Effective Piezoelectric Constant Research Articles

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

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

Tailorable piezoelectric and flexoelectric output of a polymer-particle composite

Materials with different combinations of piezoelectric and flexoelectric properties offer multifunctionality and versatility in terms of modes of operation in sensing, actuation, and energy harvesting. We explore a microscopic mechanism for tailoring the macroscopic quasi-static mechanoelectrical output of polymer-particle composites by taking advantage of heterogeneity-induced enhancement of the stress fields and strain gradient fields. The idea focuses on using microscopic inclusions, such as embedded particles and voids, to manipulate the activation and relative contributions of the piezoelectric and flexoelectric effects under different modes of mechanical excitation, such as uniaxial compression and flexural bending. The material system studied is a composite of poly(vinylidene fluoride-co-trifluoroethylene [P(VDF-TrFE)] polymer and nanoaluminum (nAl) particles, or P(VDF-TrFE)/nAl. This system is interesting because P(VDF-TrFE) exhibits both piezoelectric and flexoelectric behaviors and nAl particles have significantly higher elastic stiffness than the polymer. A range of piezoelectric and flexoelectric properties of P(VDF-TrFE) and the stiffness of the particles are considered. Significant microstructural effects are found to enable tailoring of the mechanoelectrical response through microstructure variation. The responses of the composite are quantified using the effective piezoelectric constant (d33,effo) and the effective flexoelectric coefficient (μTR,effo). It is found that the effective macroscopic piezoelectric and flexoelectric behaviors can be changed either independently or simultaneously through different combinations of microstructure attribute changes. The mechanism revealed points out avenues for developing materials with tunable mechanoelectrical behaviors and multifunctionality.

Ferroelectric Polarization‐Enhanced Performance of Flexible CuInP2S6 Piezoelectric Nanogenerator for Biomechanical Energy Harvesting and Voice Recognition Applications

Abstract2D piezoelectric materials have strong intrinsic piezoelectricity and superior flexibility, which are endowed with huge potential to develop piezoelectric nanogenerators (PENGs). However, there are few attempts to investigate the energy harvesting of 2D ferroelectric materials. Herein, an enhanced output performance is reported by ferroelectric polarization in a PENG with exfoliated 2D ferroelectric CuInP2S6 (CIPS). Specifically, the polarized CIPS‐based PENG produces a short‐circuit current of 760 pA at 0.85% tensile strain, which is 3.8 times higher than that of unpolarized CIPS‐based PENG. Systematical PFM and Raman analysis reveal that the ferroelectric polarization remarkably reinforces the effective piezoelectric constant of CIPS nanoflakes and boosts the in‐plane migration and out‐of‐plane hopping of copper ions, which is the main reason for the enhancement of output performance. Furthermore, the CIPS‐based PENG can not only be utilized to harvest biomechanical energy such as wrist joints movement, but also exhibits a potential for a voice recognition system integrated with deep learning technology. The classification accuracy of a series of letter sounds is as high as 96%. This study commendably broadens the application scope of 2D materials in micro‐nano energy and intelligent sensors, which will have profound implications for exploring wearable nanoelectronic devices.

Sliding ferroelectricity in van der Waals layered γ-InSe semiconductor

Two-dimensional (2D) van-der-Waals (vdW) layered ferroelectric semiconductors are highly desired for in-memory computing and ferroelectric photovoltaics or detectors. Beneficial from the weak interlayer vdW-force, controlling the structure by interlayer twist/translation or doping is an effective strategy to manipulate the fundamental properties of 2D-vdW semiconductors, which has contributed to the newly-emerging sliding ferroelectricity. Here, we report unconventional room-temperature ferroelectricity, both out-of-plane and in-plane, in vdW-layered γ-InSe semiconductor triggered by yttrium-doping (InSe:Y). We determine an effective piezoelectric constant of ∼7.5 pm/V for InSe:Y flakes with thickness of ∼50 nm, about one order of magnitude larger than earlier reports. We directly visualize the enhanced sliding switchable polarization originating from the fantastic microstructure modifications including the stacking-faults elimination and a subtle rhombohedral distortion due to the intralayer compression and continuous interlayer pre-sliding. Our investigations provide new freedom degrees of structure manipulation for intrinsic properties in 2D-vdW-layered semiconductors to expand ferroelectric candidates for next-generation nanoelectronics.

Influence of AlN/ScAlN piezoelectric multilayer on the electromechanical coupling of FBAR

Based on the truth, the electromechanical coupling in the top and bottom Mo electrodes caped AlN can be enhanced by replacing the Sc doped AlN (ScAlN). We tune the electromechanical coupling (kt2) of the film bulk acoustic resonator (FBAR) by varying the thickness ratio in AlN and ScAlN piezoelectric multilayer. We found that the electromechanical coupling of the piezoelectric-multilayer FBAR is area size dependent. In order to investigate the multilayer electromechanical coupling in various thickness ratios, we propose a theory to simulate both materials piezoelectric constants e varying with the area size. In various thickness ratios, the effective piezoelectric constant of the AlN layer increases with the area of FBAR, but the ScAlN layer exhibits an optimal piezoelectric constant in increasing area. Eventually, we realized that increasing the significant piezoelectric constant is inevitable for reducing the size of FBARs.

Modified Stranski-Krastanov Growth of Amino Acid Arrays toward Piezoelectric Energy Harvesting.

Biomolecule-based piezoelectric nanostructures emerged as a new class of energy-converse materials, and designing tailored piezoelectric amino acid arrays is essential to achieve efficient electrical-mechanical coupling and fulfill their application potential. However, the controlled growth of amino acid nanostructures is still challenging due to the limited understanding of their growth mechanism. Herein, we base on the Stranski-Krastanov (S-K) growth mode and propose a mechanism for the growth of ordered amino acid array structures via physical vapor deposition. The growth of vertical valine sheet arrays is examined by changing the substrate temperature, chamber pressure, and source-substrate distance, and a "layer-plus-sheet" growth process is revealed. The modified S-K growth mode is applied to fabricate other amino acid nanostructures like leucine and isoleucine. The growth mode not only explains the formation of uniform and controllable morphology of amino acid structures but also leads to the significant enhancement of their piezoelectric properties. The maximal effective piezoelectric constant of valine sheets is 11.4 pm V-1, which approaches its highest predicted value. The output voltage of the valine array-based nanogenerator is ∼4.6 times the output voltage of the valine powder-based nanogenerator. This work provides new insights into the growth mechanism of ordered piezoelectric amino acid arrays, making them promising candidates for applications in wearable or implantable electronic devices.

Electrical cycling of Cu-PMNZT multilayer co-fired ceramic actuators

The electric cycling characteristics of Cu/0.2(PbMg1/3Nb2/3O3)-0.8(PbZr0.475Ti0.525O3) (PMNZT) multilayer ceramic actuators were investigated. Cu/PMNZT co-fired multilayer actuators were fabricated by conventional tape casting, lamination, and sintering at 950 °C in air with subsequent annealing at 225 °C or 400 °C under a hydrogen atmosphere. In such processes, annealing of the multilayer samples under a reducing atmosphere is an important factor in controlling the piezoelectric performance. Unipolar and bipolar electric fields were applied to the actuators to investigate the fatigue behavior of the multilayer ceramic actuators. The sample annealed at 400 °C showed significant degradation in the effective electromechanical coupling coefficient (keff) and dynamic piezoelectric constant (d33*) after 1 × 108 electrical cycles, while the sample annealed at 225 °C showed less degradation. X-ray diffraction and X-ray photoelectron spectroscopy analyses were performed to evaluate the difference in crystalline structures as a function of annealing temperature. The keff, d33*, polarization, and strain were measured and evaluated as a function of the number of cycles. The cyclic dependence of strain was fitted to a linear logarithmic stretched exponential law. The significant degradation of the sample annealed at 400 °C is attributed to the reorientation of oxygen vacancies formed upon annealing, which gives a rise to internal field in the ceramic layer. The degraded performance of cycled sample was refreshed by a heating at 500 °C in air.

No‐Heating Deposition of 1‐μm‐Thick Y‐Doped HfO2 Ferroelectric Films with Good Ferroelectric and Piezoelectric Properties by Radio Frequency Magnetron Sputtering Method

Y‐doped HfO2 ferroelectric films of ≈1 μm thick are deposited without heating by a radio frequency magnetron sputtering method. {100}‐oriented epitaxial films with orthorhombic phase are grown on (100)ITO//(100)YSZ substrates without heating. Their crystal structure is almost unchanged after postheat treatment at 800 °C. Ferroelectricity is confirmed for the no‐heating‐deposited films by polarization−electric field (P−E) curves, and their remanent polarization (Pr) and coercive fields are 12 μC cm−2 and 1.5 MV cm−1, respectively. These values are also almost unchanged after the postheat treatment. However, the postheat‐treated films show a lower breakdown electric field compared to the as‐deposited films without heat treatment. Approximately 1 μm‐thick films are also prepared without heating on (111)ITO/(111)Pt/TiOx/SiO2/(100)Si and (111)Pt/TiOx/SiO2/(100)Si substrates. Almost pure orthorhombic/tetragonal phase is deposited on both substrates without heating. The Pr value of the film on the (111)ITO/(111)Pt/TiOx/SiO2/(100)Si substrate is about 1.5 times larger than that on the (111)Pt/TiOx/SiO2/(100)Si substrate due to the better crystallinity of the film lattice‐matched with the underlying ITO layer. The effective piezoelectric constant (d33,f) of the film deposited on the (111)ITO/(111)Pt/TiOx/SiO2/(100)Si substrate without heating is estimated to be 4 pm V−1. The present low process temperature leads us to expect novel applications, especially for low‐heat‐resistance applications.

Polar-axis-oriented epitaxial tetragonal (Bi,K)TiO3 films with large remanent polarization deposited below Curie temperature by a hydrothermal method

A hydrothermal method was used to epitaxially grow 70-nm-thick tetragonal (Bi,K)TiO3 films with stoichiometric compositions at 240 °C on (001)cSrRuO3//(001)SrTiO3 substrates. Crystal structure analysis revealed that the obtained (Bi,K)TiO3 films had a polar-axis orientation attributable to the matching of the in-plane lattice with the SrRuO3 underlayer. Large coherent displacement of A-site ions along the polar direction observed by transmission electron microscopy may have induced the large tetragonal distortion of c/a = 1.046. The dielectric constant was about 100 and was almost frequency independent in the range of 103–105 Hz, while the dielectric loss, tan δ, was below 5%. Well-saturated ferroelectric polarization−electric field (P−E) hysteresis loops were observed, and the remanent polarization (Pr) was 84 μC/cm2. In addition, the effective piezoelectric constant, d33,eff., was estimated to be 85 pm/V by time-resolved x-ray diffraction measured under an applied electric field. The Pr and d33,eff. values were larger than those reported for polar-axis-oriented epitaxial tetragonal Pb(Zr0.35Ti0.65)O3 films, indicating that the polar-axis-oriented tetragonal (Bi,K)TiO3 film has high potential as a lead-free material for various applications. Specifically, the small εr and large d33,eff. led to an improvement in the figures of merit [d33,eff./εr and (d33,eff.)2/εr], the most important index in sensor and energy-harvester applications.

Towards high-performance linear piezoelectrics: Enhancing the piezoelectric response of zinc oxide thin films through epitaxial growth on flexible substrates

Ferroelectrics are popular for sensors, actuators and transducers. However, the energy barrier for reversing the polarization leads to extra energy losses, while the hysteresis causes phase-lags and non-linearities between input and output signals. The high piezoelectric constants of ferroelectrics dictate the figure-of-merit of piezoelectric devices. Enhancing the piezoelectric constant of linear-piezoelectrics potentially leads to next-generation piezoelectric devices free from issues associated with ferroelectrics. By epitaxial growth of undoped ZnO films on flexible Hastelloy substrates, we demonstrated an ~85% improvement in the piezoelectric constant, and more importantly maintained the linearity of the piezoelectric response. Strong out-of-plane and in-plane crystallographic alignments are detected in the epitaxial sample, yet modeling of the effective thin-film piezoelectric constant shows only a limited contribution of the optimized textures. The improvement in the piezoelectric response is ascribed mostly to the in-plane epitaxial strain resulted from the lattice mismatch of ZnO to the substrate. The epitaxial ZnO film on Hastelloy promisingly offer high-precision positioners with nano-/pico-meter resolutions. Enhancing the piezoelectric constant by strain engineering potentially removes the barrier for applications of linear-piezoelectrics and enriches the piezoelectric research community.

Numerical simulation of electromechanical coupling properties of three-dimensional braiding piezoelectric composite actuator

In this paper, an innovative three-dimensional braiding piezoelectric composite actuator (3D-BPCA) is proposed. Based on the 3D braiding technology, the geometric model and representative volume unit (RVU) model of the 3D-BPCA are established. The effective elastic constant, dielectric constant and piezoelectric constant of the braiding piezoelectric composite layer (BPCL) are predicted. The electromechanical properties of the 3D-BPCA under the electromechanical coupling field is theoretically analyzed and numerically simulated, and compared with the piezoelectric ceramics actuator (PZT-5A). Numerical results show that the 3D-BPCA has better actuating properties than the PZT-5A and has a wide application prospects.

Research and development of high temperature multilayer piezo stack based on Na0,5Bi4,5Ti4O15 lead-free ceramic system produced by tape-casting slurry technology

Multilayer piezo stack based on Na0,5Bi4,5Ti4O15 was produced by tape casting slurry technology. X-ray diffraction, dielectric permittivity, piezoelectric and pyroelectric studies have been performed on the specimens. It was established that specimens have a textured structure due to the orientation of basal planes (001) plate-like grains parallel to the direction of film casting. The Curie point (Tc = 645 °C) of the obtained stacks have been determined from the temperature-frequency dependences of the dielectric permittivity and loss tangent, it is established that they have a relatively high effective piezoelectric constant (d33*= 180 pC/N) for NBT based ceramic system. In concluding it has been analyzed the prospect of the specimens in high temperature applications.

Effects of starting materials on the deposition behavior of hydrothermally synthesized {1 0 0}c-oriented epitaxial (K,Na)NbO3 thick films and their ferroelectric and piezoelectric properties

Epitaxial (K0.88Na0.12)NbO3 films were deposited at 240 °C onto (1 0 0)cSrRuO3//(1 0 0)SrTiO3 substrates utilizing a hydrothermal method. Both crystalline and amorphous niobium oxide powders were utilized as starting niobium sources with KOH and NaOH as potassium and sodium sources, respectively. Film thickness increased with deposition time, but eventually became saturated. The saturated film thickness of (K0.88Na0.12)NbO3 films prepared from the amorphous niobium source was greater than that from the crystalline source for mixtures of 6 and 7 mol/L KOH-NaOH solutions. This is found to be due to the suppression of the (K,Na)NbO3 powder simultaneously prepared with films by selecting amorphous niobium source. Their electrical and piezoelectric properties were nearly identical after following heat treatment at 600 °C for 10 min in an atmospheric O2 flow irrespective of the starting niobium sources; The average values of remanent polarization and effective longitudinal piezoelectric constant, d33, were 5–6 μC/cm2 and 45 pm/V, respectively.

Growth orientation-related enhancement of electrical properties in (Na0.85K0.15)0.5Bi0.5TiO3-based composite films

TiO2-coated (Na0.85K0.15)0.5Bi0.5TiO3 (NKBT) composite films with thicknesses of 250 nm and 650 nm are synthesized on Pt(111)/Ti/SiO2/Si using an aqueous sol-gel method. X-ray diffraction (XRD) in ω-scan and ψ-scan modes is performed to study the crystal orientation of the films. The electrical properties of the TiO2-coated NKBT composite films are investigated over a temperature range from -150 °C to150 °C. Compared to films without the TiO2 layer, the TiO2-coated NKBT films exhibit enhanced electrical properties, higher temperature stability, and better endurance performance, which can be ascribed to the combined effects of the highly (100)-preferred orientation and improved degree of crystallization. The composite film in which TiO2 layers are attached on both sides of the 650 nm-thick NKBT film demonstrates the best ferroelectric performance with the highest remnant polarization (Pr) of 24.2(±1.2) μC/cm2 under 750 kV/cm, the best piezoelectric performance with the highest effective piezoelectric constant (d33*) of 82(±4) pm/V, and the best electric performance with the lowest leakage current density of 4.5 × 10−6(±0.4 × 10−6) A/cm2 at 20 V. Piezoresponse force microscopy (PFM) further confirms the enhanced ferroelectricity and domain switching of the TiO2-coated composite films on a microscopic scale. In addition, the Pr values of the films increase gradually as the temperature decreases from 150 °C to-150 °C, while the d33* values exhibit the opposite trend, which is mainly attributed to the suppressed mobility of thedomain walls at low temperatures.

Thickness-dependent structural and electromechanical properties of (Na0.85K0.15)0.5Bi0.5TiO3 multilayer thin film-based heterostructures

(Na0.85K0.15)0.5Bi0.5TiO3 (NKBT) multilayer thin films with different thicknesses of 100–700nm, corresponding to 2–14 layers with each layer of ~50nm thickness, are synthesized on Pt(111)/Ti/SiO2/Si substrates to form Pt/NKBT/Pt/Ti/SiO2/Si heterostructures using different spin-coating and annealing conditions in a modified aqueous sol-gel process. The multilayer thin films spin-coated by two steps (step 1/2) at 600/4000rpm for 6/30s and annealed at 700°C for 5min with a heating rate of 30°C/s show a dense, uniform, and continuous morphology as well as a pure perovskite structure with a rhombohedral–tetragonal phase transition at ~140°C and no preferential orientation in the heterostructures. Their structural and electromechanical properties exhibit consistent improvement trends with increasing thickness from 100 to 550nm (i.e., 2–11 layers). The 550nm-thick, 11-layer films demonstrate the best ferroelectric, dielectric, piezoelectric, and electric performance in terms of the highest remnant polarization, saturation polarization, dielectric constant, and effective piezoelectric constant of 18.3μC/cm2, 53.6μC/cm2, 463, and 64pm/V, as well as the lowest coercive field, dielectric loss tangent, and leakage current density of 116kV/cm, 0.057, and 27μA/cm2, respectively. The observed thickness-dependent improvement is explained by an interfacial passive layer effect where the motion of both 180° and non-180° domain walls is enhanced in the thicker multilayer thin films by weakening the influence of domain pinning in the interfacial passive layers between the multilayer thin films and the substrates.

Multiferroic BiFeO3 thin films and nanodots grown on highly oriented pyrolytic graphite substrates

Multiferroic BiFeO3 (BFO) thin films and nanodots are deposited on highly oriented pyrolytic graphite (HOPG) substrates via a pulsed laser deposition technique, where the HOPG surface has a honeycomb lattice structure made of carbon atoms, similar to graphene. A graphene/BFO/HOPG capacitor exhibited multiferroic properties, namely ferroelectricity (a residual polarization of 26.8 μC/cm2) and ferromagnetism (a residual magnetization of 1.1 × 10−5 emu). The BFO thin film had high domain wall energies and demonstrated switching time of approximately 82 ns. An 8-nm BFO nanodot showed a typical piezoelectric hysteresis loop with an effective residual piezoelectric constant of approximately 110 pm/V and exhibited two clearly separated current curves depending on the ferroelectric polarization direction.

Characterization of piezoelectric ceramics using the burst/transient method with resonance and antiresonance analysis

AbstractIn this paper, a comprehensive methodology for characterizing the high power resonance behavior of bulk piezoelectric ceramics using the burst method is described. In the burst method, the sample is electrically driven at its resonance frequency, and then either a short circuit or an open circuit condition is imposed, after which the vibration decays at the resonance or antiresonance frequency, respectively. This decay can be used to measure the quality factor in either of these conditions. The resulting current in the short circuit vibration condition is related to the vibration velocity through the “force factor.” The generated voltage in the open circuit vibration condition corresponds to the displacement by the “voltage factor.” The force factor and the voltage factor are related to material properties and physical dimensions of the sample. Using this method, the high power behavior of the permittivity, compliance, effective piezoelectric charge constant, electromechanical coupling factor, and material losses can be determined directly by measuring the resonance (short circuit) and antiresonance (open circuit) frequencies, their corresponding quality factors, the force factor A, and the voltage factor B. The experimental procedure to apply this method is described and demonstrated on commercially available hard and semi‐hard PZT materials of geometry.

Orientation control of SrRuO3 thin film on a Si substrate by chemical solution deposition for an electrode of lead zirconate titanate thin films

A strontium ruthenium oxide (SRO) electrode was deposited on a Si substrate using chemical solution deposition (CSD). For this study, the crystal orientation of the SRO electrode was controlled using a CSD-derived seeding layer deposited on a Si substrate. Thereby, SRO thin film with a-axis preferred orientation was obtained on the Si substrate. Furthermore, lead zirconate titanate (PZT) thin film with Zr/Ti=50/50 composition (PZT50) was deposited onto the a-axis oriented SRO layer. The deposited PZT thin film also exhibited preferred orientation in the direction of the a-axis and c-axis. The estimated remanent polarization and the effective piezoelectric constant (d33eff) were, respectively, 20μC/cm2 and 298pm/V. These values were nearly equal to those of the reported bulk PZT of the same composition.

Green paper-based piezoelectronics for sensors and actuators

We report a novel biodegradable piezoelectric composite fabricated from paper and the piezoelectric salt, sodium potassium tartrate tetrahydrate (Rochelle salt, which we term PiezoSalt). The piezoelectric composite is non-toxic and is fabricated free of environmentally harmful solvents by impregnating PiezoSalt into a paper matrix through the crystallization of a concentrated PiezoSalt brine solution. The composite exhibits an effective piezoelectric constant between 3 and 25 pCN−1, dielectric constant of 7, mass density of 625kgm−3, and a Young’s modulus between 7 and 8GPa. When directly actuated, cm-scale cantilevers consisting of PiezoSalt paper produced clearly audible sound waves, illustrating one potential application. PiezoSalt paper composite provides a scalable, high throughput approach for biodegradable sensors and transducers with unsurpassed environmentally friendly processing.

A conceptual study on the dynamics of a piezoelectric MEMS (Micro Electro Mechanical System) energy harvester

The mechanical behavior of a bimorph piezoelectric micro cantilever exposed to harmonic base excitation is investigated. The governing motion equation coupled with the equation of the output electrical circuit is discretized using Galerkin method and numerically integrated over the time. Two different types of output circuits including parallel and series connections are examined and the most effective output circuit from the power delivery point of view on the domain of the governing parameters is introduced. The energy conservation is examined by comparing the input and harvested energies. It is concluded that the energy harvesting in the absence of mechanical damping resembles the behavior of a damped mechanical oscillator due to the exponential attenuation of the motion amplitude. It is shown that the output power in terms of the load resistance of the output circuit, exhibits Lorenzian behavior revealing the multi factorial dependency of the power on the governing parameters. The effect of load resistance and the effective piezoelectric stress constant on the equivalent damping ratio is investigated. Subjected to harmonic base excitation, the steady state voltage, current and power responses are presented. The results are presented for various piezoelectric materials and on the plane of load resistance and effective piezoelectric stress constant, the output power delivery as well as the equivalent non-dimensional damping coefficient is determined.