Piezoelectric Coefficient Research Articles

On the Piezoelectric Properties of Zinc Oxide Thin Films Synthesized by Plasma Assisted DC Sputter Deposition

AbstractThis work presents a study of piezoelectric zinc oxide (ZnO) thin films deposited by a novel post‐reactive sputtering method. The process utilizes a rotating drum with DC magnetron sputtering deposition onto substrates with subsequent DC plasma‐assisted oxidation of the deposited metal to metal oxide. The paper analyzes the influence of plasmaassisted magnetron sputtering (PA‐MS) deposition parameters (O2 plasma source power, O2 flow, and Ar flow) on the morphological, structural, optical, and piezoelectric properties of ZnO thin films. Design of experiments has been utilized to evaluate the role of these parameters on the growth rate (rg) and the properties of resulting films. Results indicate a predominant influence of the plasma power on the rg over other parameters. Among the eight tested samples, three of them show high crystal quality with high intensity (0001) diffraction peak, characteristic of the wurtzite crystalline structure of ZnO, and one of them exhibits piezoelectric coefficient values of ≈11pC N−1. That sample corresponding to a ZnO film deposited at the lowest rg of 0.075 nm s−1, confirmed the key role of the deposition parameters on the piezoelectric response of films, and demonstrated PA‐MS as a promising technique to produce high‐quality piezoelectric thin films.

Large out-of-plane piezoelectric response and ultra-low polarization transition barriers in two-dimensional MoGe2N4/MoSi2N4 heterostructures

With the help of the first principle calculations, two-dimensional (2D) MoGe2N4/MoSi2N4 van der Waals (vdW) heterojunction was confirmed as a type II bandgap arrangement with distinct piezoelectric properties dependent on the stacking orders and interlayer interactions. This structural change is facilitated by slip interactions between the layers and is characterized by a process with a low energy barrier, allowing for efficient and responsive phase transition of structures. Notably, this heterojunction exhibits a particularly large out-of-plane piezoelectric coefficient, d33, within a finite thickness. Concurrently, the piezoelectric coefficient can be enhanced by adjusting the vertical strain to a specific value, and the out-of-plane piezoelectric coefficient d33 can be as high as 73.28 pm/V, which is larger than the values of the available 2D materials or their heterojunctions. In addition, we simulated a piezoelectric actuator on a two-dimensional scale, where the deformation of the upper surface of the piezoelectric brake was linearly modulated by adjusting the driving voltage. Thus, our research paves the way for the conceptualization and creation of cutting-edge nanoelectronic devices, electromechanical systems, and multifunctional atomic-scale appliances.

Improving piezoelectric performance in PMN-0.26 PT single crystal via low frequency AC poling

In this experiment, the alternating current poling (ACP) was applied to the 0.74 Pb(Mg1/3Nb2/3)O3-0.26PbTiO3 (PMN-0.26 PT) single crystal to explore the impact of low frequency (0.1 Hz) ACP on electrical performance. When the poling condition is loading 5 cycles at 14 kV/cm, high piezoelectric coefficient d33 of 1780 pC/N and giant dielectric constant of 5881 are obtained for the ACP treatment sample, enhanced 42.4 % and 14.3 % by contrast with the conventional direct current poling (DCP), respectively. The values of coercive field, maximum strain, and converse piezoelectric constant d33∗ vary considerably around the ferroelectric phase transition detected by polarization-electric field, as well as bipolar and unipolar electric field-induced strain hysteresis loops. In addition, the domain configuration of the ACP sample presents a more periodic stripe-like structure with narrower width and relatively more uniformity after three months aging as compared with the DCP sample, showing the importance of domain engineering in enhancing electrical performance of ferroelectric single crystals.

Enhancing piezoelectric coefficient and thermal stability in lead-free piezoceramics: insights at the atomic-scale

Given the highly temperature-sensitive nature of the polymorphic phase boundaries, attaining excellent piezoelectric coefficient with superior temperature stability in lead-free piezoceramics via direct compositional design remains a formidable challenge. We demonstrate the synergistic improvement of piezoelectric coefficient and thermal stability in lead-free piezoceramics via atomic-scale local ferroelectric structure design. Via modulation of the local Landau energy barrier at doping sites, we effectively mitigate fluctuations in piezoelectric d33. Our approach achieves an impressive d33 of ~430 pC/N with a minimal temperature fluctuation range (△d33 ~ 7%) across the room temperature to 100 °C in potassium sodium niobate ceramics. Further optimization through annealing extends this temperature up to 150 °C (△d33 ~ 8%) while maintaining a high d33 of ~380 pC/N, rivaling the performance of classic temperature stable lead zirconate titanate. This work establishes a framework for addressing the dilemma between high piezoelectric coefficient and inadequate temperature stability in lead-free piezoceramics.

Theoretical study of the strong piezo-phototronic effect in 2D monochalcogenides for multi-junction solar cells

The piezophototronic effect is a new scientific area that investigates the synergistic interactions of piezoelectric, semiconductor, and photoexcitation features. This effect is seen in crystals lacking inversion symmetry, where applied strain alters electronic transport and provides a way to modify material properties. Monolayer 2D semiconductors, such as transition metal dichalcogenides (TMDCs) and group IV monochalcogenides, have higher piezoelectric coefficients than conventional piezoelectric materials. This study proposes the development of a stable, high-performance multijunction solar cell (MJSC) leveraging the piezo-phototronic effect. The emphasis is on single-type 5-layer 2D monochalcogenides (SnS, SnSe, GeS, and GeSe) with the assistance of strain engineering. Surprisingly, the ultrathin parallel-connected solar cell achieves an electric power conversion efficiency of over 31% when tested under blackbody radiation, surpassing the recognized Shockley–Queisser (S-Q) limit. The piezophototronic effect improves solar cell performance while also addressing voltage mismatch issues. This work introduces a novel approach to developing and manufacturing high-efficiency and robust monolayer multijunction photovoltaic solar cells (MJPSC) based on 2D monochalcogenides.

On the measurement of piezoelectric d33 coefficient of soft thin films under weak mechanical loads: A rapid and affordable method

Thanks to their intrinsic flexibility, energy efficiency and high portability, soft piezoelectric thin films represent the most effective technological approach for wearable devices to monitor health conditions. In order to improve effectiveness and applicability, more and more innovative and high-performing soft piezoelectric materials are being developed and benchmarked through their piezoelectric d33 coefficient. However, most existing methods to measure the d33 were developed for ceramic or bulk materials and cannot be applied to soft materials because high force/pressure can deform and damage the material structure. This work introduces a simple, effective, and fast method to accurately measure the d33 of soft and thin piezoelectric films by applying weak sinusoidal forces to avoid any damage to the sample, and simultaneously measuring the charges produced by the direct piezoelectric effect. The approach is versatile as it can be used for different types of materials and sizes of the active area. This method represents an effective solution to speed up the process of material optimization, paving the way for the rapid development of novel wearable piezoelectric devices.

Effect of epoxy resin addition on the acoustic impedance, microstructure, dielectric and piezoelectric properties of 1–3 connectivity lead-free barium zirconate titanate ceramic cement-based composites

In this work, 1–3 connectivity barium zirconate titanate ceramic cement-based composites were fabricated using Portland cement and epoxy resin as the matrix. Barium zirconate titanate (BZT) of 40–60 % by volume was used while epoxy was used with cement at 0–7% by volume. Dielectric and piezoelectric properties, and other properties such as acoustic impedance, density and microstructure were investigated. It was found that epoxy resin can be used in combination with BZT to achieve a suitable acoustic impedance value (9–11 × 106 kg/m·s2) matching that of concrete for structural health monitoring application. Thus, when epoxy resin was used at 7 %, BZT volume can be increased to 60 % where the highest d33 value of 93 pC/N was found and remain within the acoustic matching range. In addition, when epoxy resin was increased, both piezoelectric charge coefficient (d33) and piezoelectric voltage coefficient (g33) were also found to increase. This is likely due to the lower porosity thus denser matrix when epoxy resin was used in addition to cement.

Multi-iteration active learning for the composition design of potassium–sodium niobate ceramics with enhanced piezoelectric coefficient

The piezoelectricity of piezoceramics considerably depends on the doped compositions. However, the conventional trial-and-error approach to composition design is time-consuming and inefficient when searching for high-performance piezoceramics with various dopants. In this study, we introduce a data-driven framework to accelerate the design and discovery of lead-free (K,Na)NbO3 (KNN) materials with enhanced piezoelectric performance. The proposed framework integrates machine learning with feature engineering, surrogate-based optimisation, and experimentation in an active learning loop. Using feature engineering techniques, we demonstrated that the piezoelectric coefficient d33 of KNN materials can be predicted based on a set of elemental and atomic properties. We evaluated six machine learning models and found that support vector regression with a radial basis function kernel achieved high accuracy in predicting the d33 values of KNN ceramics. After three iterations of experimentation and optimisation, we identified an optimal composition with a relatively high d33 of ∼353 pC/N from thousands of possible compositions using a pure exploitation strategy. This study demonstrates an efficient and systematic approach to the composition design of KNN-based piezoceramics, which can be applied to investigate the diverse functional properties of other materials.

Analysis and Guideline for Determining Piezoelectric Coefficient for Films With Substrate Constraint.

Piezoelectric films including coatings are widely employed in various electromechanical devices. Precise measurement for piezoelectric film properties is crucial for both piezoelectric material development and design of the piezoelectric devices. However, substrate constraint on the deformation of piezoelectric films could cause significant impacts on the reliability and accuracy of the piezoelectric coefficient measurement. Through both theoretical finite element analysis (FEA) and experimental validation, here we have identified three important factors that strongly affect the measurement results: ratio of Young's modulus of substrate to piezoelectric film, ratio of electrode size to substrate thickness, and test frequency. Our investigations show that a relatively smaller substrate's Young's modulus to film, and a larger ratio of electrode size to substrate thickness would cause a larger substrate bending effect and thus potentially more significant measurement errors. Moreover, intense transversal displacement fluctuation can be excited at excessively high frequencies, leading to unreliable measurements. Various well-established piezoelectric measurement methods are compared with outstanding measurement issues identified for those commonly used piezoelectric films and substrates. We further establish the guidelines for piezoelectric coefficient measurements to achieve high reliability and accuracy, thus important to the wide technical community with interests in electromechanical active materials and devices.

Advancing piezoelectricity and excellent thermal stability: -textured 0.75BF–0.25BT lead-free ceramics for high temperature applications

There is an urgent need for piezoelectric materials possessing both high piezoelectric properties and good thermal stability to facilitate the advancement of high temperature piezoelectric devices. However, conventional strategy for enhancing piezoelectricity via chemical modifications often comes at the cost of thermal stability due to a drop in Curie temperatures. In this study, we achieved remarkable results in <001>-oriented 0.75BiFeO3–0.25BaTiO3 (0.75BF–0.25BT) lead-free textured ceramics. These textured ceramics exhibit a high Curie temperatures Tc of 552 °C, large piezoelectric coefficients d33 of 265 pC/N, and exceptional piezoelectric thermal stability, with minimal variation of 8% across temperature from 25 °C to 300 °C. Compared to randomly oriented ceramics, the piezoelectric coefficient is about 2.5 times higher, marking it as one of the highest reported value for ceramics with Tc near 550 °C. The enhanced piezoelectric properties can be ascribed to improvements in both intrinsic lattice distortions and extrinsic non-180o domain motions, while the excellent piezoelectric thermal stability is attributed to the stable domain texture. These superior properties of the studied textured 0.75BF–0.25BT ceramics position them as competitive lead-free candidates for high-temperature piezoelectric applications.

Density functional theory study on the electronic structures and piezoelectric properties of hydrogenated monolayer II-VI semiconductor XYH2 (X = Zn, Cd; Y = S, Se, Te)

Piezoelectric materials have been widely used in various fields such as sensing and energy catalysis. This paper primarily investigates the structural, electronic and piezoelectric properties of hydrogenated II-VI monolayer semiconductor XYH2 (X = Zn, Cd; Y = S, Se, Te) by density functional theory. Results reveal that XYH2 monolayers exhibit stable hexagonal structures and tunable bandgaps ranging from 3.27 eV to 4.30 eV. Density functional perturbation theory is employed to investigate the out-of-plane piezoelectric coefficients of XYH2 monolayers. CdSH2 exhibits a value of −1.8 pm/V of out-of-plane piezoelectric coefficients which surpasses typical piezoelectric materials such as bulk ZnS (0.076 pm/V), ZnO (0.21 pm/V), CdS (0.143 pm/V), CdSe (0.104 pm/V), BN (0.33 pm/V) and GaN (0.96 pm/V). Our results indicate that hydrogenated II-VI monolayers can be a new type of novel piezoelectric semiconductors and hold a potential application for the piezoelectric devices.

Piezoelectric barium titanate/hydroxyapatite composite coatings on Ti-6Al-4V alloy via electrophoretic deposition

Electrophoretic deposition (EPD) is a widely accepted, cost-effective and simple method to obtain conformal coatings of dense nanoparticles via application of a DC voltage. This paper reports the physical and mechanical properties of nanostructured barium titanate/hydroxyapatite (BT/HA) ceramic composites coated onto Ti-6Al-4V alloy via cathodic EPD in various ratios of 40:60, 50:50 and 60:40 (HB4, HB5 and HB6) respectively. Homogenous BT/HA coatings were obtained at a notably low voltage of 10 V. The crystallinity and phase analysis confirmed the formation of tetragonal phase of BT indicating the piezoelectric property. HB6 exhibits maximum piezoelectric coefficient (d33) of 159 pC/N and Vicker's hardness of 242.31 HV. The cross-sectional electron micrographs show well connected and homogeneous coatings with increasing amounts of BT. Human mesenchymal stem cell lines were utilized in biocompatibility experiments, which revealed that HB composites had greater viability of HW-MSCs cells than pure BT, with HB6 exhibiting a maximum cell viability of more than 90 %.

Structure distortion enhanced electrical performances of Na0.25K0.25Bi2.5Nb2O9-based high-temperature piezoceramics

Na0.25K0.25Bi2.5Nb2O9-based piezoelectric ceramics are potential candidates for high-temperature applications where improving piezoelectric properties is an urgent issue. In this work, significantly improved piezoelectric properties and thermal stability of Na0.25K0.25Bi2.5-xCexNb2-yWyO9 (abbreviated NKB2.5-xCxN2-yWy, x = 0.03, y = 0.01, y = 0.03, y = 0.05) ceramics were obtained through Ce and W co-doping and using a traditional solid-state technique. The optimal composition of NaKBi2.47Ce0.03Nb1.99W0.01O9 exhibits a large piezoelectric coefficient d33 of 23.1 pC/N, maintains a high Curie temperature Tc of 690 °C, and a low tanδ of 0.006. The increase of d33 may be attributed to the structure distortion, the micro-sized domains, and the high-density domain walls. More importantly, its d33 value maintains 86 % of the initial value after being annealed at 650 °C for 2 h, whereas only 65 % for the undoped sample under the same conditions, indicating an obviously improved thermal stability. This work provides a new idea for improving piezoelectric properties and thermal stability of Na0.25K0.25Bi2.5Nb2O9-based piezoelectric ceramics.

Enhanced magnetoelectric response in Sc-doped BiFeO3-BaTiO3 Ceramics

In recent years, the single-phase BiFeO3-BaTiO3 multiferroic ceramics have gained attention for their magnetoelectric response above room temperature, but substantial endeavors to improve the property have yielded modest results. An optimized BiFe(1-x)ScxO3-BaTiO3 composition having magnetoelectric coefficient (αME) ∼ 567 mV/(cm·Oe)) measured at the resonant frequency (∼95 kHz) is reported in this work. The high αME is attributed to the combined effect of improved piezoelectric coefficient and enhanced ferromagnetism. Improved piezoelectricity is attributed to enhanced intrinsic response caused by the octahedral distortions, and enhanced ferromagnetism is induced by the destabilized cycloidal spin structure resulting from the octahedral distortions. Besides, the addition of Sc3+ can exhibit increased resistivity and reduced defect dipole effects, which is conducive to improving electric properties.

Exploring the mechanisms of enhanced piezoelectric properties in (K,Na)NbO3 single crystals

(K,Na)NbO3 (KNN)-based piezoelectric materials are candidates for replacing Pb-based materials. However, the piezoelectric properties of existing KNN-based single crystals are still inferior to those of Pb-based relaxor ferroelectric single crystals. Moreover, the piezoelectric response mechanism of KNN-based single crystals remains unclear. In this study, (Li,K,Na)(Nb,Sb,Ta)O3:Mn (KNNLST:Mn) single crystals with an excellent piezoelectric coefficient d33 of approximately 778 pC/N were prepared. Systematically studies of intrinsic and extrinsic piezoelectric responses have revealed that the high d33 of KNNLST:Mn single crystals is related to the shear piezoelectric response of a single-domain state and irreversible domain wall motion of the engineering domains. Furthermore, the effect of the orthorhombic (O)-tetragonal (T) phase boundary on intrinsic and extrinsic piezoelectric response is systematically studied, and the impact mechanism is elucidated. The results indicate that a lower dielectric response and elastic constant limit the intrinsic shear piezoelectric response of KNNLST:Mn single crystals, and approaching the O–T phase boundary can enhance both intrinsic and extrinsic piezoelectric responses. This study improves our understanding of the structure-performance relationship in KNN-based single crystals and offers insights for optimizing piezoelectric properties in KNN-based materials.

Achieving coaxial photoacoustic/ultrasound dual-modality imaging by high-performance Sm: 0.72PMN-0.28PT transparent piezoelectric ceramic

As a promising new medical imaging method, photoacoustic imaging (PAI) has the advantages of optical resolution and acoustic depth of penetration. The transparent ultrasound transducer (TUT), as a novel device applied to PAI, can combine the laser and acoustic beam coaxially to improve the imaging quality. Transparent piezoelectric materials are the key to developing piezoelectric TUTs. However, due to the birefringence and light scattering caused by ferroelectric domains, it is very hard to prepare transparent piezoelectric materials with both high optical transmittance and excellent piezoelectricity. In this study, 2.5mol% Sm-doped 0.72Pb(Mg1/3Nb2/3)O3-0.28PbTiO3 (PMN-PT) ceramic with a piezoelectric coefficient d33 of 1460 pC N-1 and an optical transmission of 69% at Near-Infrared (NIR) is successfully prepared, and its optical, microstructure, ferroelectric and dielectric properties are fully studied. Subsequently, a 3 mm-diameter photoacoustic coaxial probe is fabricated, involving a transparent ultrasound transducer based on the prepared ceramic. The TUT has a center frequency (fc) of 18.5MHz, a −6dB bandwidth of 20%, and a high effective electromechanical factor (keff) of 0.62. In addition, the imaging capability of the miniature probe is firstly confirmed through PA/US dual-modality imaging of in-vivo animals and phantoms, which indicates that the proposed transparent piezoelectric ceramic has great potential for photoacoustic/ultrasound imaging.

Revealing multiphase coexistence of R-O-T phases in BaTiO3-CaTiO3-BaSnO3 electroceramics for energy harvesting and storage response with piezo actuation

The (Ba1-xCax)(SnyTi1-y)O3 piezoelectric ceramics (where x=0.016, y=0.024; x=0.032, y=0.048; x=0.048, y=0.072; x=0.064, y=0.096; x=0.08, y=0.12) were designed by conventional solid state reaction method. The crystal structure for the composition of x=0.064 and y=0.096 (abbreviated as BCST-4) possesses the coexistence of non-centrosymmetric rhombohedral-orthorhombic-tetragonal (R-O-T) tri-lattice symmetries at room temperature, as demonstrated by the structural Rietveld refinement, Raman analysis, and temperature dependence of dielectric study. Because of the R-O-T multiphase coexistence, BCST-4 possesses a superior electromechanical and piezoelectric property viz. kp ∼ 0.45, strain ∼ 0.100 %, d33* ∼ 649 pm/V, and an improved d33 ∼ 452 pC/N, which is comparable to commercially available soft PZT ceramics (d33 ⁓ 370 pC/N). For BCST-4 ceramics, an exceptional electrostriction coefficient Q33 ∼ 0.0434 m4/C2 value was attained. The intrinsic piezo-actuation DC strain was observed to be 130 microstrain (με) and 188 με with ε33 and ε31 modes respectively. The BCST-4 ceramic exhibits a maximum output power of 1.03 mW, a power density of 13.5 µW/mm3, a maximum output current of 88 µA, and an open circuit voltage Vpp of 28 V which successfully glowed ‘SPPU’ panel having 40 red commercial light-emitting diodes (LEDs). The energy storage study reveals that BCST-4 ceramics exhibit a maximum energy storage density (Wrec) of 165.87 mJ/cm3 with efficiency (ƞ) 68.00 %. Therefore, the improvement in electrostriction coefficient, piezoelectric charge coefficient, and energy storage response indicates that BCST-4 ceramic has the potential for actuator, energy harvesting, and energy storage applications.

A strategy for improving piezoelectricity and thermal stability of Na0.25K0.25Bi2.5Nb2O9-based piezoceramics via A/B-site co-doping

Obviously improved piezoelectricity and thermal stability of Na0.25K0.25Bi2.5Nb2O9-based ceramics have been urgently required for high-temperature piezoelectric applications. In this work, Na0.25K0.25Bi2.5-xCexNb2-yWyO9 (NKBCxNWy, x = 0.01, 0.02, 0.03, 0.04; y = 0.02) piezoceramics were developed via a traditional solid-state reaction method. The effect of Ce/W co-doping on the crystal structure and microscopic morphology was systematically investigated, along with the ferroelectric domains and electrical properties. An optimum composition of Na0.25K0.25Bi2.48Ce0.02Nb1.98W0.02O9 was achieved, which shows a high curie temperature of 670 ℃, a good piezoelectric coefficient d33 of 24.4 pC/N. The enhanced d33 stems from small domain sizes and high domain wall density in NKBC0.02NW0.02 ceramics. More importantly, the maximum d33 can remain above 80 % of the d33 (@25 ℃), even if the annealing temperature increases to 500 ℃. This work provides a simple and viable method to obtain high piezoelectric properties and excellent thermal stability in Na0.25K0.25Bi2.5Nb2O9-based ceramics.

Self-powered highly stretchable ferroelectret nanogenerator towards intelligent sports

Ferroelectret nanogenerators (FENGs), recognized for their porous structures that facilitate charge retention, thereby creating giant electric dipoles and exhibiting remarkable piezoelectric properties, are utilized in the development of various flexible transducers. However, despite their flexibility, most developed ferroelectret nanogenerators lack adequate stretchability and satisfactory transverse piezoelectric properties, significantly inhibiting their widespread deployment in wearable or skin-mounted electronics. Here, we introduce a highly stretchable ferroelectret nanogenerator (HS-FENG) built from laser-induced graphene (LIG), Ecoflex and anhydrous ethanol, demonstrating exceptional flexibility and stretchability, along with longitudinal and transverse piezoelectric effects. The stretchability of HS-FENG can reach a record of 468 %, while the quasi-static piezoelectric coefficients d33 and d31 are approximately 120 pC/N and 70 pC/N, respectively. To our knowledge, this is the first demonstration of the developed FENG with remarkably high stretchability. Furthermore, leveraging the performance of the created HS-FENG, we construct a skin-mounted intelligent kinesiology tape capable of effectively monitoring motion signals from human muscles and joints, thereby offering a deeper understanding of movement for users across different levels of physical activity, from professional athletes to individuals undergoing rehabilitation. The development of intelligent kinesiology tape exemplifies the potential of HS-FENG technology in enhancing professional athletic training and personalized healthcare. It contributes to the advancement of inconspicuous skin-mounted biomechanical feedback systems and human-machine interfaces, marking progress in the field.

Effect of compressive stress on piezoelectric coefficients: A multiscale modeling approach

The effect of compressive stress on linearized coefficients for ferroelectric ceramics has been extensively reported experimentally. However, there is no proper model for this effect which could be pertinent to designers of force sensors. This paper introduces a model based on a ferroelectric multiscale model in order to predict the effect of compressive stress on the piezoelectric constitutive laws. The comparison with experimental data shows an excellent qualitative agreement and the use of this model gives new insights on this nonlinear and hysteretic effect.