Piezoelectric Charge Research Articles

Interplay of surface polarization charge, dynamic electrical stimulation and compositional modification towards accelerated osteogenic response of NaxK1-xNbO3 piezo-bioceramics

Bone remodeling processes involve endogenous bioelectrical signals such as piezoelectric charges. Moreover, external electrical stimulation helps in improving the healing capability of injured tissues by modulating the metabolic signaling pathways of cells. Towards this end, the present study reveals the influence of the combined action of electrostatic surface polarization charge and dynamic pulsed electrical stimulation alongwith compositional modification towards improving the osteogenic response of emerging piezo-bioceramics, sodium potassium niobate [NaxK1-xNbO3 (x=0.2-0.8), NKN]. The dependence of crystal structure on compositions (x) was retrieved by Rietveld refinement and X-ray peak profile analyses. The surface charge, stored in the polarized (@ 25kV at 500°C) NaxK1-xNbO3 (x=0.2, 0.5, 0.8) samples were measured to be 0.52, 0.50 and 0.47μC/cm2, respectively, using thermally stimulated depolarized current (TSDC). X-ray photoelectron spectroscopy (XPS) survey scan spectra revealed that the polarization process does not alter the surface chemistry of NKN. Negatively charged surfaces are observed to accelerate early-stage adhesion of osteoblast-like cells which further results in enhanced spreading of adhered cells. Subsequently, the dynamic pulsed electrical stimulation of 1V/cm with the pulse duration of 400μs was applied, while the cells were being adhered on electrostatically charged surfaces. The quantitative and qualitative analyses revealed that the synergistic action of electrostatic surface polarization charge and dynamic pulsed electrical stimulation further accelerates cell proliferation and differentiation on negatively charged surfaces of Na and K-rich compositions of NKN. The mechanism of augmented cellular activity was analyzed using intracellular Ca2+ measurement.

Influence of chemically synthesized powder addition on K0.5Na0.5NbO3 ceramic’s properties

A new strategy to produce lead-free K0.5Na0.5NbO3 (KNN) piezoceramics with reliable and improved piezoelectric performance is presented for the first time. KNN powders were synthesized using two distinct synthesis routes: a mechanochemical activation-assisted solid-state route (KNNSSR) and a sol–gel modified Pechini method (KNNchem). KNNchem powders were mixed with KNNSSR at different weight ratios (0, 3, 5, 10 and 20 wt%), and the mixtures were conventionally consolidated and sintered at 1130 °C for 2 h. It was found that KNNchem powders influence crystal phase, microstructure and piezoelectric properties of the sintered pellets. Gradually increasing KNNchem content promotes the conversion of the undesired phase present in KNNSSR into the stoichiometric one. It is also proved that the addition of KNNchem between 5 and 10 wt% improves piezoelectric properties, eventually leading to a d33 piezoelectric charge constant value of 113–115 pC/N. These values are among the highest reported for undoped KNN ceramics obtained by conventional sintering.

Pulse-poling and characterization of (Na,K)NbO3 ceramics

Conventional direct current (DC)-poling and three different types of pulse-poling were performed on MnO-added Na0.55K0.45NbO3 (NKN) ceramics. While NKN with DC-poling at 4.0 kV mm−1 for a poling time (t p) of 100 s showed a piezoelectric charge coefficient d 33 of 141.3 pC N−1, an almost equivalent d 33 (141.3 pC N−1) was recorded by pulse-poling in only 10 s under a unipolar electric field of 4.0 kV mm−1, with either triangular, or rectangular waveform. Especially when applying a triangular waveform, d 33 was enhanced remarkably with increasing the number of pulse cycles. In contrast, NKN ceramics poled by alternating current (AC) electric field showed a d 33 of less than 135 pC N−1 under any condition. Polarization–electric (P–E) field responses, and domain structure observations via scanning electron microscopy, showed the different poling behaviors for the various poling techniques. These results suggested that the pulse-poling method under unipolar electric field is an efficient poling procedure for NKN ceramics.

Dielectric breakdown driven by flexoelectric and piezoelectric charge generation as hotspot ignition mechanism in aluminized fluoropolymer films

Using multiphysics simulations and experiments, we demonstrate that dielectric breakdown due to electric charge accumulation can lead to sufficient hotspot development leading to the initiation of chemical reactions in P(VDF-TrFE)/nAl films comprising a poly(vinylidene fluoride-co-trifluoroethylene) binder and nano-aluminum particles. The electric field (E-field) development in the material is driven by the flexoelectric and piezoelectric responses of the polymer binder to mechanical loading. A two-step sequential multi-timescale and multi-physics framework for explicit microscale computational simulations of experiments is developed and used. First, the mechanically driven E-field development is analyzed using a fully coupled mechanical–electrostatic model over the microsecond timescale. Subsequently, the transient dielectric breakdown process is analyzed using a thermal–electrodynamic model over the nanosecond timescale. The temperature field resulting from the breakdown is analyzed to establish the hotspot conditions for the onset of self-sustained chemical reactions. The results demonstrate that temperatures well above the ignition temperatures can be generated. Both experiments and analyses show that flexoelectricity plays a primary role and piezoelectricity plays a secondary role. In particular, the time to ignition and the time to pre-ignition reactions of poled films (possessing both piezoelectricity and flexoelectricity) are ∼10% shorter than those of unpoled films (possessing only flexoelectricity).

Piezoelectric charge induced hydrophilic poly(L-lactic acid) nanofiber for electro-topographical stimulation enabling stem cell differentiation and expansion

Cell-traction driven electrical stimulation on piezoelectric nanofibers mediates cell behavior without chemical factors or external stimuli, indicating a promising therapy at cell level. Generally, surface modification is required to achieve favorable cell adhesion for efficient electromechanical signal transmission. Nevertheless, common modification methodologies either easily fade away or destroy the nanostructure of piezoelectric nanofibers. Herein, with the assistance of ultrasound activated surface charges, in situ hydrophilic modification on piezoelectric poly(L-lactic acid) nanofibers is first proposed for cell adhesion. Due to the electrostatic interaction between dopamine and activated piezoelectric nanofiber, the efficient and robust in situ modification is obtained without compromising the nanofibrous structure. Stimulated by the piezoelectric nanofibers with modification, neural stem cells differentiate significantly into nerve cells on day 7 without exogenous growth factors. To our knowledge, the effect of inducing stem cell differentiation far outperforms that in previous reports. In addition, it has been demonstrated that the level of both cell differentiation and directional expansion is consistent with that of cell adhesion condition regardless of the intensity of electrical cue. This connection of cell adhesion and electro-topographical stimulation effects may guide the efforts in the design of electroactive scaffolds.

Properties of CNTs‐modified lead‐free BCTS ceramic–Portland fly ash cement composites

AbstractFly ash (FA) is widely used as a supplementary cementitious material in the production of Portland cement concrete. The effect of addition of carbon nanotubes (CNTs) and FA on the properties of barium calcium stannate titanate (BCTS) ceramic–Portland FA cement composites was investigated. These composites have potential for use as sensors and transducers in the monitoring of structural health in concrete structures containing FA. CNTs were found to have filled the pores of the composites. All composites showed good compatibility with the concrete mix. The dielectric constant and electrical conductivity of composites were in the range 200–257 and 1.04 × 10–6 to 1.66 × 10−6 S/m, respectively. The presence of FA in composites increased the piezoelectric voltage coefficient (g33). Adding CNTs increased the piezoelectric charge coefficient (d33), thickness electromechanical coupling coefficient (Kt), and also g33 but decreased mechanical quality factor (Qm), which is related to good for the receiving sensor and transducer application. CNTs can improve the properties of these composites and composite with FA content at 10 vol.%, and CNTs at 1 vol.% exhibited the highest compressive strength and piezoelectric values (d33 = 44 pC/N, g33 = 20.21×10–3 V m/N, and Kt = 18.9%), along with higher g33 values, than pure BCTS ceramic.

Influence of gate voltage dependent piezoelectric polarization on damage effect of GaN HEMT induced by high power electromagnetic pulse

In this paper, the influence of gate voltage dependent piezoelectric polarization on the damage effect of GaN HEMT induced by high power electromagnetic pulse was investigated in detail. Firstly, the necessity of considering gate voltage dependent piezoelectric polarization charge is stated theoretically. Secondly, by adding the polarization vector of z-axis PZPE, the modified polarization model is constructed. Then series of gate injection experiments were carried out with the help of TCAD simulation software to analysis the damage effect and the influence of gate voltage dependent piezoelectric polarization on the damage threshold of GaN HEMT caused by high power EMP. The results show that the threshold power and threshold energy of the device are reduced due to the temperature rise of the device becoming steeper at the same injected power and the damage time of the device shorter when considering the gate voltage dependent piezoelectric polarization. This conclusion is very important for device design using GaN materials especially when the device operates under high voltage conditions.

A new strategy for higher Td with large and temperature-independent d33 in BNT-based piezoceramics via quenching induced built-in field

One of the key challenges in the development of eco-friendly piezoceramics is to simultaneously get large piezoelectric charge coefficient d33 and high depolarization temperature Td in a facile and effective manner. In this study, we demonstrated that built-in field Eb caused by simple quenching in 0.93Bi0.5Na0.5TiO3-0.07BaTiO3 piezoceramic, which promoted the Td from 140 ℃ to 184 ℃ and accompanied by the superior thermal stability of real-time d33 (~140 ± 2.5pC/N) in a wide working temperature range of 25–170 ℃. Structural analyses illustrated that quenching induced spontaneous phase transition from tetragonal P4bm to rhombohedral R3c, which facilitated not only the development of Eb but also the increase of field-induced R3c phase ratio, thereby strengthening the stability of field-induced ferroelectric state. Thus, our work validated a simple and effective method for designing high-performance piezoelectric materials with increasing Td and temperature stability without sacrificing the large piezoelectric response.

Enhanced piezoelectricity in lead-free halide perovskite nanocomposite for self-powered wireless electronics

Lately, lead-free flexible piezoelectric nanogenerators (PENGs) have drawn much attention because of the threat posed by lead (Pb)-based piezoelectric materials to the environment. Here, we reported an organic-inorganic hybrid perovskites (OIHP) PENG, which is a combination of lead-free formamidinium tin (Sn) halide perovskite (CH(NH2)2SnBr3 (FASnBr3)) nanoparticles (NPs) and polydimethylsiloxane (PDMS) polymer matrix. By using piezoelectric force microscopy (PFM) measurements, we unveil the excellent piezoelectric properties of the FASnBr3 NPs with a high piezoelectric charge coefficient (d33) of ~ 50 pm/V. Due to the outstanding flexibility and uniform distribution properties, the device demonstrated a maximum piezoelectric peak to peak output voltage of 94.5 Vp-p, peak to peak current of 19.1 μAp-p, and output power density of 18.95 μW/cm2 with a tiny force of 4.2 N; these characteristics substantially outperform a number of the state-of-the-art halide perovskite based PENGs (Table S1). Given their high electromechanical energy conversion efficiency, the electrical energy produced from the PENGs was used to power a Bluetooth-capable system on chip (SoC) to build an entirely self-powered radio frequency (RF) communication system. For the first time, we established a self-powered RF wireless communication between nanogenerator and smart electronic devices which is solely based on a lead-free PENG. It is anticipated that the fabricated FASnBr3 @PDMS nanocomposite PENG not only possesses outstanding performance and reliability but also serves as a stepping-stone towards achieving self-powered Internet of Things (IoT) devices built using environment-friendly perovskite piezoelectric materials.

Detection of avian influenza virus H9N2 based on self-driving and self-sensing microcantilever piezoelectric sensor

In this article, we used the self-excitation and self-inductance characteristics of polyvinylidene fluoride (PVDF) piezoelectric materials, combined with the powerful signal processing and calculation analysis capabilities of integrated circuits, for the first time to explore a set of microcantilever sensor "readout system" without additional driver (self-driving) and can realize self-sensing external signal (self-sensing). It was successfully applied to the unlabeled detection of avian influenza virus (AIV) H9N2. The specific force of the antigen-antibody complexes on the surface of the microcantilever leads to the change of the stress of the cantilever, which drives the constructed detection device, and does not require an additional excitation source to drive it, that is, the self-driving part. At the same time, due to the movement of piezoelectric charges in the film caused by the positive piezoelectric effect of the PVDF film, self-inductive charges are generated on the surface of the sensor dielectric. The charge signal is converted into a voltage signal, and the sensing part is completed, that is, self-sensing. The immunosensor has a linear range of 100-1000 ng/mL with a detection limit of 2.9 ng/mL. The method will also open up a new avenue for the detection of other analytes based on antigen-antibody responses.

Realization of flexible AlGaN/GaN HEMT by laser liftoff

We demonstrate fully fabricated AlGaN/GaN high electron mobility transistors (HEMTs) transferred from sapphire to copper tape on flexible polyethylene terephthalate using 193 nm excimer laser liftoff (LLO). The heterojunction is structurally intact after LLO, leading to preserved electron mobility ∼1630 cm2 V−1 s−1 and carrier concentration ∼1013 cm−2. The maximum drain saturation current decreased by ∼18% after transfer, which is a lower reduction than other reported transfer methods. The drain current of this flexible HEMT increased monotonically under tensile stress applied using a convex-shaped plate, while the threshold voltage shifted more negative in quantitative agreement with the expected piezoelectric charge for an intact heterojunction.

Piezoelectric properties and related parameters of novel 1–2–2 composites based on single crystals of the PZN–xPT type

High-performance 1–2–2 composites based on domain-engineered relaxor-ferroelectric single crystals are analyzed, which demonstrate strong electromechanical coupling and large energy-harvesting characteristics. The role of the single-crystal rods and laminar polymer matrix is highlighted. A large anisotropy of the piezoelectric charge coefficients d 3j* and electromechanical coupling factors k 3j* is observed in specific volume-fraction ranges, with proposed dependence diagrams. The effective parameters of composites with parallelepiped-shaped rods are compared to similar parameters for composites based on cylindrical rods, with good agreement between parameters. These novel composites can be used in piezoelectric sensors, actuators, transducers, and energy-harvesting devices.

Polarization-dominated thermal-electric-mechanical behaviours in GaN ceramics

In this paper, we have systematically investigated the polarization-dependent thermal-electric-mechanical behaviours in GaN piezoelectric semiconductor ceramics (PSCs). A thermo-piezoelectric semiconductor model is proposed with pyroelectric and thermoelastic as well as piezoelectric couplings. It is shown that polarization has a non-negligible influence on the thermoelectric properties of GaN ceramics. Because the potential barrier caused by pyroelectricity near the hot end suppresses the Seebeck effect, the thermoelectric potential and current of polarized samples obviously decrease with temperature difference. Moreover, it is the intercoupling between pyroelectric polarization and piezoelectric charges that largely affects the bending strength of GaN ceramics. Compared with the ordinary ceramics, the electromechanical and thermoelectric properties of GaN PSCs can be dominated through polarization.

Study on piezo-phototronic effect of AlZnO thin film flexible ultraviolet photodetector

In this research, AlZnO (AZO) flexible ultraviolet (UV) photodetectors (PDs) with piezo-phototronic effect were fabricated by radio frequency (RF) magnetron sputtering. AZO has the advantages of low-cost synthesis and relatively high light response in the UV region. By changing the thickness of the AZO film, the carrier density obtained in the AZO film is adjusted. In the AZO film with lower carrier density, piezoelectric polarization charges (piezo-charges) are easily exposed. Under the action of the piezo-phototronic effect, the photocurrent and responsivity of the two groups of AZO thin film PDs with growth times of 10 min and 20 min increased, and the maximum response increased by 286% and 143%, respectively. This broadens the application range of ZnO-based composite materials.

Piezodeposition of Metal Cocatalysts for Promoted Piezocatalytic Generation of Reactive Oxygen Species and Hydrogen in Water

AbstractPiezocatalysis in aqueous medium has shown great potential for various applications, however the efficiency of piezocatalytic nanoparticles is harmed by the limited utilization of piezoelectric charge and the lack of active catalytic interface. In this study, BaTiO3@Metal (BTO@M, M=Pt, Pd and Au) hetero‐nanostructures were synthesized by using a piezodeposition method. The deposited metal cocatalysts significantly promote the separation and migration of piezogenerated charge, consequently enhancing the piezocatalytic reactions on different metal cocatalyst interfaces. Specifically, BTO@Au under ultrasonic vibrations exhibited most efficient generation of reactive oxidative species via a two‐electron reduction pathway in the presence of dissolved oxygen, while BTO@Pt showed promoted hydrogen evolution in the absence of oxygen. The metal‐piezoelectric hetero‐nanostructures proposed in this work highlight the key role of noble metal as cocatalysts for piezoelectricity‐driven oxygen reduction and hydrogen evolution reactions, which could further advance piezocatalysis in the field of clean energy, water disinfection and biomedicine.

Comparative investigation into polarization field-dependent internal quantum efficiency of semipolar InGaN green light-emitting diodes: A strategy to mitigate green gap phenomenon

Semipolar InGaN-made green light-emitting diodes (LEDs) have sparked tremendous interest within the photonics community in recent past as advantageous replacements for already operable polar (0001)-oriented LEDs due to reduction in efficiency droop and related green gap phenomenon. Nevertheless, any theoretical investigation in order to compare internal quantum efficiency (IQE); output power and 3 dB bandwidth (BW) within non-c-plane-oriented InGaN green LEDs is innately unavailable. This study intends to describe the consequence of strain-induced polarization field on aforesaid major optical and electronic characteristics of In0.29Ga0.71N/GaN green LED along semipolar (101̅2), (112̅2), (101̅1), (202̅1), (303̅1̅), (202̅1̅) and (101̅1̅) crystal orientations by introducing modified ABC model which involves the contribution from phase-space filling (PSF) and carrier drift leakage. Our numerical investigation illustrates that best IQE, droop ratio, light emission spectra, output power and I-V profile can be obtained from (112̅2)-oriented InGaN green LED due to inconsiderable appearance of intrinsic plus lattice-mismatch induced piezoelectric polarization charge. 3 dB BW and differential carrier lifetime (DLT) is also shown to be superior for this green LED structure. In addition with these, the evidence noticed from verification of external quantum efficiency (EQE) with previous experimental reports on semipolar (112̅2) InGaN green LEDs indicates reasonable accuracy of our theoretical approach.

Piezoelectric voltage constant and sensitivity enhancements through phase boundary structure control of lead-free (K,Na)NbO3-based ceramics

The piezoelectric voltage constant (g33) is a material parameter critical to piezoelectric voltage-type sensors for detecting vibrations or strains. Here, we report a lead-free (K,Na)NbO3 (KNN)-based piezoelectric accelerometer with voltage sensitivity enhanced by taking advantage of a high g33. To achieve a high g33, the magnitudes of piezoelectric charge constant d33 and dielectric permittivity εr of KNN were best coupled by manipulating the intrinsic polymorphic phase boundaries effectively with the help of Bi-based perovskite oxide additives. For the KNN composition that derives benefit from the combination of εr and d33, the value of g33 was found to be 46.9 × 10−3 V·m/N, which is significantly higher than those (20 – 30 × 10−3 V·m/N) found in well-known polycrystalline lead-based ceramics including commercial Pb(Zr,Ti)O3 (PZT). Finally, the accelerometer sensor prototype built using the modified KNN composition demonstrated higher voltage sensitivity (183 mV/g) when measuring vibrations, showing a 29% increase against the PZT-based sensor (142 mV/g).

Effect of calcium substitution on structural, dielectric, ferroelectric, piezoelectric, and energy storage properties of BaTiO3

The effect of calcium substitution on the structural, dielectric, ferroelectric, piezoelectric, and energy storage properties of BaTiO3 (BT) ceramics has been investigated. XRD confirmed the phase formation of Barium Calcium Titanate (BCT), and structural Rietveld refinement was used to estimate the lattice parameters. It is evident from the SEM data that the average grain size decreases as calcium is added. At Curie temperature (110 °C), BCT 0.10 ceramic has a good dielectric constant of 15834 and a very low dielectric loss of 0.009. According to the ferroelectric and piezoelectric investigations, BCT 0.10 exhibits maximum spontaneous polarization with the highest piezoelectric charge coefficient of 100 pC/N. BCT 0.10 has a maximum energy storage density of 96.8 mJ/cm3 and a good energy storage efficiency of 53.9%, which is around three times that of pure BaTiO3. These results suggest that the BCT ceramic has good potential for energy storage applications.

Optimizing energy harvesting performance by tailoring ferroelectric/relaxor behavior in KNN-based piezoceramics

Piezoelectric energy harvesters (PEHs) fabricated using piezoceramics could convert directly the mechanical vibration energy in the environment into electrical energy. The high piezoelectric charge coefficient (d33) and large piezoelectric voltage coefficient (g33) are key factors for the high-performance PEHs. However, high d33 and large g33 are difficult to simultaneously achieve with respect to g33 = d33/(ε0εr) and d33 = 2Qε0εrPr. Herein, the energy harvesting performance is optimized by tailoring the CaZrO3 content in (0.964−x)(K0.52Na0.48)(Nb0.96Sb0.04)O3 −0.036(Bi0.5Na0.5)ZrO3−xCaZrO3 ceramics. First, the doping CaZrO3 could enhance the dielectric relaxation due to the compositional fluctuation and structural disordering, and thus reduce the domain size to ∼30 nm for x = 0.006 sample. The nanodomains switch easily to external electric field, resulting in large polarization. Second, the rhombohedral–orthorhombic–tetragonal phases coexist in x = 0.006 sample, which reduces the polarization anisotropy and thus improves the piezoelectric properties. The multiphase coexistence structures and miniaturized domains contribute to the excellent piezoelectric properties of d33 (354 pC/N). Furthermore, the dielectric relative permittivity (εr) reduces monotonously as the CaZrO3 content increases due to the relatively low ion polarizability of Ca2+ and Zr4+. As a result, the optimized energy conversion coefficient (d33 × g33, 5508 × 10−15 m2/N) is achieved for x = 0.006 sample. Most importantly, the assembled PEH with the optimal specimen shows the excellent output power (∼48 µW) and lights up 45 red commercial light-emitting diodes (LEDs). This work demonstrates that tailoring ferroelectric/relaxor behavior in (K,Na)NbO3-based piezoelectric ceramics could effectively enhance the electrical output of PEHs.

A high-performance, single-electrode and stretchable piezo-triboelectric hybrid patch for omnidirectional biomechanical energy harvesting and motion monitoring

Triboelectric nanogenerators (TENGs) have recently drawn much attention in the field of biomechanical energy harvesting and motion monitoring. However, the electrode stretchability and contact-separation model induced complicated packed structure remain a problem that heavily affects output performance during various human movements and requires to be urgently addressed. Here, a single-electrode piezo-triboelectric hybrid nanogenerator (SEP-TENG) integrated with stretchable liquid-metal metal electrodes is reported, which simultaneously achieves outstanding energy harvesting performance and skin-comfort human motion monitoring. A polarized piezoelectric BaTiO3/silicon rubber (SR) composites film is served as the effective negative tribomaterial, benefiting from the improved dielectric constant and piezoelectric charge transfer, the optimized SEP-TENG generates a high peak power density of 5.7 W/m2 while contacted with human skin. Besides, owing to the ultralow Young's modulus of the SR encapsulation layer and tribo-piezoelectric hybrid layer, the homogeneous integrated multilayer composite serves no break till a 745% elongation, promoting that the SEP-TENG could effectively harvest biomechanical energy and realize stable power supplying for wearable electronics even under large deformation state. Furthermore, the SEP-TENG could comfortably attach to the finger joints and collect bending energy. This work provides a novel design methodology for a single-electrode TENG to realize omnidirectional biomechanical energy harvesting and motion monitoring.