Piezoelectric Coefficient D33 Research Articles

Compressive stress reduction in sputter-deposited yttrium aluminum nitride (Y0.2Al0.8N) thin films for BAW resonators with high electromechanical coupling

In the past decade, rare earth elements have found increasing interest in enhancing the piezoelectric coefficient of aluminum nitride (AlN) thin films. Until now, scandium has been the most successful rare earth element to enhance the piezoelectric coefficient (d33) up to 600 %. In this research paper, we present a 250 % increase in d33 to 12.5 pC/N for sputter-deposited yttrium alloyed aluminum nitride (Y0.2Al0.8N) thin films compared to pure AlN. However, this increase in d33 comes with a substantial increase in compressive layer stress well above 1 GPa. Therefore, a chamber pressure sweep technique is introduced, resulting in a 40 % reduction in the stress level without significantly affecting the crystallographic film parameters to facilitate device integration. Even more, high compressive stress in thin films is a critical concern in piezoelectric MEMS devices such as bulk acoustic wave (BAW) resonators, as it can adversely affect the piezoelectric material properties and hence, the electromechanical performance. For this purpose, we demonstrate that the pressure sweep technique improves the electromechanical coupling factor of Y0.2Al0.8N to 7.02 %, being substantially above the reference value of 6.02 % set by pure AlN. In summary, the findings from this study may stimulate further effort to integrate YxAl1-xN thin films in BAW filter devices for future telecommunication applications.

Adaptive ferroelectric states in KNN-based piezoceramics: Unveiling the mechanism of enhancing piezoelectric properties through multiple phase boundary engineering

Developing high-performance lead-free piezoceramics, such as (K,Na)NbO3 (KNN) material, is critical to achieving environmental sustainability in next-generation electromechanical devices. Although substantial advancements have been made in KNN-based ceramics, a general coherent framework is lacking that links microscopic structure to the enhancement of macroscopic properties. Our findings indicate that the enhanced performance of KNN-based ceramics in multiphase coexistence boundaries can be attributed to the formation of self-adjusting nanodomains in response to strong local structural heterogeneity. The self-adjusting behavior of domain structure is an outcome of minimizing the local stress generated by the lattice mismatch within KNN-based ceramics, which conforms to the thermodynamic principles that favor minimizing total free energy. Guided by this strategy, the present work achieves a significant improvement of electromechanical properties, including a piezoelectric coefficient (d33) of ∼585 pC N−1, an electromechanical coupling factor (kp) of ∼62 %, and a figure of merit (d33 × g33) of ∼12.78 ×10−12 m2 N−1. This study offers a new strategy for developing lead-free piezoceramics through dedicated design of novel phase boundaries.

Restraining quenching-induced decline of resistivity in NBT-BFO ceramics by incorporation of BiAlO3

(1-x)Na0.5Bi0.5TiO3-xBiFeO3 (NBT-BFO) is a system with a composition-induced transition from relaxor to ferroelectric. Upon quenching, 0.4NBT-0.6BFO obtain a Td of 640 °C and d33 of 56 pC/N. However, the quenching treatment also causes the reduction of resistivity, which is unfavorable for high-temperature piezoelectric ceramics. The aim of this study is to restrain quenching-induced decline of resistance in NBT-BFO ceramics by doping a small amount of BiAlO3 (BA). For unquenched NBT-BFO-BA, with increasing BA content, the piezoelectric coefficient (d33) decreases slightly, while the resistivity increases. After quenching, both d33 and the depolarization temperature (Td) increase, but more importantly, the resistivity of quenched NBT-BFO-BA is comparable with that of the unquenched samples. This phenomenon is not observed in other quenched samples, and the reason is attributed to the defect dipoles caused by BA. Besides, the enhanced piezoelectric properties and the resistivity can be retained after annealing the quenched samples at 400 °C for 4 h. Thus, this work implies the potential application of NBT-BFO based piezoelectric ceramics at elevated temperatures.

Giant field-induced strain with excellent fatigue performance in (Al0.5Nb0.5)4+-modified 0.85Bi0.5Na0.5TiO3-0.11Bi0.5K0.5TiO3-0.04BaTiO3 piezoelectric ceramics

Utilizing a conventional solid-state reaction procedure, (Al0.5Nb0.5)4+-modified 0.85Bi0.5Na0.5TiO3-0.11Bi0.5K0.5TiO3-0.04BaTiO3 (BNKT-BT) samples were synthesized. The impact of (Al0.5Nb0.5)4+ on the crystal structure, ferroelectric, dielectric, and AC impedance properties was systematically investigated. The XRD patterns demonstrate that the crystal structures of all samples exhibit typical pseudo-cubic features. According to the XPS, the doping of (Al0.5Nb0.5)4+ reduces the concentration of oxygen vacancies inside the ceramics, which significantly affects the relaxation properties. This substitution successfully triggers a change from a non-ergodic relaxor (NR) state to an ergodic relaxor (ER) state, which is ascribed to the weakening of the pinning effect of the oxygen vacancies on the polar nanoregions (PNRs). The ceramics exhibit an enormous monopolar strain of 0.468% under 60kV/cm, accompanied by an inverse piezoelectric coefficient (d33⁎) of 780pm/V, surpassing the performance of numerous other BNT-based piezoelectric ceramics. After 1×104 switching cycles, the strain value changes slightly, indicating excellent fatigue performance. The considerable strain arises from a reversible transformation of the ER phase to the ferroelectric phase induced by an electric field. This research suggests that (Al0.5Nb0.5)4+-doped BNKT-BT ceramics have good prospects for application in actuators and sensors.

Narrow-Bandgap Tellurium-Based Chiral Hybrid Perovskite Single Crystals with Rashba-Dresselhaus Effect and Piezoelectricity.

Chiral hybrid perovskites have aroused great interest due to their unique versatile properties. However, designing chiral perovskites with narrow bandgaps is challenging, with their electronic properties such as the Rashba-Dresselhaus effect and piezoelectricity remaining unclear. Herein, single crystals of zero-dimensional (0D) tellurium-based chiral hybrid perovskite, (R-/S-α-PEA)2TeI6 and (R-/S-α-PEA)2TeBr6 (PEA = phenylethylammonium), with sizes of over 5 mm are grown by seed-crystal-assisted solution-temperature-lowering. The optical bandgaps are about 1.60 and 2.18 eV for the iodide and bromide analogues, respectively, which are the lowest among various chiral lead-free hybrid perovskites with the same halide ions in the X-site to the best of our knowledge. First-principles calculations reveal that (R-/S-α-PEA)2TeBr6 shows a larger Rashba-Dresselhaus spin-splitting than (R-/S-α-PEA)2TeI6, probably thanks to the greater distortion of [TeBr6] octahedra. Moreover, the piezoelectric coefficients d33 of (R-/S-α-PEA)2TeI6 and (R-/S-α-PEA)2TeBr6 are about 2.6 and 1.8 pC N-1, respectively. This work deepens the understanding of physical properties of 0D tellurium-based chiral perovskites with potential multifunctionality, including spintronic and piezoelectric performances.

Ultra-high electrostrain in flux-grown (Bi0.5Na0.5)TiO3-0.06BaTiO3-0.03(K0.5Na0.5)NbO3 single crystals around the nonergodic/ergodic crossover region

In this study, we successfully grew large-sized single crystals (12 × 11 × 8 mm³) of 0.91Bi0.5Na0.5TiO3-0.06BaTiO3-0.03(K0.5Na0.5)NbO3 (BNT-6BT-3KNN) with a <100>c orientation using the flux growth method. This marks the first instance of achieving such crystals. The single crystals display double hysteresis loops, featuring a maximum polarization of ∼64.6 μC/cm2. Capitalizing on the nonergodic/ergodic boundary, the single crystals exhibit a substantial strain (Sm) of 0.91% at the maximum electric field of 20 kV/cm and an exceptionally high inverse piezoelectric coefficient d33* of 4550 pm/V. The creation of long-range domains from needle-like nanodomains and polar-nano regions under the application of an electric field was confirmed through bright-field transmission electron microscopy and piezoresponse force microscopy analyses. The phase diagram for BNT-6BT-3KNN single crystals was constructed by analyzing the temperature dependence of dielectric, ferroelectric, and electrostrain behaviors.

Recent Advances in Ferroelectret Fabrication, Performance Optimization, and Applications.

The growing demand for wearable devices has sparked a significant interest in ferroelectret films. They possess flexibility and exceptional piezoelectric properties due to strong macroscopic dipoles formed by charges trapped at the interface of their internal cavities. This review of ferroelectrets focuses on the latest progress in fabrication techniques for high temperature resistant ferroelectrets with regular and engineered cavities, strategies for optimizing their piezoelectric performance, and novel applications. The charging mechanisms of bipolar and unipolar ferroelectrets with closed and open-cavity structures are explained first. Next, the preparation and piezoelectric behavior of ferroelectret films with closed, open, and regular cavity structures using various materials are discussed. Three widely used models for predicting the piezoelectric coefficients (d33) are outlined. Methods for enhancing the piezoelectric performance such as optimized cavity design, utilization of fabric electrodes, injection of additional ions, application of DC bias voltage, and synergy of foam structure and ferroelectric effect are illustrated. A variety of applications of ferroelectret films in acoustic devices, wearable monitors, pressure sensors, and energy harvesters are presented. Finally, the future development trends of ferroelectrets toward fabrication and performance optimization are summarized along with its potential for integration with intelligent systems and large-scale preparation.

Challenges and opportunities in piezoelectric polymers: Effect of oriented amorphous fraction in ferroelectric semicrystalline polymers

AbstractDespite extensive research on piezoelectric polymers since the discovery of piezoelectric poly(vinylidene fluoride) (PVDF) in 1969, the fundamental physics of polymer piezoelectricity has remained elusive. Based on the classic principle of piezoelectricity, polymer piezoelectricity should originate from the polar crystalline phase. Surprisingly, the crystal contribution to the piezoelectric strain coefficient d31 is determined to be less than 10%, primarily owing to the difficulty in changing the molecular bond lengths and bond angles. Instead, &gt;85% contribution is from Poisson's ratio, which is closely related to the oriented amorphous fraction (OAF) in uniaxially stretched films of semicrystalline ferroelectric (FE) polymers. In this perspective, the semicrystalline structure–piezoelectric property relationship is revealed using PVDF‐based FE polymers as a model system. In melt‐processed FE polymers, the OAF is often present and links the crystalline lamellae to the isotropic amorphous fraction. Molecular dynamics simulations demonstrate that the electrostrictive conformation transformation of the OAF chains induces a polarization change upon the application of either a stress (the direct piezoelectric effect) or an electric field (the converse piezoelectric effect). Meanwhile, relaxor‐like secondary crystals in OAF (SCOAF), which are favored to grow in the extended‐chain crystal (ECC) structure, can further enhance the piezoelectricity. However, the ECC structure is difficult to achieve in PVDF homopolymers without high‐pressure crystallization. We have discovered that high‐power ultrasonication can effectively induce SCOAF in PVDF homopolymers to improve its piezoelectric performance. Finally, we envision that the electrostrictive OAF mechanism should also be applicable for other FE polymers such as odd‐numbered nylons and piezoelectric biopolymers.

Piezoelectric, magnetic and magnetoelectric properties of the flexible layered Ni/PVDF-TrFE/Ni structures

A study of the magnetoelectric properties of layered structures based on polyvinylidene fluoride trifluoroethylene (PVDF-TrFE) and nickel films of various thicknesses is presented.The value of the piezoelectric coefficient d33 for prepolarized samples was ∼33pC/N. The maximum value of the magnetoelectric coefficient of 110 mV/A is observed for structures with a nickel coating with a thickness of hNi = 40 μm on each side. It has been established that the piezoelectric coefficient decreases with increasing nickel coating thickness from 24pC/N structures with hNi = 10 μm to 18pC/N at hNi = 40 μm. The specific magnetostriction of nickel coatings changes insignificantly with changes in the film thickness. The increase in the ME coefficient is due to the joint contribution from the decreasing piezoelectric modulus and the increasing magnetostriction of the composite. The resulting layered heterostructures retain flexibility and have a high linear ME coefficient in the low-frequency region, which makes it possible to use such materials in the development of flexible energy harvesters.

Giant strain and excellent anti-fatigue properties of La3+ doped (Na0.84K0.16)0.5Bi0.5Ti0.985Ta0.015O3 lead-free ceramics

Lead-free piezoelectric ceramics [(Na0.84K0.16)0.5Bi0.5]1-xLaxTi0.985Ta0.015O3 (BNKTT-100xLa) were synthesized by traditional solid phase reaction. The influences of La3+ doping on ceramic materials’ microstructure, ferroelectric, and dielectric properties were investigated systematically. XRD patterns indicated that La3+ fully diffuse into the BNKTT lattice and form a single solid solution. SEM images showed that the surface of all samples was compact and no heterophase appeared. The ferroelectric-relaxor phase transition temperature gradually moved to low temperature with the increase of La3+ doping, which was beneficial to obtain large electro-strain. The maximum unipolar strain of BNKTT-1La ceramics can reach ∼0.439 % at 60 kV/cm corresponding to the inverse piezoelectric coefficient d33∗ of ∼731 pm/V. The strain performance increased significantly to ∼0.895 % at high temperature because the ferroelectric-relaxor phase transition became easier. The BNKTT-1La ceramics showed excellent fatigue resistance after 105 cycles at 60 kV/cm. All these indicated that BNKTT-100xLa ceramics have great application prospects in piezoelectric brakes, strain sensors, and actuators.

A high performance nanocellulose-PVDF based piezoelectric nanogenerator based on the highly active CNF@ZnO via electrospinning technology

Piezoelectric polymer composites have attracted much attention due to their high piezoelectric properties and excellent flexibility. In this work, cellulose nanofiber (CNF) was loaded with ZnO by an improved two-step hydrothermal method to obtain CNF@ZnO composites, which have the advantage at high-efficiency one-step film formation and displays considerable piezoelectric performance. Under the optimized hydrothermal conditions, ZnO can be uniformly loaded on CNF sbstrate. The piezoelectric response of CNF at scattered state and micro-nano scale has been successfully characterized to be 5.85 pm·V−1 via piezoelectric force microscopy (PFM), which can be increased to 9.49 pm·V−1 after loaded with ZnO. The obtained CNF@ZnO was dispersed in polyvinylidene fluoride (PVDF) to prepare a large-format tough PVDF/CNF@ZnO composite membrane (E-PVDF/CZ) by electrospinning. CNF@ZnO can effectively increase β phase in PVDF to be 87.36%, and its piezoelectric response was further enhanced to be 24.65 pm·V−1, along with longitudinal piezoelectric coefficient (d33) of 31±2.07 pC·N−1 higher than that of E-PVDF (20.25±2.05 pC·N−1). It also exhibits excellent mechanical performance and flexibility with the tensile strengthen of 16.12±2.35 MPa and elongation at break of 16.21±2.17%. Under the force of 45 N, the open-circuit voltage (VOC) and short-circuit current (ISC) of E-PVDF/CZ are as high as 11.8 V and 452 nA, respectively. Finally, the prepared flexible sensor has an VOC up to 31.2 V under the fist hitting state, while it is about 1.68 V stimulated by water droplets which can also weakly light a LED. The strategy will exactly facilitate the cellulose material in the application in energy harvesting and environmental monitoring.

Large electrostrain achieved in BNKT‐based ceramics by the adjustment of phase boundary with Ba(Sn0.70Nb0.24)O3 addition

AbstractIn the current study, the incorporation of Ba(Sn0.70Nb0.24)O3 (BSN) effectively modifies the phase boundary of the 0.8(Bi0.50Na0.50)TiO3‐0.2(Bi0.50K0.50)TiO3 (BNKT) lead‐free ceramic material, inducing enhanced electrostrain properties at room temperature, particularly results in a “bud‐like” strain profile without negative strain. A comprehensive investigation has been conducted into the microstructure, electrical properties, and electrostrain properties of the above‐mentioned ceramics. The addition of BSN was observed to be well incorporated into the BNKT crystal structure, forming a single perovskite structure according to the X‐ray diffraction pattern. With the increase in BSN solid solution content, the temperature at which the transition from ferroelectric to the relaxor phase occurs shifted from 88.1°C to beneath room temperature (30°C). Specifically, the BNKT‐0.0075BSN ceramic demonstrated a positive strain response of 0.459% along with a large signal piezoelectric coefficient (d33*) of 643 pm/V. Additionally, the strain hysteresis of the BNKT‐0.0175BSN ceramics was only about 3% at 120°C. These experimental findings suggest that BNKT‐xBSN ceramics could be strong contenders for actuators and sensors, presenting promising opportunities for lead‐free ceramic actuator applications.

Enhanced energy density in piezoelectric PVDF-polymer nanocomposite via multiple mechanism synergetic action

Piezoelectric poly(vinylidene fluoride) (PVDF) polymer exhibits the flexible characteristic, however, a piezo-generator based on the PVDF polymer normally shows low power density because of its low piezoelectric coefficient. Here, we report a fundamental synergistic strategy to prepare PVDF polymer nanocomposite for enhancing electromechanical coupling performance and improving its energy density, including (i) the mechanically directional stress field (MDSF) fabrication of PVDF nanocomposite doped with polar Pb(Zr,Ti)O3 (PZT) ceramic nanoparticles via high-energy ball milling, (ii) introduction of micro-cavities holding polar nanoparticles, and (iii) floating electrode (Ag) films spaced uniformly inside the polymer nanocomposite. The investigations reveal that the MDSF fabrication can induce ordered, chain-shape nanocrystalline fibers with a high β-crystal phase, which makes 42% contribution to the piezoelectricity; while the micro-cavities and floating electrode films after poling exhibit a strong electret effect, which further make 18% and 27% contributions, respectively, to the piezoelectricity. This multiple-mechanism synergistic effect results in a much higher piezoelectric coefficient d33 increased from 4 pC N−1 for a pure PVDF (without bearing a uniaxial stretching) to 33 pC N−1 for the nanocomposite. It further dramatically increases to 228 pC N−1, a giant apparent piezoelectric charge coefficient d33*, for a 3D-printed 7-layer nanocomposite with 360 μm in thickness. An energy harvester (EH) based on the PVDF nanocomposite generates a record high peak power density of 13.2 mW cm−2 and the load power density of 5.46 mW cm−2 under a dynamic pressure of 255 kPa at the frequency of 5 Hz, which is near two orders of magnitude higher than that of a conventional PVDF polymer EHs. The fabricated flexible EH can even directly light up 46 LEDs in real-time or power a blind-man reading system when touching it. This work is of great significance in enlightening future flexible piezoelectronic designs.

Experimental and theoretical investigation on the SR method grown semi-organic Piperazinium Tetrachlorozincate Monohydrate (PTZM) single crystal for optoelectronic applications

Efficient semi organic nonlinear optical (NLO) Piperazinium Tetrachlorozincate monohydrate (PTZM) [C4H12N2][ZnCL4]·H2O single crystals have been grown by slow evaporation solution technique (SEST) and Sankaranarayanan-Ramasamy (SR) method using water as solvent. Single crystal X-ray diffraction (SXRD) analysis reveals the unit cell parameters of the grown crystal. The morphology of the grown crystal was identified by the single crystal XRD analysis. The electrical properties, dielectric constant, dielectric loss and piezoelectric (d33) coefficient were determined. The etch pit density of PTZM crystal has been calculated by using the chemical etching analysis. The laser damage threshold (LDT) analysis was investigated by Nd: YAG laser and the wavelength of laser is 1064 nm. The mechanical stability of the grown PTZM crystal was studied using Vickers microhardness measurement. Utilizing quantum chemical calculations, the PTZM compound is analyzed for vibrational properties, HOMO and LUMO characteristics, NBO interactions, and the determination of first-order hyperpolarizability. The nonlinear susceptibility and first-order hyperpolarizability results provide compelling evidence and affirm the PTZM molecule’s potential as a strong candidate for nonlinear optical (NLO) applications.

Piezoelectric Yield of Single Electrospun Poly(acrylonitrile) Ultrafine Fibers Studied by Piezoresponse Force Microscopy and Numerical Simulations.

Quantitative converse piezoelectric coefficient (d33) mapping of polymer ultrafine fibers of poly(acrylonitrile) (PAN), as well as of poly(vinylidene fluoride) (PVDF) as a reference material, obtained by rotating electrospinning, was carried out by piezoresponse force microscopy in the constant-excitation frequency-modulation mode (CE-FM-PFM). PFM mapping of single fibers reveals their piezoelectric activity and provides information on its distribution along the fiber length. Uniform behavior is typically observed on a length scale of a few micrometers. In some cases, variations with sinusoidal dependence along the fiber are reported, compatibly with a possible twisting around the fiber axis. The observed features of the piezoelectric yield have motivated numerical simulations of the surface displacement in a piezoelectric ultrafine fiber concerned by the electric field generated by biasing of the PFM probe. Uniform alignment of the piezoelectric axis along the fiber would comply with the uniform but strongly variable values observed, and sinusoidal variations were occasionally found on the fibers laying on the conductive substrate. Furthermore, in the latter case, numerical simulations show that the piezoelectric tensor's shear terms should be carefully considered in estimations since they may provide a remarkably different contribution to the overall deformation profile.

Application of multi-layered composite fiber films with enhanced piezoelectric performance in flexible energy harvesting devices

Flexible electronic components such as wearable sensors, energy harvesting devices, and human health monitoring systems based on piezoelectric materials have garnered significant attention within the scientific community. In this study, PZT nanofibers were modified with dopamine hydrochloride prior to their integration into PVDF fibers, serving as piezoelectric reinforcements to enhance the mechanical and piezoelectric characteristics of composite fiber films. Subsequently, a facile hot-pressing method was employed to fabricate multilayered films characterized by a densely packed surface fiber arrangement and a loosely organized internal fiber orientation, which markedly improved the self-supporting ability and fiber density of the electrospun fiber films. A detailed investigation into the micro-morphology, crystallinity, and enhanced piezoelectric properties of the films was conducted. Notably, the composite fiber film containing 6 wt% PZT NFs exhibited a peak piezoelectric coefficient (d33) of 29 pC/N, resulting in an output voltage of 13.8 V. This represents a 2.23-fold enhancement in d33 value and a 4.6-fold increase in output voltage when compared to the pristine PVDF fiber film, which had a d33 of 13 pC/N and an output voltage of 3 V. The power density achieved by the sensor is 0.73 μW/cm2. This performance is underpinned by a high piezoelectric coefficient, outstanding output characteristics, and robust stability, which collectively enhance the sensor's efficacy in various applications. This research presents an effective approach for augmenting the piezoelectric performance of PVDF-based composite films and paves the way for the advancement of piezoelectric energy harvesting applications.

LiNbO3-induced phase structure evolution and improved piezoelectric properties in BiFeO3–BaTiO3 ceramics

Eco-friendly (0.73-x)Bi1.05FeO3-xLiNbO3-0.27BaTiO3 ternary ceramics were designed and prepared via a solid-state sintering route. Based on the X-ray diffraction results and Rietveld refinement, it was found that the structure of the ceramics transformed from rhombohedral to tetragonal symmetry with the addition of LiNbO3, and at x = 0.003, there existed a morphotropic phase boundary separating the two phases. Near the phase boundary, the largest values were achieved for the piezoelectric constant d33 and planar electromechanical coupling coefficient kp, being 180 pC/N and 0.27, respectively. Due to the addition of LiNbO3, the grain size tended to become smaller. Additionally, the ceramics were transitioned from normal to relaxor ferroelectrics with increasing x. Despite the fact that the LiNbO3 addition would result in a gradual decrease of Curie temperature, a relatively high Curie temperature (535 °C) was still maintained at x = 0.003, the phase boundary composition, which also showed good temperature stability of piezoelectric properties. These experimental results can provide a reference for the practical applications of high-temperature lead-free ceramics.

Re-usable Cd0.9Zn0.1S-ZnO@C/PVDF piezo-photocatalytic film with exceptional hydrogen evolution capability triggered by the synergetic advantages of piezoelectricity and S-Scheme heterojunction

Piezoelectric materials have advantages of fine-tuning photocatalytic performance through harvesting mechanical energy and open a new avenue in facilitating green catalytic reaction. Herein, polyvinylidene fluoride (PVDF), a flexible piezoelectric material, was introduced to synthesize a novel Cd0.9Zn0.1S-ZnO@C/PVDF (CZS-ZO@C/PVDF) piezo-photocatalytic film by spin coating and immersion phase conversion method. Benefiting from the piezoelectricity of PVDF and the internal electric field (IEF) of CZS-ZO@C Step-scheme (S-Scheme) heterojunction, CZS-ZO@C/PVDF was able to induce a hydrogen generation rate of 34.9 mmol g−1 h−1 activated by ultrasound and visible light (U-L), which is ∼17.5 times of Cd0.9Zn0.1S/PVDF (CZS/PVDF) and ∼7.4 times of the photocatalysis rate activated by visible light only (L). Piezoelectric measurements and COMSOL simulation illustrated the excellent piezoelectricity of CZS-ZO@C/PVDF film, which exhibits a piezoelectric coefficient (d33) of 9.9 pm V−1 and a piezoelectric potential of 874 mV (under 0.5 MPa). The reaction mechanism for the exceptional piezo-photocatalytic performance was finally disclosed through density functional theory (DFT) calculation and electrochemical tests. This study enriches the application scope of piezoelectric materials in sustainable energy catalysis and provides a new direction to develop efficient piezoelectric photocatalysts.

Ultra-high strain in Bi0.5(Na0.41K0.09)TiO3 Pb-free piezoelectric ceramics modified by Sr(Hf0.5Sb0.4)O3

The lead-free piezoelectric ceramics used in piezoelectric actuators have attracted extensive attention owing to their substantial electric-field-induced strain. In this study, The (1-x)Bi0.5(Na0.41K0.09)TiO3-xSr(Hf0.5Sb0.4)O3 (BNKT-xSHS) piezoelectric ceramics were synthesized using the conventional solid-state reaction method. The impact of SHS substitution on the microstructure and electrical properties was systematically explored. Among them, the BNKT-0.015SHS sample, featuring ergodic relaxor states, demonstrates a high piezoelectric strain coefficient (d33*) of 785 p.m./V under a low electric field of 50 kV/cm(Strain = 0.392 %). It exhibits a repeatable strain value of 0.47 % under an 80 kV/cm electric field(d33* = 590 p.m./V). Moreover, the strain values remain around 0.4 % between room temperature and 100 °C, with variations within 90 %. The heightened repeatable strain response is considered to be linked to the electric field-induced reversible phase transition occurring within the ergodic relaxor state. The higher strain temperature stability is ascribed to the coexistence of quadrilateral polar nanoregions and rhombic polydomain nanoregions. This study provides an effective example for achieving significant strain responses, presenting a feasible candidate material for applications in piezoelectric actuators.

Enhancement of piezoelectric properties of CaBi2Nb2O9 ceramics by Ce doping and direct reaction sintering

CaBi2Nb2O9 (CBN) with the Aurivillius phase has a high Curie temperature (TC) and remarkable fatigue resistance, which has great potential for application as high-temperature sensors. However, due to its low piezoelectric properties, its practical application remains a great challenge. In this paper, Ca1-xCexBi2Nb2O9 ceramics were prepared by the direct reaction sintering (DRS) and conventional preparation (CP) methods, respectively. The experimental results indicate that Ce doping can increase the piezoelectric coefficient d33 of CBN ceramics by about two times. Among them, the grain size of the samples prepared by the DRS method is finer and more uniform, and the d33 value of DRS samples is about 3.6–9.4 % higher than that of CP samples. The DRS sample Ca0·97Ce0·03Bi2Nb2O9 has a d33 value of 18.9 pC/N, a TC of 948 °C, and a resistivity of 1.1 × 105 Ω cm at 600 °C. This study shows that DRS method is an effective densification method, which can prepare CBN-based ceramics with excellent comprehensive properties, and provides an innovative preparation route to explore CBN-based ceramics with excellent piezoelectric properties.