a nanoscale domain design can be achieved in a commercially available polyvinylidene fluoride (PVDF) homopolymer through a simple fabrication method involving cyclic compression and rapid freezing. The domain-engineered PVDF exhibits largely enhanced piezoelectric output with a record-breaking piezoelectric coefficient (d33) of 191.4 picocoulombs per Newton (8.9 times higher than that of PVDF without engineered domain structure) and electromechanical coupling factor (k33) of 77.1%. Moreover, nanoscale domain-induced ferroelectric and dielectric evolutions are revealed. A smaller domain is found to be beneficial for domain switching. An in-depth understanding of the interplay between the domain structure and piezoelectric properties reveals a simple, low-cost method for fabricating high-performance polymeric piezoelectric.

Quantitative piezoelectric measurements of partially released Pb(Zr, Ti)O3 structures

The effective large signal longitudinal piezoelectric coefficient (d33,f∗) of piezoelectric thin films on rigid substrates has been widely investigated. Unclamped piezoelectric thin films are predicted to have a higher d33,f∗ coefficient due to reduced constraints on piezoelectric strain, domain reorientation, and domain wall motion, but quantitative measurements of this coefficient have been limited. This study uses microfabrication techniques along with double-beam laser interferometry (DBLI) to accurately determine the longitudinal piezoelectric coefficient of Pb(Zr,Ti)O3 thin films in partially released piezomicroelectromechanical structures. A two-step backside release process was used: first, deep reactive ion etching to create backside vias and second, wet etching of the ZnO sacrificial layer to release the area beneath the Pb(Zr,Ti)O3 thin films. Post wet etching, optical profilometry showed concavely deformed diaphragms resulting from asymmetrical stress profiles through the diaphragm thickness. DBLI was then used to examine diaphragm deflection under an applied unipolar voltage ranging from 0 to 10 V. Devices with 50% and 75% of the area beneath the top electrode released exhibited large signal d33,f∗ values of 410 ± 6 and 420 ± 8 pm/V, respectively, more than three times higher than the d33,f∗ value of the clamped samples: 126 ± 13 pm/V. The reasons contributing to the large d33,f∗ include (i) the change in stress levels due to the release process, (ii) the elimination of mechanical constraints from substrate clamping, and (iii) enhanced domain reorientation. These findings confirm that substrate declamping significantly boosts the piezoelectric coefficient, bringing d33,f∗ closer to the bulk longitudinal piezoelectric coefficient (d33).

Room-temperature ferroelectric, piezoelectric and resistive switching behaviors of single-element Te nanowires

Ferroelectrics are essential in memory devices for multi-bit storage and high-density integration. Ferroelectricity mainly exists in compounds but rare in single-element materials due to their lack of spontaneous polarization in the latter. However, we report a room-temperature ferroelectricity in quasi-one-dimensional Te nanowires. Piezoelectric characteristics, ferroelectric loops and domain reversals are clearly observed. We attribute the ferroelectricity to the ion displacement created by the interlayer interaction between lone-pair electrons. Ferroelectric polarization can induce a strong field effect on the transport along the Te chain, giving rise to a self-gated ferroelectric field-effect transistor. By utilizing ferroelectric Te nanowire as channel, the device exhibits high mobility (~220 cm2·V−1·s−1), continuous-variable resistive states can be observed with long-term retention (>105 s), fast speed (<20 ns) and high-density storage (>1.92 TB/cm2). Our work provides opportunities for single-element ferroelectrics and advances practical applications such as ultrahigh-density data storage and computing-in-memory devices.

Lateral Piezoelectricity of Alzheimer's Aβ Aggregates.

Alzheimer's disease (AD) is the most frequent neurodegenerative disorder in the elderly aged over 65. The extracellular accumulation of beta-amyloid (Aβ) aggregates in the brain is considered as the major event worsening the AD symptoms, but its underlying reason has remained unclear. Here the piezoelectric characteristics of Aβ aggregates are revealed. The vector piezoresponse force microscopy (PFM) analysis results exhibit that Aβ fibrils have spiraling piezoelectric domains along the length and a lateral piezoelectric constant of 44.1 pC N-1. Also, the continuous sideband Kelvin probe force microscopy (KPFM) images display that the increment of charge-induced surface potential on a single Aβ fibril is allowed to reach above +1700mV in response to applied forces. These findings shed light on the peculiar mechano-electrical surface properties of pathological Aβ fibrils that exceed those of normal body components.

Enhanced energy-storage and magnetoelectric properties of Ba0.95La0.05Zr0.4Ti0.6O3/CoFe2O4 multilayer thin films

Multifunctional thin films and devices have gained much interest in both scientific and industrial research for futuristic multifunctional micro- and nano-device applications. Here, we report the development of a multi-layer structure based on relaxor-ferroelectric Ba0.95La0.05Zr0.4Ti0.6O3 (BLZT) and ferrimagnetic CoFe2O4 (CFO) ([BLZT/CFO]3/BLZT or BLZT/CFO) thin-films on Si substrates for enhanced energy-storage density and magnetic properties. An ultrahigh recoverable energy-storage density (Ur) of 137.6 J/cm3 together with an energy efficiency of 76.6 % are achieved for the BLZT/CFO multi-layer, owing to the enhanced breakdown-strength (EBD) of 8.0 MV/cm (BLZT single-layer has an Ur value of 84.7 J/cm3 at EBD of 5.5 MV/cm). Moreover, the saturation magnetization of CFO layers in the BLZT/CFO multi-layer significantly increases from 239.2 kA/m to 276.4 kA/m. This enhancement can be attributed to the enlarged magnetic domains in CFO layers, which follow the piezoelectric domain switching in the BLZT layers induced by applying a dc-bias voltage. These remarkable performances indicate that the BLZT/CFO multi-layer is a promising candidate for multifunctional energy storage and magnetoelectric device applications.

Enhanced piezoelectric properties and depolarization temperature in textured (Bi0.5Na0.5)TiO3-based ceramics via homoepitaxial templated grain growth

Enhanced piezoelectric response was usually achieved in (Bi0.5Na0.5)TiO3 (BNT)-based ceramics with sacrifice of depolarization temperature Td, seriously limiting their usage range in electromechanical applications. In this work, we propose to explore piezoelectric anisotropy and domain engineering in composition & microstructure-controlled textured ceramics to resolve this issue. [001]c-textured 0.94(Bi0.5Na0.5)TiO3–0.06BaTiO3 (0.94BNT-0.06BT) ceramics with Lotgering factor F001∼91% were fabricated through homoepitaxial templated grain growth (TGG) via using 0.94BNT-0.06BT microplatelet templates. The textured samples exhibited more ordered domains with facilitated domain switching behavior, being consistent with saturated high polarization achieved at lower electric fields. Increasing F001 to above 60% enables rapid enhancement of piezoelectric response. Notably, compared to non-textured counterpart, the maximally textured ceramics exhibited ∼236% enhanced piezoelectric coefficient (d33∼302 pC/N) and ∼280% enhanced piezoelectric voltage coefficient (g33∼49.8 × 10−3 Vm/N), together with slightly increased depolarization temperature (Td∼106 °C). Moreover, those values are approaching or even higher than the single-crystal values. This work not only provides important guidelines for design and synthesis of novel textured ceramics with improved comprehensive electrical properties, but also can expand application fields of BNT-based ceramics.

Efficient Cocatalyst-Free Piezo-Photocatalytic Hydrogen Evolution of Defective BaTiO3–x Nanoparticles from Seawater

Hydrogen is a promising fossil-fuel alternative fuel owing to its environmentally neutral emissions and high energy density. However, the need for purified water and external power are critical hindrances to the implementation of hydrogen production. The present work demonstrates the potential to overcome these shortcomings through piezo-photocatalysis of seawater using defective BaTiO3–x (BTO) nanoparticles. This material was made piezoelectrically active by a straightforward annealing process under different atmospheres, including O2, N2, Ar, or H2, the latter of which caused Ti4+ → Ti(4–x)+ multiple reductions and structural distortions that stabilize piezoelectric tetragonal domains. A suite of experimental techniques was employed to reveal the effects of reduction on the energy band structure. A substantial piezoelectric effect and the presence of self-polarization were confirmed by piezoresponse force microscopy, while simulation work clarified the role of vibrations on band bending deriving from the self-polarization. The hydrogen evolution through photocatalysis, piezocatalysis, and piezo-photocatalysis over the defective BaTiO3–x nanoparticles was characterized with deionized (DI) water, simulated seawater, and natural seawater. A promising HER with a rate of 132.4 μmol/g/h was achieved using DI water through piezo-photocatalysis without a cocatalyst. In contrast, a substantial HER rate of 48.7 μmol/g/h was obtained for natural seawater, despite the deleterious impact of dissolved ions. The present work offers new perspectives for large-scale green H2 production using abundant natural resources with a conventional piezoelectric material that is readily available but still affected by the ions dissolved in seawater.

First-principles calculation method for periodic system under external electromagnetic field

The influence of electromagnetic field on material characteristics remains a pivotal concern in scientific researches. Nonetheless, in the realm of computational condensed matter physics, the extension of traditional density functional theory to scenarios inclusive of external electromagentic fields poses considerable challenges. These issues largely stem from the disruption of translational symmetry by external fields inherent in periodic systems, rendering Bloch's theorem inoperative. Consequently, the using the first-principles method to calculate material properties in the presence of external fields becomes an intricate task, especially in circumstances where the external field cannot be approximated as a minor perturbation. Over the past two decades, a significant number of scholars within the field of computational condensed matter physics have dedicated their efforts to the formulation and refinement of first-principles computational method adopted in handling periodic systems subjected to finite external fields. This work attempts to systematically summarize these theoretical methods and their applications in the broad spectrum, including but not limited to ferroelectric, piezoelectric, ferromagnetic, and multiferroic domains. In the first part of this paper, we provide a succinct exposition of modern theory of polarization and delineate the process of constructing two computation methods in finite electric fields predicated by this theory in conjunction with density functional theory. The succeeding segment focuses on the integration of external magnetic fields into density functional theory and examining the accompanying computational procedures alongside the challenges they present. In the third part, we firstly review the first-principles effective Hamiltonian method, which is widely used in the study of magnetic, ferroelectric and multiferroic systems, and its adaptability to the case involving external fields. Finally, we discuss the exciting developments of constructing effective Hamiltonian models by using machine learning neural network methods , and their extensions according to the external fields.

Melt-stretched poly(vinylidene fluoride)/zinc oxide nanocomposite films with enhanced piezoelectricity by stress concentrations in piezoelectric domains for wearable electronics

Till date, fabrication of polymeric-inorganic piezoelectric nanocomposites with enhanced piezoelectricity is considered a potential solution for future high-performance flexible sensing devices. Herein, we report the preparation of poly(vinylidene fluoride)/zinc oxide (PVDF/ZnO) piezoelectric nanocomposite films via a combined approach of adding nanofillers, irradiation crosslinking and melt stretching. The melt-stretched film contains closely aligned β-phase nanofibrils with a high content (>90 % of the crystalline phase) serving as piezoelectric domains. Meanwhile, the incorporation of ZnO nanoparticles creates stress concentrations, promoting the piezoelectric response of β-nanofibrils and also the stress-induced polarization under loading. As a result, the film displays not only a superior mechanical strength (>100 MPa), but also largely enhanced piezoelectric output performance after poling, including wide response range, high sensibility to weak force and excellent working durability (>10,000 cycles). The optimal film with ZnO content of 5 wt% has a pressure sensitivity of ∼ 1.7 V/kPa under 0–1 kPa, almost twice that (∼0.8 V/kPa) of the pure PVDF without nanofillers. With the outstanding piezoelectric properties, potential applications of film as a flexible wearable sensor in monitoring human motions and subtle physiological signals are demonstrated. The results provide a new melt processing strategy that is easily scalable for developing high-performance PVDF-based piezoelectric nanocomposite films towards wearable electronics.

Enhanced piezoelectric properties and domain morphology under alternating current electric field poled in [001]-oriented PIN-PMN-PT single crystal

The piezoelectric and dielectric properties of PMN-PT single crystals were significantly enhanced by alternating current electric field poling (ACP). In this work, to investigate the mechanisms of piezoelectric performance enhancement in relaxor ferroelectric single crystals by ACP, a [001]-oriented PIN-PMN-PT single crystal with a diameter of 3 in was grown by the modified Bridgman method, and a series of single crystal samples within 100 mm of the height of the crystal boule were prepared. Compared with their direct current electric field poling (DCP) counterparts, the electrical properties of single crystal samples at different heights by ACP were regularly enhanced. The piezoelectric coefficient d33 and the dielectric constant ɛ33 of the rhombohedral samples both increased by nearly 20%. Based on the results of polarized light microscopy, the domain wall in [001]-poled ACP samples could not be observed along the [001] direction. The brightness of polarized light propagating along the [010] orientation was enhanced after ACP. The domain images of {100} in the DCP and ACP samples were observed by piezoelectric force microscopy. The results showed that the domain size of ACP samples increased. The existence of layered domains can be clearly found in the scanning electron microscopy results of the stress fracture surface of the ACP sample. According to the analysis, the improvement of the piezoelectric performance in ACP samples comes from the elimination of the 71° domain walls. This work demonstrates that certain ACPs can regulate the domain structure and steadily improve the piezoelectric properties of R-phase PIN-PMN-PT single crystals.

Van der Waals Exfoliation Processed Biopiezoelectric Submucosa Ultrathin Films.

Piezoelectric biomaterials have attracted significant attention due to the potential effect of piezoelectricity on biological tissues and their versatile applications. However, the high cost and complexity of assembling and domain aligning biomolecules at a large scale, and the disordered arrangement of piezoelectric domains as well as the lack of ferroelectricity in natural biological tissues remain a roadblock toward practical applications. Here, utilizing the weak van der Waals interaction in the layered structure of small intestinal submucosa (SIS), a van der Waals exfoliation (vdWE) process is reported to fabricate ultrathin films down to the thickness of the effective piezoelectric domain. Based on that, the piezoelectric property is revealed of SIS stemming from the collagen fibril, with piezoelectric coefficients up to 4.1 pm V-1 and in-plane polarization orientation parallel to the fibril axis. Furthermore, a biosensor based on the vdWE-processed SIS film with an in-plane electrode is demonstrated that produces open-circuit voltages of ≈250mV under the cantilever vibration condition. The vdWE method shows great potential in facilely fabricating ultrathin films of soft tissues and biosensors.

High performance high-power textured Mn/Cu-doped PIN-PMN-PT ceramics

Piezoelectric ceramics with combinatory soft and hard characteristics are highly desired for high-power applications. However, it remains grand challenge to achieve simultaneous presence of hard (e.g. high coercive field, Ec; high mechanical quality factor, Qm) and soft (e.g. high piezoelectric constant, d; high electromechanical coupling factor, k) piezoelectric properties in piezoelectric ceramics since the mechanism controlling the hard behavior (pinned domain walls) will significantly reduce the soft behavior. Here, we address this grand challenge and demonstrate <001> textured MnO2 and CuO co-doped Pb(In1/2Nb1/2)O3- Pb(Mg1/3Nb2/3)O3-PbTiO3 (PIN-PMN-PT) ceramics exhibiting ultrahigh combined soft and hard piezoelectric properties (d33 = 713 pC N−1, k31 = 0.52, Qm≈950, Ec = 9.6 kV cm−1, tan δ = 0.45%). The outstanding electromechanical properties are explained by considering composition/phase selection, crystallographic anisotropy and defect engineering. Phase-field model in conjunction with high resolution electron microscopy and diffraction techniques is utilized to delineate the contributions arising from intrinsic piezoelectric response, domain dynamics, and local structural heterogeneity. These results will have significant impact in the development of high-power transducers and actuators.

Mixed finite elements applied to acoustic wave problems in compressible viscous fluids under piezoelectric actuation

In the present contribution, we develop a mixed finite element method capable of the coupled multi-field simulation of a viscous fluid actuated by a piezoelectric resonator. Several challenges are met with in this setting, among which are the necessity of correct interface coupling, near incompressibility of the fluid, adverse geometric dimensions of flat piezoelectric transducers and different length scales of shear and pressure wave. Assuming small deformations and velocities, we present a mixed variational formulation with consistent interface coupling conditions in (mechanic) frequency domain. Both fluid and piezoelectric solid domain are discretized using Tangential-Displacement Normal-Normal-Stress elements. These elements model not only the deformation, but add an independent tensor-valued stress approximation. The method has been rigorously proven to be free from shear locking for flat prismatic or hexahedral elements. Thus, modeling of the flat geometry of piezoelectric resonators as well as resolution of the fastly decaying shear wave are facilitated. To circumvent the problem of volume locking due to the near incompressibility of the fluid, an additional independent pressure field is introduced. We present computational results indicating the capability of the method.

Energy Harvesting With Thermally Induced Vibrations in Shape Memory Alloys by a Constant Temperature Heater

This article reports a theoretical and experimental study of a novel thermal energy harvester with heat-induced vibrations in an environment with a nonzero temperature gradient. The energy harvester comprises a shape memory alloy wire from Nitinol and two elastic cantilever beams with deposited lead zirconium titanate piezoelectric layers. The shape memory alloy wire is prestrained by the free ends of the cantilever beams connected in a bow-similar structure. The environment temperature gradient is obtained from the difference in temperatures of a heater and colder air in the room. When the wire approaches the heater, it heats up and shortens, causing it to move away from the hot zone and entering into a colder zone. This causes the wire to cool and to approach the heater again. The cyclic change of the length of the shape memory alloy wire causes vibrations in the cantilever beams due to which electricity is produced by the piezoelectric layers. A dynamical model, based on the theory of Lagrange and Maxwell, combining mechanical, piezoelectric, and thermal domains is derived and used to prove the concept of the developed novel device and for theoretical investigation of the energy harvester performance. The hysteretic behavior of the shape memory alloy is involved in the model. The theoretical results have been proved experimentally.

Melt-Stretched Poly(Vinylidene Fluoride)/Zinc Oxide Nanocomposite Films with Enhanced Piezoelectricity by Stress Concentration in Active Piezoelectric Domains for Wearable Electronics

Melt-Stretched Poly(Vinylidene Fluoride)/Zinc Oxide Nanocomposite Films with Enhanced Piezoelectricity by Stress Concentration in Active Piezoelectric Domains for Wearable Electronics

Microscopic piezoelectric behavior of clamped and membrane (001) PMN-30PT thin films

Bulk single-crystal relaxor-ferroelectrics, like Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT), are widely known for their large piezoelectricity. This is attributed to polarization rotation, which is facilitated by the presence of various crystal symmetries for compositions near a morphotropic phase boundary. Relaxor-ferroelectric thin films, which are necessary for low-voltage applications, suffer a reduction in their piezoelectric response due to clamping by the passive substrate. To understand the microscopic behavior of this adverse phenomenon, we employ the AC electric field driven in-operando synchrotron x-ray diffraction on patterned device structures to investigate the piezoelectric domain behavior under an electric field for both a clamped (001) PMN-PT thin film on Si and a (001) PMN-PT membrane released from its substrate. In the clamped film, the substrate inhibits the field-induced rhombohedral (R) to tetragonal (T) phase transition resulting in a reversible R to Monoclinic (M) transition with a reduced longitudinal piezoelectric coefficient d33 &amp;lt; 100 pm/V. Releasing the film from the substrate results in recovery of the R to T transition and results in a d33 &amp;gt; 1000 pm/V. Using diffraction with spatial mapping, we find that lateral constraints imposed by the boundary between the active and inactive materials also inhibit the R to T transition. Phase-field calculations on both clamped and released PMN-PT thin films simulate our experimental findings. Resolving the suppression of thin film piezoelectric response is critical to their application in piezo-driven technologies.

A reconfigurable band-stop filter using piezoelectric-piezomagnetic superlattices with an external DC electric field

A novel reconfigurable band-stop filter using piezomagnetic-piezoelectric superlattices with the external direct-current (DC) electric field (PPSED) is presented. The center frequency of the forbidden band is reduced from to Hz in the band-stop filter as the thickness ratio of the piezoelectric domain to the piezomagnetic domain increases from to 9. The change of the forbidden bandwidth and the center frequency shows that the band-stop filter constructed by the PPSED is reconfigurable. The coupled polaritonic band structure is asymmetric with respect to the forward and backward directions and the forbidden bandwidth can be tuned by the DC electric field via the electro-optic effect. Unlike pure piezoelectric superlattices with the DC electric field, the forbidden bandwidth decreases with the increase of the electric field in the PPSED. The bandwidth tunability by the DC electric field can provide a guidance for the reconfigurable band-stop filter design to work in broadband frequencies.

Enhanced piezoresponse and surface electric potential of hybrid biodegradable polyhydroxybutyrate scaffolds functionalized with reduced graphene oxide for tissue engineering

Piezoelectricity is considered to be one of the key functionalities in biomaterials to boost bone tissue regeneration, however, integrating biocompatibility, biodegradability and 3D structure with pronounced piezoresponse remains a material challenge. Herein, novel hybrid biocompatible 3D scaffolds based on biodegradable poly(3-hydroxybutyrate) (PHB) and reduced graphene oxide (rGO) flakes have been developed. Nanoscale insights revealed a more homogenous distribution and superior surface potential values of PHB fibers (33 ± 29 mV) with increasing rGO content up to 1.0 wt% (314 ± 31 mV). The maximum effective piezoresponse was detected at 0.7 wt% rGO content, demonstrating 2.5 and 1.7 times higher out-of-plane and in-plane values, respectively, than that for pure PHB fibers. The rGO addition led to enhanced zigzag chain formation between paired lamellae in PHB fibers. In contrast, a further increase in rGO content reduced the α-crystal size and prevented zigzag chain conformation. A corresponding model explaining structural and molecular changes caused by rGO addition in electrospun PHB fibers is proposed. In addition, finite element analysis revealed a negligible vertical piezoresponse compared to lateral piezoresponse in uniaxially oriented PHB fibers based on α-phase ( P2 1 2 1 2 1 space group). Thus, the present study demonstrates promising results for the development of biodegradable hybrid 3D scaffolds with an enhanced piezoresponse for various tissue engineering applications. • PHB-rGO scaffolds with the enhanced 9.5 times surface potential and 2.5 times piezoresponse have been developed. • Surface electric potential and piezoelectric domain distributions in PHB-rGO fibers have been obtained. • A model explaining structural and molecular changes caused by rGO in PHB fibers is presented. • Piezoresponse of α-helical PHB structure in fibers is simulated.

An EFGM approach for permeable, semi-permeable and impermeable crack interaction study in 2D piezoelectric domains

This paper presents the numerical simulation of permeable, semi-permeable and impermeable crack interaction study in 2D piezoelectric domains using an element-free Galerkin method (EFGM). The electric and displacement fields are described by introducing the singularity terms into an approximation function. This study is performed with respect to effects of electrical loading, crack surface boundary conditions, crack orientation angles, aspect ratio and number of cracks in order to examine these effects on fracture parameters. Multiple inclined equidistant cracks are considered in piezoelectric domain under different crack surface boundary conditions. The proposed enrichment criterion accurately estimates fracture parameters which shows the robustness, efficacy and applicability of EFGM approach.