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

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

Fabrication and Properties of 2-2 Cement Based Piezoelectric Composites

Composites with 2-2 connectivity were fabricated from lead magnesium niobate-lead zirconate-lead titanate(PMN) and sulphoaluminate cement by cut-filling process. The influences of PMN volume fraction and water/cement ratio on the properties of the composite were investigated. The results show that the piezoelectric strain constant d₃₃ increase rapidly with increasing volume fraction of PMN. When the PMN volume fraction is about 0.60, the d₃₃ value is up to 357 pCN^-1. The planar electromechanical coupling coefficient K_p of the composites is lower than that of PMN ceramic, while the thickness electromechanical coupling coefficient K_t is higher than that of PMN ceramic. The water/cement ratio has little influence on piezoelectric properties of 2-2 cement based piezoelectric composite.     

An experimental model for predicting the piezo and dielectric constant of PVDF-PZT nanocomposite fibers with 0–3 and 1–3 connectivity

Energy harvesting from mechanical energy around ambient by flexible nanogenerators is one of the most efficient ways to generate green and renewable energy. Lead zirconate titanate (PZT) particles were embedded into a polyvinylidene fluoride (PVDF) polymer matrix to prepare mixed 0–3 and 1–3 connectivity nanocomposite fibers by electrospinning method. Various theoretical models of Maxwell-Garnett, Rayleigh, and Tinga etc were presented at two different Classes to predict the dielectric constant of PVDF-PZT nanocomposite fibers and compared the predicted results with the experimental results. Also, the piezoelectric properties like the piezoelectric coefficient (d₃₃) and piezoelectric voltage coefficient (g₃₃) were predicted by the Furukawa model and the predicted values were compared with the experimental values. Finally, the experimental model was derived to predict the dielectric constant of binary composites with mixed 0–3 and 1–3 connectivity. Compared to well-known models, the proposed experimental model accurately predicted the dielectric constant of PVDF-PZT nanocomposite fibers. The highest and lowest difference between the theoretical and the experimental results were obtained 12.24% and 0.12% for PZT volume fractions 1.1 and 17, respectively. Also, due to the linear relationship between the dielectric constant and piezoelectric coefficients, this model was generalized to predict the piezoelectric coefficients.     

Achieving both large transduction coefficient and high Curie temperature of Bi and Fe co-doped PZT piezoelectric ceramics

Achieving both the large transduction coefficient (the product of piezoelectric charge d₃₃ and voltage coefficients g₃₃) and high Curie temperature is very important to improve the power generation performance and their thermal stability of piezoelectric energy harvesters. It is difficult to improve the transduction coefficient of the commercial PZT based piezoelectric ceramics due to the same variation trend of piezoelectric charge coefficient and dielectric constant with chemical modifications. In this work, Bi₂O₃ and Fe₂O₃ co-modified ((Pb_1-xBi_x)((Zr_0.53Ti_0.47)_1-xFe_x)O₃) ceramics were prepared by conventional solid state reaction method, and their dielectric and piezoelectric properties were studied. The piezoelectric charge coefficient d₃₃ increases by Bi and Fe co-modifications due to the enlarged grain size and reduced lattice distortion, while the dielectric constant ε₃₃ deceases mainly owing to the increased micro-pores in grains, leading to the enhancement transduction coefficient d₃₃×g₃₃. The Curie temperature Tc and maximum transduction coefficient d₃₃×g₃₃ are 346 °C and 17169 × 10^?15 m²/N, respectively, which are both higher than those of commercial PZT and PZN-PZT based piezoelectric ceramics. This work provides a new way to enhance the transduction coefficient of PZT based ceramics for piezoelectric energy harvesters used in wide temperature range.     

Dielectric and piezoelectric properties of PMN-PT ceramics doped with strontium

Motivated by the need of piezoelectric ceramics with enhanced piezoelectric properties, we investigated the effects of Sr addition on the structural, dielectric and piezoelectric properties of PMN-PT ceramics. The synthesis of (1-x)[(Pb_1?ySr_y)(Mg_1/3Nb_2/3)O₃]-x(Pb_1?ySr_yTiO₃) (PsMN–PsT) (y: 0 ? 0.10, x: 0.35 – 0.40) ceramics was carried out by the colloidal coating method to distribute Sr uniformly in PMN and PT respectively. When x=0.35, it was found that y=0.02 gave the optimal piezoelectric properties. Furthermore, by keeping y=0.02 and varying x, it was found that x=0.37 gave even better piezoelectric properties with the optimal piezoelectric strain coefficient d₃₃ (630 pC/N), piezoelectric coupling factor k_p (0.52), dielectric constant ε_r (4000), and Curie temperature T_c (210 °C), exhibiting great potential for actuator and sensor applications.     

Reduced dielectric loss and high piezoelectric constant in Ce and Mn co-doped BiScO3-PbCexTi1-xO3-Bi(Zn0.5Ti0.5)O3 ceramics

MnO₂-doped 0.99(0.36BiScO₃-0.64PbTi_1-xCe_xO₃)-0.01Bi(Zn_0.5Ti_0.5)O₃ (BS-PTC-BZT-MnO₂) ceramics are fabricated by the solid-state method. Here, it's firstly reported that Ce element can reduce dielectric loss (tan δ) and suppress the decrease of piezoelectric constant (d₃₃) simultaneously. Effects of Ce contents on the structure and electrical properties of BS-PTC-BZT-MnO₂ ceramics are studied. The ceramics (x?=?0.02) with MPB (rhombohedral-tetragonal) possess low dielectric loss (tan δ?=?1.36%, 1?kHz) and high piezoelectric constant (d₃₃ =?360 pC/N) simultaneously, which is superior to most reported BS-PT. Besides, excellent comprehensive properties including high Curie temperature (T_C =?422?°C), large dielectric constant (?_r =?1324), and high remnant polarization (P_r =?35.1?µC/cm²) are obtained. Asymmetric S-E and P-E hysteresis loops indicate that defects and oxygen vacancies are induced by multi-valence elements (Ce and Mn), which is the origin for reducing tan δ. In addition, good thermal stability of piezoelectric and dielectric properties is observed. These results indicate that Ce and Mn co-doped BS-PTC-BZT-MnO₂ ceramics can be well applied as power electronic devices under high temperature.     

Enhanced dielectric and piezoelectric properties in potassium sodium niobate/polyvinylidene fluoride composites using nano-silicon carbide as an additive

Piezoelectric materials are an indispensable part of modern life. Yet the existing environmental issues with conventional lead-based piezoelectrics has motivated scientist to develop novel substitutes including lead-free piezoelectric polymer composites. Following this path, the present research has focused on the fabrication of ternary composites of Polyvinylidene fluoride (PVDF)/Potassium Sodium Niobate (KNN)/nano-Silicon carbide (SiC) via hot compression molding and studying the effect of additives on the PVDF structure and the electrical properties of the composite. The obtained scanning electron micrographs and density measurements showed that the fabrication method provided dense samples. The activated polarization phenomena in the prepared samples enhanced dielectric permittivity and dielectric loss at a constant frequency with increasing KNN and SiC contents. Besides the expected dipole polarization, the presence of interfaces in the composites gave rise to the Maxwell–Wagner–Sillars effect and its corresponding polarization phenomenon. The semiconductive nature of SiC also promoted space charge polarization. However, these properties were frequency-dependent because the first two polarization mechanisms are deactivated at high frequencies. XRD patterns showed that SiC addition can alter the primary crystalline structure of PVDF and promote β-phase formation in the poled samples. Piezoelectric measurements confirmed the significant role of SiC addition to PVDF-KNN composites. The most significant increase in the piezoelectric properties was observed in PVDF-60KNN-1SiC, with a 183% increase in d₃₃ value. The PVDF-80KNN-1SiC had the highest d₃₃ value of 30.5 pC/N. It also had the best piezoelectric voltage coefficient and hence the highest figure of merit. Higher SiC contents restrict the efficiency of poling by forming a conductive path across the sample which would deteriorate the piezoelectric performance of the material. The present findings show that PVDF-KNN-SiC composites can be considered as a potential flexible piezoelectric material for future applications.     

Significantly improved dielectric and piezoelectric properties by defects in PbNb2O6-based piezoceramics

PbNb₂O₆ (PN)-based piezoceramics are considered important materials used in high temperatures. Whereas, the main problem of PN-based ceramic is its low electrical performance such as piezoelectric constant (d₃₃), severely restricting its practical applications. Here, based on the principle of regulating structure and performance via defect engineering, a new way of artificially tailoring point defects by A-site nonstoichiometry is implemented in this study. The results show that the PN-based ceramics with A-site deficiency exhibit significantly enhanced dielectric and piezoelectric properties. Particularly, the relative dielectric permittivity (ε_r) increased by 165% (from 197 to 523) and the d₃₃ increased by 177% (from 30 to 83 pC/N) while maintaining a high Curie temperature (T_C ~ 543 °C), and the resultant superior comprehensive performance is nearly highest in PN-based ceramic system. The X-ray photoelectron spectrometer and Raman spectra reveal that A-site deficiency leads to a decreased level of oxygen vacancies and NbO₆ octahedral distortion as well as disorderly motions of A-site cations, which further causes the markedly decreased domain size exhibited in piezoresponse force microscopy (PFM) images. Consequently, the improved domain structure gives rise to improved dielectric and piezoelectric properties. The results of this work provide a simple and effective strategy to improve the dielectric and piezoelectric properties while keeping a high T_C in the PN-based ceramics system, meeting the urgent demands of high-temperature applications.     

Piezoelectric properties and microstructure of ceramicrete-based piezoelectric composites

Inorganic piezoelectric ceramic composite is the potential sensing element for long-term structural health monitoring due to its excellent durability and compatibility. In this study, a Ceramicrete-based piezoelectric composite is proposed preliminarily, in which the magnesium potassium phosphate cement is used as the matrix and the lead zirconate titanate particle is utilized as the functional phase. Piezoelectric properties test and microstructure analysis are performed to evaluate the testing samples. Results show that the piezoelectric performance of the composite increase with the increase of piezoelectric ceramic particle size. The value of the piezoelectric strain factor (d₃₃) can reach 83.8 pC/N, while the corresponding piezoelectric voltage factor (g₃₃) is 50.1 × 10^-3 V•m/N at the 50th day after polarization. Microstructure analysis illustrates that the interfacial transition zone (ITZ) between the matrix and the particles is dense. Moreover, the influence of aging on the composite is attributed to the continuous hydration after polarization. It indicates that the composites have a higher piezoelectric performance, which can be regarded as a promising sensing element material.     

PU/CB/PZT压电阻尼复合材料极化条件的研究

以导电碳黑(CB)为导电相、压电陶瓷(PZT)为压电相、聚氨酯(PU)为基体制备了一系列的压电阻尼复合材料(PU/CB/PZT)。研究了CB、PZT对所制备材料的耐击穿性能的影响,探讨了材料的压电性能和阻尼性能随PZT含量以及极化时间的变化规律。结果表明,PU/CB/PZT压电阻尼复合材料的压电常数随PZT含量和极化时间增加而增加,当极化场强选为5 kV/mm、极化时间30 min、PU/CB/PZT质量份为100/4/80时,材料的压电性能最佳,达到45.7 PC/N。随着PZT用量和极化时间增加,压电阻尼复合材料的阻尼因子峰值提高。     

Investigations on electric properties and domain structures of Nd-doped 0.70Pb(Mg1/3Nb2/3)O3–0.30PbTiO3 relaxor ferroelectric ceramics with high piezoelectric properties

Although rare earth neodymium (Nd) doping is common in Pb(Mg1/3Nb2/3)O₃–PbTiO₃ (PMN–PT) single crystals, it is rarely reported in PMN–PT ceramics. To explore the effect of Nd doping on PMN–PT ceramics, PMN–30PT:xNd³⁺ (x = 0%, 1%, 2%, and 3%) relaxor ferroelectric ceramics were fabricated using a solid-state method via two-step sintering. An enhanced piezoelectric charge coefficient (d₃₃) of ∼870 pC/N and a high piezoelectric strain coefficient (d₃₃*) of ∼1025 pm/V were achieved for x = 2%. Through Rayleigh analysis of polarization–electric field (P–E) hysteresis loops under small electric fields, it was found that the dielectric property was mainly influenced by the intrinsic contribution (local lattice distortion). Furthermore, by investigating domain configurations, high piezoelectric properties were found to be associated with the domain size reduction and local structural heterogeneity. The results indicate that the PMN–30PT:xNd³⁺ ceramics is a promising material for electronic devices, and that rare earth Nd doping is an efficient strategy for improving the electronic performance of Pb-based relaxor ferroelectrics.     

Matrix influence on the piezoelectric properties of piezoelectric ceramic/polymer composite exhibiting particle alignment

This study was addressed to the influence of an electric field strength applied at fabrication process and matrix properties, such as the dielectric constant and the Young's modulus, on “pseudo‐1‐3 piezoelectric ceramic/polymer composite” in order to further enhance the piezoelectricity of that. The pseudo‐1‐3 piezoelectric ceramic/polymer composite consists of linearly ordered piezoelectric ceramic particles in polymer material. Silicone gel, silicone rubber, urethane rubber, and poly‐methyl‐methacrylate, which exhibit different dielectric constants and Young's modulus, were used as matrices to evaluate the matrix influence. The piezoelectricity of the pseudo‐1‐3 piezoelectric ceramic/polymer composite was evaluated using the piezoelectric strain constant d₃₃. The d₃₃ is one of the indices of the piezoelectric properties for piezoelectric materials. As a result, it was confirmed that d₃₃ of the pseudo‐1‐3 piezoelectric ceramic/polymer composite increased with the increase of the electric filed strength applied at fabrication process, though, it reached a constant value at a certain strength value. Further it was confirmed that dielectric constant of the matrix had a small influence on d₃₃ of the pseudo‐1‐3 piezoelectric ceramic/polymer composite, however, in case of matrix of lower Young's modulus, d₃₃ was increase. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41817.     

Microstructure,dielectric and piezoelectric properties of 0–3 lead free barium zirconate titanate ceramic-Portland fly ash cement composites

Piezoelectric ceramic – Portland cement composites have been developed for sensor application in concrete structures to overcome the acoustic matching problem that may occur for piezoelectric ceramic or polymers with concrete. Pozzolanic materials such as fly ash are commonly used in concrete to enhance durability. The objectives of this research were to investigate the effects of fly ash addition on the physical properties, dielectric properties and piezoelectric properties of 0–3 barium zirconate titanate ceramic– Portland cement composites. The results showed that the dielectric constant of these composites decreased when the fly ash content in the composite increases. However, the piezoelectric coefficient (d₃₃) value of BZT–PC composite with fly ash 10% by volume was found to be similar to that of BZT–PC composites.     

Effects of Carbon Nanofiber on Dielectric Properties of PMN/CNFs/EP Composites

A kind of new composite material composed of piezoelectric ceramic lead magnesium niobate-lead zirconate-lead titanate (PMN)/carbon nanofibers (CNFs)/epoxy resin (EP) were prepared by a resin casting method. The effects of carbon nanofibers on dielectric properties of PMN/CNFs/EP composites were investigated in this paper. The concetration of CNFs had significant effects on dielectric constant, dielectric loss, dielectric frequency dependence and dielectric temperature dependence of PMN/CNFs/EP composites. When the content of CNFs increased from 0 to 0.8 wt% of the epoxy resin, the dielectric constant at 1 kHz increased sharply from 13.6 to 158, and the dielectric loss increased from 0.0524 to 2.59. In plots of the dielectric constant against frequency and dielectric loss against frequency, the dielectric constant and dielectric loss reduced dramatically at lower frequency ranging from zero to about 10⁵ Hz, then approach to be stable at frequency higher than 10⁵ Hz. Moreover, as to the effects of temperature on dielectric constant and dielectric loss of PMN/CNFs/EP composites, the dielectric constant of composite increased ranging from 25°C to 160°C, and the dielectric loss of composite also showed increase besides that with CNFs content 0.8 wt%.     

CuO掺杂铌酸盐基无铅压电陶瓷的性能研究

采用固相反应法制备了主成分为0．94（Na0.5K0.5）NbO3—0．03LiSbO3—0．03LiNbO3（简称为NKNLS-3）的无铅压电陶瓷,探讨了掺杂不同量的CuO对材料相结构、显微结构和电学性能的影响,以期获得最佳的配方。实验结果表明：CuO的掺入使d33先降低后升高,εr显著降低,机械品质因数Qm增大。当CuO掺杂量为0．3mol%时,陶瓷样品的综合压电性能最好：d33=106pC／N,tgδ=0．054,εr=340,kp=0．29,Qm=85。     

CNT loaded PVDF-KNN nanocomposite films with enhanced piezoelectric properties

The emerging smart PVDF-based composites can compensate for the intrinsic property deficiencies in either of their components. The properties of the composite are determined by the properties of the constituents and its fabrication method. In this research, a lead-free piezoelectric ceramic, potassium sodium niobate (KNN), was used as the primary reinforcement, and MWCNTs were added to improve the electrical properties. Solution casting was used to prepare PVDF-KNN-CNT composite films. After phase and structure identification of composites using SEM, XRD, FTIR, and TGA methods, the dielectric, piezoelectric and ferroelectric properties of the products were investigated. The obtained results indicated a strong dependency of dielectric, piezoelectric, and ferroelectric properties of composites on KNN content. Samples with the highest KNN content rendered ε_r, d₃₃ and g₃₃ values of 156, 28 pC/N, and 20.32 mV m/N, respectively. Introducing a small amount of conductive CNT to primary PVDF-KNN composites can drastically affect the electrical properties by severely interfering in the charge distribution within the sample. While the dielectric constant was enhanced by increasing CNT content, both piezoelectric and ferroelectric properties showed their best behavior at a critical CNT loading. Beyond this limit, a percolation path formed, which is responsible for power consumption. At the optimum CNT amount, d₃₃ and g₃₃ reached 50 pC/N and 31.93 mV m/N, respectively. The presence of conducting CNTs gave rise to the formation of more round polarization curves with higher remnant polarization. The present findings give a prospective understanding of smart piezoelectric polymer-based composites that can be used as sensors and energy harvesters.     

Low‐temperature sintering and enhanced piezoelectric properties of random and textured PIN–PMN–PT ceramics with Li2CO3

Low‐temperature sintered random and textured 36PIN–30PMN–34PT piezoelectric ceramics were successfully synthesized at a temperature as low as 950°C using Li₂CO₃ as sintering aids. The effects of Li₂CO₃ addition on microstructure, dielectric, ferroelectric, and piezoelectric properties in 36PIN–30PMN–34PT ternary system were systematically investigated. The results showed that the grain size of the specimens increased with the addition of sintering aids. The optimum properties for the random samples were obtained at 0.5 wt% Li₂CO₃ addition, with piezoelectric constant d₃₃ of 450 pC/N, planar electromechanical coupling coefficient k_p of 49%, peak permittivity ε_max of 25 612, remanent polarization P_r of 36.3 μC/cm². Moreover, the low‐temperature‐sintered textured samples at 0.5 wt% Li₂CO₃ addition exhibited a higher piezoelectric constant d₃₃ of 560 pC/N. These results indicated that the low‐temperature‐sintered 36PIN–30PMN–34PT piezoelectric ceramics were very promising candidates for the multilayer piezoelectric applications.     

Piezoelectric Properties of a Pioneering 3‐1 Type PZT/Epoxy Composites Based on Freeze‐Casting Processing

Lead zirconate titanate (PbZr_1 ? xTi_xO₃, PZT)/epoxy composites with one‐ dimensional epoxy in PZT matrix (called 3‐1 type piezocomposites) have been fabricated by tert‐butyl alcohol (TBA)‐based directional freeze casting of PZT matrix and afterward infiltration of epoxy. The composites with PZT volume fraction ranging from 0.36 to 0.69 were obtained by adjusting initial solid loading in freeze‐casting slurry. The effect of poling voltage on piezoelectric properties of the composites was studied for various volume fraction of PZT phase. With the increasing of PZT volume fraction, relative permittivity (ε_r) increased linearly and piezoelectric coefficient (d₃₃ and d₃₁) increased step by step. The resultant composites with 0.57 PZT volume fraction possessed the highest hydrostatic piezoelectric strain coefficient (d_h) value (184 pC/N), voltage coefficient (g_h) value (13.6 × 10^?3 V/m Pa), and hydrostatic figure of merit (HFOM) value (2168 × 10^?15 Pa^?1).     

Effect of polyvinylidene fluoride on the fracture microstructure characteristics and piezoelectric and mechanical properties of 0-3 barium zirconate titanate ceramic-cement composites

Barium zirconate titanate (40−60 vol.%; BZT), Portland cement (PC) and polyvinylidene fluoride (0−7 vol.%; PVDF) were used as raw materials to produce 0–3 piezoelectric cement-based composites. The highest piezoelectric charge coefficient (d₃₃∼26-27 pC/N) was found at 50−60 vol.% BZT with 5 vol.% PVDF. Moreover, the composite with 50 vol.% BZT and 5 vol.% PVDF had the highest piezoelectric voltage coefficient (g₃₃ = 16.0 × 10⁻³ V·m/N). Scanning electron microscopy was used to investigate the morphology of the fracture surface of the composite. When PVDF was used in the composite, it was observed to fill some pores at the interface zone and within the cement phase. The elastic behaviour of PVDF could also be seen in the fracture surface, where it appeared as a stretched material different from both the BZT ceramic and cement, which are brittle materials. In addition, increasing the PVDF content led to increased fracture toughness.     

0-3型压电陶瓷/硫铝酸盐水泥复合材料的介电性能和压电性能

用压制成型法，以水泥为基体，铌镁锆钛酸铅(lead magnesium niobate-lead zireonate-lead titanate，PMN)陶瓷颗粒为功能体制备了水泥基压电复合材料。分析讨论了复合材料的压电性能和介电性能。研究了水泥水化龄期对复合材料压电性能的影响，并对其机理进行了初探。结果表明：随着PMN含量的增加，压电复合材料的压电应变常数d33和介电常数均增大；不像压电陶瓷或压电复合材料的压电性能随时问的延长而减弱，水泥基压电复合材料的压电性则是随着水泥水化龄期的延长而增加，当到达一定龄期后，压电性能趋于稳定。