Lead-free Piezoelectric Materials Research Articles

Evaluating the efficacy of lead-free piezoelectric materials in microcantilever based vibration energy harvesters

Abstract The piezoelectric materials have been extensively utilized in various applications, such as sensors, actuators, and energy harvesters. This study evaluates the performance of six lead-free piezoelectric materials- aluminium nitride (AlN), barium titanate (BaTiO3), lithium niobate (LiNbO3), lithium tantalate (LiTaO3), polyvinylidene fluoride (PVDF), and zinc oxide (ZnO) in MEMS-based piezoelectric vibration energy harvesters (PVEHs) using cantilever configurations. Finite element analysis via COMSOL Multiphysics was employed to assess the deflection, voltage, and power outputs of these materials at their resonance frequencies, both with and without proof masses. The results indicate that BaTiO3 and PVDF cantilevers exhibited the highest voltage outputs, reaching 207.14 mV and 202.07 mV, respectively, with AlN also showing comparable performance at 184.72 mV. ZnO-based cantilevers demonstrated the highest power output of 1.35 nW without proof masses and 190.5 nW with proof masses, indicating its potential for high-power applications. The addition of proof masses generally reduced resonant frequencies but enhanced power outputs, like for ZnO. This comprehensive analysis underscores the critical impact of material selection and structural modifications on the efficiency of PVEHs, with BaTiO3, PVDF, and ZnO emerging as the most promising candidates for optimizing energy harvesting devices. This research lays a foundation for further advancements in piezoelectric MEMS technology, aiming for more efficient energy harvesting solutions.

Unlocking Electrostrain in Plastically Deformed Barium Titanate.

Achieving substantial electrostrain alongside a large effective piezoelectric strain coefficient (d33*) in piezoelectric materials remains a formidable challenge for advanced actuator applications. Here, a straightforward approach to enhance these properties by strategically designing the domain structure and controlling the domain switching through the introduction of arrays of ordered {100}<100> dislocations is proposed. This dislocation engineering yields an intrinsic lock-in steady-state electrostrain of 0.69% at a low field of 10kVcm-1 without external stress and an output strain energy density of 5.24Jcm-3 in single-crystal BaTiO3, outperforming the benchmark piezoceramics and relaxor ferroelectric single-crystals. Additionally, applying a compression stress of 6MPa fully unlocks electrostrains exceeding 1%, yielding a remarkable d33* value over 10000pmV-1 and achieving a record-high strain energy density of 11.67Jcm-3. Optical and transmission electron microscopy, paired with laboratory and synchrotron X-ray diffraction, is employed to rationalize the observed electrostrain. Phase-field simulations further elucidate the impact of charged dislocations on domain nucleation and domain switching. These findings present an effective and sustainable strategy for developing high-performance, lead-free piezoelectric materials without the need for additional chemical elements, offering immense potential for actuator technologies.

Boosting Low-E electro-strain via high-electronegativity B-site substitution in lead-free K0.5Na0.5NbO3-based ceramics

Lead-free piezoelectric actuators emerge as promising substitutes for their lead-containing counterparts to address environmental concerns. However, they often confront a trade-off between low driving electric fields and high electro-strain. Herein, a novel strategy to boost electro-strain under low electric fields is proposed by doping high-electronegativity B-site atoms into perovskite potassium sodium niobate-based ceramics. Our findings reveal that high-electronegativity B-site atoms elevate the covalency of B-O bonding, softening the short-range repulsion and introducing local multiphase coexistence. This leads to more nanoscale domain structures and lower coercive field, thereby enabling large strains to be produced at lower electric fields. Notably, a substantial 0.2 % bipolar electro-strain and 0.1 % unipolar electro-strain under 10 kV cm-1 is achieved in Sr, Sb co-doped potassium sodium niobate ceramics, with a broad working frequency and temperature range, as well as excellent fatigue resistance. This study unveils innovative insights into designing lead-free piezoelectric ceramics with remarkable electro-strain performance and low driving electric field, promising a significant advancement in lead-free piezoelectric materials science and piezoelectric actuators.

Fracture behaviors and crack propagation anisotropy in multi-ions modified bismuth titanate ferroelectrics

Bismuth titanate (BIT) is widely considered a promising lead-free piezoelectric material for advanced high-temperature applications. Despite significant advances in high-performance BIT ferroelectrics, there remains little understanding of mechanical properties including fracture failure and crack propagation behaviors, hindering the optimization of stability and reliability for next-generation high-temperature ferroelectrics. In this work, we investigated mechanical fracture and crack propagation behaviors of a type of high-performance bismuth titanate-based ceramic (Bi3.96Ce0.04Ti3–2xWxNbxO12, BCTWN) with different doping contents and electric poling states. High-resolution transmission electron microscopy (HRTEM) and electron backscatter diffraction (EBSD) results reveal that the BCTWN ceramics possess a single ferroelectric phase and exhibit layered crystal structures characterized by periodic fringe features. In addition, the striped domain structures are observed on the surface of plate-like grains. Mechanical measurements indicate that fracture behaviors of BCTWN ceramics are significantly affected by doping contents. The ceramics with the largest grain size present inferior microstructure with more defects, endowing the lowest bending strength and fracture toughness. For the samples with different poling states, strong anisotropy in crack propagation and fracture toughness is observed, attributed to the different domain switching mechanisms driven by local incompatible stress fields, which is experimentally validated by the intriguing evolutions of striped domain structures around crack tips. This work advances our understanding of the fracture and crack propagation mechanisms of BIT-based ceramics and provides insight into tailoring the mechanical behaviors through doping and poling strategies.

Synergistic enhancement of electrical characteristics in Sr2+ and Zr4+ Co-doped BaTiO3 ceramics through multiphase coexistence regulation at room temperature

BaTiO3 (BT)-based ceramics have recently become one of the most promising lead-free piezoelectric ceramics. However, its overall performance still falls short of meeting the demands for multifunctional applications. Although phase boundary regulation can enhance the piezoelectric properties, BT ceramics have very separate phase transition temperatures for different phases. This leads to the difficulty of achieving multiphase coexistence at room temperature (RT). In this work, based on doping 0.08 mol Zr4+, the lead-free Ba1-xSrxTi0.92Zr0.08O3 [x = 0, 0.04, 0.08, 0.12, 0.16, 0.20 (mol), B1-xSxTZ] piezoelectric ceramics were prepared using the solid-state reaction method, and the effect of the Sr2+ doping level on the multiphase structural evolution and piezoelectric properties was systematically investigated. The results demonstrated that with the increase in the Sr2+ doping content, multiphase coexistence within the B1-xSxTZ ceramics was successfully achieved at RT. Moreover, it showed significant synergistic improvements in piezoelectric, dielectric, and electric-field-induced strain properties. At the doping level of about x = 0.16 mol, the key performance metrics of the piezoelectric ceramics were optimal. The d33 at room temperature reached ∼447 pC/N, kp ∼0.49, and εr ∼4649. Under an applied electric field of 10 kV/cm, Spos was ∼0.092 %, and d33∗ was ∼895 p.m./V. Therefore, this study provides new insights into the progress of advanced lead-free piezoelectric materials for multifunctional applications.

Strain evolution from the ferroelectric to the relaxor state in (0.67 - x)BiFeO3-0.33BaTiO3-xBi(Mg0.5Zr0.5)O3 lead-free ceramics.

The BiFeO3-BaTiO3 solid solution exhibits enhanced electric properties due to its modified phase structure with relaxor characteristics and reduced leakage current. Despite these advancements, the underlying mechanism behind the phase transition from a ferroelectric to a relaxor state in BF-BT ceramics remains largely unexplored. Here, the evolution of strain in (0.67 - x)BiFeO3-0.33BaTiO3-xBi(Mg0.5Zr0.5)O3 ceramics is investigated, with a focus on the strain transition from a ferroelectric to a relaxor phase. A strengthening of relaxor behavior is observed in the modified rhombohedral (R) and pseudocubic (PC) phase structure, resulting in optimal strain (Suni = 0.25%, Spos = 0.24%) at x = 0.04. The enhanced strain is attributed to the promotion of domain switching and the presence of strong random fields, with polar nanoregions integrating into a long-range ordered matrix. Furthermore, a gradual increase in strain with rising temperature is noted, driven by increased polarization and the expansion of ferroelectric domains. This study underscores the critical role of structural modifications in augmenting the electric response of BF-BT ceramics, thereby advancing the development of lead-free piezoelectric materials.

Microwave-Assisted Fabrication and Characterization of Carbon Fiber-Sodium Bismuth Titanate Composites

Lead-based piezoelectric materials cause many environmental problems, regardless of their exceptional performance. To overcome this issue, a lead-free piezoelectric composite material was developed by incorporating different percentages of carbon fiber (CF) into the ceramic matrix of Bismuth Sodium Titanate (BNT) by employing the microwave sintering technique. The aim of this study was also to evaluate the impact of microwave sintering on the microstructure and the electrical behavior of the carbon-fiber-reinforced Bi0.5Na0.5TiO3 composite (BNT-CF). A uniform distribution of the CF and increased densification of the BNT-CF was achieved, leading to improved piezoelectric properties. X-ray diffraction (XRD) showed the formation of a phase-pure crystalline perovskite structure consisting of CF and BNT. A Field Emission Scanning electron microscope (FESEM) revealed that utilizing microwave sintering at lower temperatures and shorter dwell times results in a superior densification of the BNT-CF. Raman Spectroscopy confirmed the perovskite structure of the BNT-CF and the presence of a Morphotropic Phase Boundary (MPB). An analysis of nanohardness indicated that the hardness of the BNT-CF increases with the increasing amount of CF. It is also revealed that the electrical conductivity of the BNT-CF at a low frequency is significantly influenced by the amount of CF and the temperature. Moreover, an increase in the carbon fiber concentration resulted in a decrease in dielectric properties. Finally, a lead-free piezoelectric BNT-CF showing dense and uniform microstructure was developed by the microwave sintering process. The promising properties of the BNT-CF make it attractive for many industrial applications.

Thermodynamic potential construction and biaxial stress analysis of K0.4Na0.6NbO3 single crystals

The macroscopic properties of piezoelectric materials can be profoundly influenced by stress. In this research, thermodynamic potential parameters of K0.4Na0.6NbO3 (KNN) single crystals have been experimentally quantified to assess the effects of stress. Leveraging the Landau thermodynamic potential theory, it has been identified that the application of biaxial tensile stress causes a significant elevation in both the piezoelectric property and phase transition temperature in KNN crystals. This transition remarkably extends their working range and improves the material's applicated potential. The coherence between these computational outcomes and experimental data—from the strategic growth of KNN single crystals with internal stress—underscores the reliability of our findings (dielectric constant from 213 to 1274, TO-T from 180 to 234 °C). Additionally, theoretical calculation predicts a potential enhancement in the piezoelectric capabilities of KNN single crystals. This study provides valuable insights for the growth of high-quality piezoelectric crystals and further promotes the application of lead-free piezoelectric materials.

High-piezoelectric lead-free BiFeO3–BaTiO3 ceramics with enhanced temperature stability and mechanical properties

BiFeO3–BaTiO3 (BF–BT) ceramics exhibit higher piezoelectric coefficients (d33), Curie temperatures (TC), and temperature stability than other high-temperature lead-free piezoelectric materials. However, despite their crucial role in piezoelectric devices, the mechanical properties of BF–BT ceramics have been underexplored. A thorough evaluation of the mechanical properties of BF–BT is crucial for developing cost-effective and durable lead-free piezoelectric ceramics. Moreover, the specific causes of the high piezoelectric response and excellent temperature stability of BF–BT ceramics remain unclear owing to the instrumental detection threshold, which limits experimental studies to temperatures above 140 °C and below the degradation temperature of d33. To investigate the intrinsic origins of the high piezoelectricity and temperature stability of BF–xBT ceramics and to enhance their mechanical properties, a two-step sintering process is used to fabricate these ceramics (0.25 ≤ x ≤ 0.40). Owing to improvements in grain refinement and reduced Bi3+ volatilization, the BF–0.33BT ceramic exhibits enhanced overall performance, with a modified small punch strength of 155 MPa, Vickers hardness of 5.2 GPa, a d33 of 220 pC/N at room temperature, TC of 466 °C, and d33 values exceeding 400 pC/N at 260 °C. Phase-field simulations, which address the limitations of device detection thresholds, reveal that with increasing temperature, the domain structure relaxes, and polarization intensity decreases. This indicates that changes in the high-temperature piezoelectric properties can be attributed to domain structure relaxation and the increase in dielectric constant. Overall, BF–BT ceramics exhibit superior piezoelectric performance, mechanical properties, and temperature stability, making them highly suitable for use in high-temperature and demanding environments.

Improvement the dielectric and impedance properties of Pb-free Bi0.5Na0.5TiO3-SrTiO3 piezoelectric materials modified by Fe2O3

The focus of this study is on the Fe2O3-doped Bi0.5Na0.5TiO3-SrTiO3 piezoelectric material. This is important to find ecologically acceptable piezoelectric materials. This research aims to obtain a lead-free piezoelectric material because lead is a material that is not environmentally friendly. An alternative solution is a piezoelectric material based on BNT-ST, which in this case is doped with Fe2O3 material. The study of Fe2O3 doped Bi0.5Na0.5TiO3-SrTiO3 piezoelectric material prepared by the solid-state reaction method was carried out to determine the optimum composition of the material formed. Doping variations are 0; 2.5; 5; 7.5; and 10 in mol %. The examinations were performed using X-ray diffraction (XRD) spectroscopy, a Scanning Electron Microscope (SEM), and an LCR meter. The Fe2O3 doped Bi0.5Na0.5TiO3-SrTiO3 produced a new compound in the form of FeBi5Ti3O15-Na2Ti3O7-SrTiO3 with the crystal structure of cubic, orthorhombic, and monoclinic, as well as the increasing crystalline size with the addition of dopants, exclude at 5 mol % and 7.5 mol %. FeBi5Ti3O15-Na2Ti3O7-SrTiO3 also produces varying particle sizes, which are between 0.88–8.23 µm. From the obtained data, the optimum composition of Fe2O3 doped Bi0.5Na0.5TiO3-SrTiO3 was the 2.5 mol % of Fe2O3 due to it having the highest dielectric constant (er ) and temperature Curie (Tc ), and also the lowest material impedance (Z) with the er of 12.037 at Tc of 400 °C and Z of 135 kΩ. The high piezoelectricity, which is indicated by the high value of the dielectric constant and Curie temperature, is possible due to the presence of a greater number of sodium ions in the Na2Ti3O7 phase. Sodium ions are ions with good electrical storage capabilities. The increase in dielectric constant in the BNT-ST piezoelectric obtained by the addition of Fe2O3 shows that this material can be used as a substitute for lead-based piezoelectric materials so that it is secure for the environment. The piezoelectric material of BNT-ST doped with Fe2O3 earned from this research can be applied to obtain electricity with a optimal value when given mechanical pressure

Effect of stirring and KOH/NaOH ratio on phase formation in hydrothermal synthesis of KNbO3-NaNbO3 particles

This study investigates the hydrothermal synthesis of KNbO3-NaNbO3 particles, which contains compositions of interest as lead-free piezoelectric materials. Precursor solutions containing Nb2O5, NaOH/KOH were hydrothermally reacted at 190 0C for 15 hours using either a conventional reactor or a reactor with stirring. For 50 % KOH or lower, the product was cubic or elongated cuboid/belt-shaped NaNbO3, whereas solely KOH resulted in hexagonal plate-like KNbO3. When 75 % KOH was used, the product was a mixture of large K5Na3Nb6O19·9 H2O hexagonal plates and smaller NaNbO3 cubes. We hypothesized this phase segregation was induced by highly concentrated microenvironments, and stirring would prevent that. Accordingly, stirring hydrothermal treatment of 75 % KOH solution produced only K5Na3Nb6O19·H2O hexagonal plates, which could be transformed to K0.7Na0.3NbO3 by calcination. By reducing the hydrothermal treatment time to 1 – 6 hours we isolated reaction intermediates, and based on them propose a kinetics-controlled mechanism for hydrothermal reactions of Nb2O5 and KOH/NaOH.

0.98(K0.5Na0.5)NbO3–0.02(Bi0.5Na0.5)(Zr0.85Sn0.15)O3 Single Crystals Grown by the Seed-Free Solid-State Crystal Growth Method and Their Characterization

(K0.5Na0.5)NbO3-based single crystals are of interest as high-performance lead-free piezoelectric materials, but conventional crystal growth methods have some disadvantages such as the requirement for expensive Pt crucibles and difficulty in controlling the composition of the crystals. Recently, (K0.5Na0.5)NbO3-based single crystals have been grown by the seed-free solid-state crystal growth method, which can avoid these problems. In the present work, 0.98(K0.5Na0.5)NbO3–0.02(Bi0.5Na0.5)(Zr0.85Sn0.15)O3 single crystals were grown by the seed-free solid-state crystal growth method. Sintering aids of 0.15 mol% Li2CO3 and 0.15 mol% Bi2O3 were added to promote single crystal growth. Pellets were sintered at 1150 °C for 15–50 h. Single crystals started to appear from 20 h. The single crystals grown for 50 h were studied in detail. Single crystal microstructure was studied by scanning electron microscopy of the as-grown surface and cross-section of the sample and revealed porosity in the crystals. Electron probe microanalysis indicated a slight reduction in K and Na content of a single crystal as compared to the nominal composition. X-ray diffraction shows that the single crystals contain mixed orthorhombic and tetragonal phases at room temperature. Raman scattering and impedance spectroscopy at different temperatures observed rhombohedral–orthorhombic, orthorhombic–tetragonal and tetragonal–cubic phase transitions. Polarization–electric field (P–E) hysteresis loops show that the single crystal is a normal ferroelectric material with a remanent polarization (Pr) of 18.5 μC/cm2 and a coercive electrical field (Ec) of 10.7 kV/cm. A single crystal presents d33 = 362 pC/N as measured by a d33 meter. Such a single crystal with a large d33 and high Curie temperature (~370 °C) can be a promising candidate for piezoelectric devices.

Synergistic design strategy for enhancing the piezoelectric performance of BiFeO3-Based high-temperature piezoelectric ceramics

A novel synergistic strategy was used to improve the piezoelectric characteristics of high-temperature piezoelectric ceramics. This work combined three commonly used strategies, constructing the Morphotropic Phase Boundary to reduce energy barriers, changing domain structures impacting macroscopic piezoelectric properties, and adjusting BO6 octahedral distortions reflecting microstructural changes, thus effectively regulating the piezoelectric behaviors of BiFeO3-based ceramics. As a result, the 0.67BiFeO3-0.32BaTiO3-0.01BiAlO3 component, exhibiting the maximum distortion of the BO6 octahedron and the coexistence of macrodomains and nanodomains, achieved the optimal piezoelectric characteristics (d33 = 225 ± 10 pC N−1, TC = 450 °C). Additionally, the ceramic maintained its high piezoelectric properties even at temperatures as high as 280 °C (346 pC N−1). This study presents a novel collaborative design strategy that combines phase structure, domain structure, and BO6 octahedral distortion, significantly enhancing the development potential of lead-free high-temperature piezoelectric materials in the future.

Theoretical study on multi-physics coupling problems of functionally-graded lead-free piezoelectric rectangular thin plates

This paper carried out a theoretical research on multi-physics coupling problems of functionally-graded lead-free piezoelectric rectangular thin plates. Firstly, the perturbation theory was used to study the bending problem of functionally-graded lead-free piezoelectric rectangular thin plates, and the nonlinear governing equations for this bending problem were established. Then, the three piezoelectric coefficients reflecting the piezoelectric property were taken as the perturbation parameters, and the nonlinear governing equations were transformed into multiple sets of linear equations by the multi-parameter perturbation method. Finally, the solutions of these linear equations were solved by the semi-inverse solving method. Based on the finite element simulations, the effectiveness of the perturbation solutions obtained here was verified. The research results showed that it was reasonable to choose three piezoelectric coefficients as perturbation parameters, which was accord with the basic idea of perturbation theory. The analysis results indicated that there was a cross transfer relationship between external loads and perturbation solutions of every order, which could be used to simplify the perturbation expansion. Moreover, the deformation of the functionally-graded lead-free piezoelectric thin plate was less than that of the functionally-graded thin plate, that is, piezoelectric properties in lead-free piezoelectric materials had a piezoelectric enhancement effect.

Effects of doping with selected rare-earth elements (Eu3+, Dy3+, Eu3+/Dy3+) on the structural characteristics as well as electrical and luminescent properties of K0.5Na0.5NbO3

The effects of adding Eu3+, Dy3+, and Eu3+/Dy3+ rare-earth elements on the microstructural, optical and electrical properties of lead-free piezoelectric materials based on K0.5Na0.5NbO3 (KNN) were investigated. A series of fine powders were synthesized via a modified Pechini route utilizing citric acid. Relatively large amounts of rare-earth elements were successfully incorporated into the crystal lattice of KNN. A combination of X-ray diffraction, X-ray absorption spectroscopy, energy-dispersive X-ray and scanning electron microscopy were used to characterize the structure and chemical composition of the powders and sinters. XRD patterns indicated the formation of a single-phase orthorhombic structure in the co-doped sinter. X-ray absorption spectroscopy revealed the nominal 3+ valence states of Eu and Dy in KNN ceramic sinters. The Mott model and group symmetry theory were used to discuss the characteristics of Raman spectra obtained for the EuDy:KNN ceramics. The ceramics exhibited good dielectric permittivity (ε≃1300) and low dielectric loss (tan δ=0.03) in the temperature range of 170–240°C. The electrical properties of the ceramics showed that the basic mechanism of conduction and relaxation was thermal activation, and that small polaron hopping was responsible for charge carrying. The Eu3+ and Dy3+ ions displayed characteristic red and orange emissions in sinters when excited with light in the wide ultraviolet spectra range (380–420 nm).

The influence of thermo-electromechanical coupling on the performance of lead-free BNT-PDMS piezoelectric composites

In recent times, there have been notable advancements in haptic technology, particularly in screens found on mobile phones, laptops, light-emitting diode (LED) screens, and control panels. However, it is essential to note that the progress in high-temperature haptic applications is still in the developmental phase. Due to their complex phase and domain structures, lead-free piezoelectric materials such as Bi0.5Na0.5TiO3 (BNT)-based haptic technology behave differently at high temperatures than in ambient conditions. Therefore, it is essential to investigate the aspects of thermal management and thermal stability, as temperature plays a vital role in the phase and domain transition of BNT material. A two-dimensional thermo-electromechanical model has been proposed in this study to analyze the thermal stability of the BNT-PDMS composite by analyzing the impact of temperature on effective electromechanical properties and mechanical and electric field parameters. However, the thermo-electromechanical modelling of the BNT-PDMS composite examines the macroscopic effects of the applied thermal field on mechanical and electric field parameters, as phase change and microdomain dynamics are not considered in this model. This study analyzes the impact of thermo-electromechanical coupling on the performance of the BNT-PDMS composite compared to conventional electromechanical coupling. The results predicted a significant improvement in piezoelectric response compared to electromechanical coupling due to the increased thermoelectric effect in the absence of phase change and microdomain switching for temperature boundary conditions below depolarization temperature ( Td∼200∘ C for pure BNT material).

Impact of defect concentration on piezoelectricity in Mn/Fe-doped KTN crystals

Defect engineering via doping exhibits considerable potential for improving the performance of environment-friendly lead-free piezoelectric materials. Owing to the susceptibility to lattice vibrations and the micro-local chemical environment, the readily available Mn/Fe transition metal elements (TMEs) facilitate the construction of defect structures. However, the role of TMEs in shaping the domain structures and the corresponding promotional mechanism of piezoelectricity need to be further decoded. Herein, we propose the different influence mechanisms of Mn and Fe ions on the ferroelectric domain and piezoelectric properties. Different concentrations of (MnNb/Ta′-VO••)• and (FeNb/Ta″-VO••)× defect dipoles are obtained based on the synergy of Mn/Fe ions with oxygen vacancies. Diverse ferroelectric behaviors resulting from (MnNb/Ta′-VO••)• and (FeNb/Ta″-VO••)× defect dipoles are observed. Furthermore, the variation of the dielectric diffusiveness with the defect dipole concentration is investigated. Trace concentration of (MnNb/Ta′-VO••)• generates strong diffusiveness. With the characterization of the ferroelectric domain, this strong diffusiveness is attributed to the lattice-like domain structure. Thereafter, the mechanisms of Mn/Fe defect dipoles on the formation of domain structures are clarified. Macroscopically, the dielectric and piezoelectric properties are measured with Mn/Fe ion components. Trace Mn doping and the resulting lattice-like domain significantly enhance the piezoelectric coefficient, resulting in an increase of nearly 50% for K(Ta,Nb)O3 single crystals. This work highlights the tremendous potential of TME-induced defect dipoles for modifying the ferroelectric domain and provides a reference paradigm for improving piezoelectricity through defect engineering.

Boosting tetracycline degradation of BaTiO3-based piezo-catalysts via modulating phase boundary and band structure

Piezoelectric catalysis, which converts mechanical energy into chemical activity, has important applications in environmental remediation. However, the piezo-catalytic activity of various piezoelectric materials is limited by the weak piezoelectricity as well as the mismatched band-gap, leading to inefficient electron-hole pair generation and difficult carrier migration. Here, a simple strategy combining phase boundary and energy band structure modulation was innovatively proposed to enhance the piezo-catalytic activity of BaTiO3 ferroelectric by Ce ions selecting different doping sites. Thanks to the coexistence of tetragonal (P4mm) and orthorhombic (Amm2) phases effectively flattened the Gibbs free-energy and thus enhanced the piezoelectric activity, as well as suitable energy bandwidth facilitating the carrier migration were realized in the B-sites doped Ba(Ti0.95Ce0.05)O3. The degradation rate constant k of tetracycline (TC) was high to 30.56 × 10-3 min−1, which was 2.03 times higher than that of pure BaTiO3 and superior to most representative lead-free perovskite piezoelectric materials. Theoretical calculations validated that the charge density and high O2 and OH– adsorption energy on the Ba(Ti0.95Ce0.05)O3 surface promoted more efficient •O2– and •OH radicals conversion and bettered response to piezo-catalytic reaction. This work is important to design high-performance piezo-catalysts by synergistic regulation of phase boundary and energy band structure in perovskite materials for long-term antibiotic tetracycline removal.

Investigation of the crystal-oriented behavior of rare earth substituted Sr2NaNb5O15 lead-free piezoelectric materials under a high magnetic field

The crystal-orientation behavior of Sr2NaNb5O15 (SNN) lead-free piezoelectric materials under a magnetic field was investigated by substituting rare-Earth elements (Ln = Nd, Eu, Ho, Yb), which were selected based on their ionic radii and magnetic or non-magnetic ions. The magnetic ions, Nd, Ho, and Yb, did not affect the magnetic anisotropy of the SNN. The nonmagnetic ions (Eu3+) changed from the a, b-axis orientation to the c-axis orientation in the direction of the magnetic field. The Eu-substituted SNN powders revealed that the degree of orientation of the c-axis increased as the Eu content increased. Consequently, c-axis-oriented Eu-substituted SNN ceramics were obtained with the degree of orientation of 0.9. The diamagnetism along the a, b-axis became larger than that along the c-axis owing to a decrease in the c-axis lattice constant. By substituting Eu with SNN, the piezoelectric properties decreased as the hardening of SNN progressed.

Kesan Penggantian Litium ke atas Struktur, Sifat Fizikal dan Sifat Elektrik terhadap Seramik BCZT

The invention of novel lead-free piezoelectric materials with ABO3 perovskite structure, based on barium calcium zirconate titanate (BCZT) for application in various device especially in sensor application. In this work, BCZT with lithium substitution at the calcium site with composition Ba0.85Ca0.15-xLi2xZr0.1Ti0.9O3 (x = 0.00, 0.03, 0.06, 0.09 and 0.12) were synthesized by using the conventional, solid state reaction method. The influence of different Li content on the structure, microstructure, density, and electrical properties were investigated. The results show that substitution led to the improvement of the physical and electrical properties of the piezoelectric ceramic materials. The physical properties show the largest grain size and the highest value of density, ρ which is 4.158 g/cm3 for x = 0.06. This physical properties led to the highest value of piezoelectric coefficient, d33, remnant polarisation, Pr and saturated polarization, Ps which are 304.6 pC/N, 3.27 µC/cm2, and 5.54 µC/cm2, respectively, while the highest dielectric constant, ɛr was 3994 when x = 0.12.