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.     

Physical and mechanical properties of PVDF/KNN composite produced via hot compression molding

One of the most important lead-free piezoelectric compounds that has been studied extensively belongs to alkali niobate family, the sodium-potassium niobium (KNN) compound. In this study, KNN/PVDF composite was fabricated through hot compression molding of the components and its mechanical, thermal and electrical properties were studied. For this purpose, KNN was first synthesized by solid-state reaction during two-step calcination and its structural evolution was studied using XRD. Composite samples were prepared at different KNN to PVDF weight ratios. The powder mixture was then formed into disks by hot compression molding. The microstructure of the composite samples was investigated by SEM. The prepared samples were perfectly dense with a density in the range of 97.44% to 99.11% of the theoretical density. The thermal properties of the prepared composites were evaluated by thermogravimetric analysis and it was observed that final weight loss due to material degradation was reduced with increasing KNN weight percent. In addition, samples with higher KNN contents showed increased Young's modulus and yield strength values in compression. In order to investigate the electrical properties, the dielectric constant, dielectric loss factor, piezoelectric charge and voltage coefficients and electric polarization were studied. The results showed that the dielectric constant increased with KNN content. The same trend was observed in the piezoelectric charge coefficient and the dielectric loss factor of the PVDF/KNN composites. At 80 wt% KNN, the composite showed a distinct ferroelectric behavior with a remanent polarization of 0.255 μC/cm² and 20.5 kV/cm coercivity. According to the results of the present study, hot compression molding is an effective method for producing KNN/PVDF composites with improved mechanical and thermal properties compared to its constituents.     

Effect of heat treatment on the electrical properties of lead zirconate titanate/poly (vinylidene fluoride) composites

Ceramic/polymer composites are attracting increasing interest in materials research and practical applications due to the combination of excellent electric properties of piezoelectric ceramics and good flexibility of polymer matrices. In this case, the crystallization of the polymer has a significant effect on the electric properties of ceramic/polymer composites. Based on different heat treatment methods, the crystallization of poly(vinylidene fluoride) (PVDF) in composites of lead zirconate titanate (PZT) and PVDF can be controlled effectively. PZT/PVDF composites with various PVDF crystallizations exhibit distinctive dielectric and piezoelectric properties. When the crystallization of PVDF is 21%, the PZT/PVDF composites show a high dielectric constant (ε) of 165 and a low dielectric loss (tan δ) of 0.03 at 10³ Hz, and when the crystallization of PVDF reaches 34%, the piezoelectric coefficient (d₃₃) of PZT/PVDF composites can be up to ca 100 pC N^?1. By controlling the crystallization of PVDF, PZT/PVDF composites with excellent dielectric and piezoelectric properties were obtained, which can be employed as promising candidates in high‐efficiency capacitors and as novel piezoelectric materials. Copyright © 2010 Society of Chemical Industry     

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.     

陶瓷粉体粒度对PZN—PZT／PVDF压电复合材料性能的影响

将铌锌锆钛酸铅（PZN—PZT）压电陶瓷粉体分散于聚偏二氟乙烯（PVDF）基体中,制备出0-3型PZN—PZT／PVDF压电复合材料。文中研究了PZN—PZT陶瓷不同粒度对复合材料的压电性、介电性、铁电性的影响。结果表明,当陶瓷粒度为100～150目时,压电复合材料的综合性能最佳,压电常数d33达到23．10pC／N,剩余极化强度Pr达到5．131μC·era2,矫顽场Ec为45．7lkV·cm^-1,介电常数ε。为192．86,介电损耗tanδ为0．10。     

Influence of LNO Top Electrodes on Electrical Properties of KNN/LNO Thin Films Prepared by RF Magnetron Sputtering

Highly (001) oriented (K,Na)NbO₃ (KNN) lead‐free piezoelectric thin films were grown on LaNiO₃ (LNO)‐coated silicon by RF magnetron sputtering. The effects of the top electrodes on the electrical properties of KNN thin films were investigated. The dielectric and piezoelectric properties were remarkably improved in LNO/KNN/LNO (ε_r = 899 at 1 kHz, d₃₃ = 58 pm/V), compared with that in Pt/KNN/LNO (ε_r = 584 at 1 kHz, d₃₃ = 26 pm/V). An enhanced ferroelectricity was also obtained in LNO/KNN/LNO, with a remnant polarization of 12 μC/cm² and a maximum polarization of 23 μC/cm² at the applied field of 200 kV/cm. Besides, the temperature dependence of piezoelectricity of the films was characterized in this study.     

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。     

Enhanced Piezoelectric Properties and Thermal Stability in the (K0.5Na0.5)NbO3:ZnO Lead‐Free Piezoelectric Composites

The piezoelectric properties of (K_0.5Na_0.5)NbO₃ (KNN) are normally enhanced by chemical substitutions or doping to form solid solutions. In this study, we report that the piezoelectric properties of KNN and thermal stability of piezoelectric coefficient d₃₃ can be both enhanced by forming the composite of KNN:ZnO. The d₃₃ of KNN:0.2ZnO can be improved to 110 pC/N by introducing the ZnO nanoparticles, which is better than the pure KNN (d₃₃ = 85 pC/N). The Curie temperature (T_C = 407°C) remains well comparable to the pure KNN (T_C = 408°C). Furthermore, the thermal stability of both remanent polarization (P_r) and piezoelectric parameter (d₃₃) is improved. The enhanced thermal stability could be related to the induced built‐in electric field or the enhanced sinterability by the addition of ZnO. The present results may help to optimize the piezoelectric properties of lead‐free materials by forming composite.     

Clamping of ferroelectric PVDF to enhance the electromechanical performance of a 1–3 PMN-PT/PVDF piezoelectric composite

A group of 1–3 type piezoelectric Pb (Mg_1/3Nb_2/3)O₃-PbTiO₃/polyvinylidene fluoride (PMN-PT/PVDF) composite sheets are prepared using a complex two-step hot-pressing method. Then the molecular structure model of piezoelectric materials and an inverse piezoelectric simulation of the composites are performed to express the horizontal compression, indicating the clamping activity of ferroelectric PVDF on PMN-PT. As such, this composite sheet possesses a high dielectric permittivity (ε_r) of 560 at 100 Hz for its compacted connecting of two phases. After polarization, a very large piezoelectric coefficient (d₃₃) of 1125 pC/N and a considerable electromechanical coupling factor (k_t) of 0.43 is obtained in PMN-PT/PVDF sheet with a proper aspect ratio of 1.4 and a thickness of 2.1 mm, further indicating that promoting effect of PVDF matrix on the strain in Z-direction of PMN-PT. The result shows that ferroelectric PVDF serving as polymer matrix favors the electromechanical coupling effect, and may provide a prospect of the potential application of PMN-PT/PVDF composite in sensor or transistor for matrix ultrasonic probes.     

Effects of thickness on structures and electrical properties of K0.5Na0.5NbO3 thick films derived from polyvinylpyrrolidone-modified chemical solution

Lead-free ferroelectric K_0.5Na_0.5NbO₃ (KNN) films with different thicknesses were prepared by polyvinylpyrrolidone (PVP)-modified chemical solution deposition (CSD) method. The KNN films with thickness up to 4.9 μm were obtained by repeating deposition-heating process. All KNN thick films exhibit single perovskite phase and stronger (1 1 0) peak when annealed at 650 °C. The variation of dielectric constant with thickness indicates that there exists a critical thickness for the dielectric constant in the KNN films which should lie in 1.3–2.5 μm. The similar trend is observed for the ferroelectric and piezoelectric properties of KNN films. Both the remnant polarization P_r and the piezoelectric coefficient d₃₃ of KNN thick films increase with the film thickness and become saturated after the critical thickness.     

热压法制备压电陶瓷／聚合物复合材料及性能研究

采用热压法分别制备了PZT／PVDF,PT／PVDF O-3型压电复合材料,所得材料具有较高的压电常数和良好的可柔性加工性能。并分析了无机压电陶瓷种类、含量对复合材料介电性能和压电性能的影响。     

Improved ferroelectric,piezoelectric, and dielectric properties in pure KNN translucent ceramics by optimizing the normal sintering method

In this study, it is reported that various properties can be selectively derived in a pure (K_0.5Na_0.5)NbO₃, KNN ceramics through optimizing the sintering temperature by the conventional sintering method. High piezoelectric, ferroelectric, and dielectric properties such as d₃₃ = 127 pC/N, P_r = 31 μC/cm², and ε_r = 767 are obtained at the sintering temperature of 1100 °C. On the contrary, the specimen sintered at 1130 °C does not show high piezoelectric and ferroelectric properties, but it is translucent with a transmittance of 22% and 57% at the wavelength of 800 and 1600 nm respectively and shows a very high dielectric constant ε_r of 881. The origin of the high piezoelectric constant owes to large remanent polarization and dielectric constant, and dense microstructure with uniform distribution of large grains with the conjunction of relatively large crystal anisotropy. On the other hand, dense microstructure with almost no porosity, highly compacted grain boundaries, uniform distribution of grains, and relatively low crystalline anisotropy are responsible for the translucency and large dielectric constant of the ceramic specimens. This study demonstrates that the lead-free KNN ceramic has the potential to show multiple noteworthy properties such as piezoelectric, ferroelectric, dielectric, and transparent properties. This work provides a pure KNN ceramic simultaneously with high piezoelectric and transparent characteristics prepared only by using the conventional sintering method at a moderate sintering temperature for the first time in the literature.     

Effects of pore shape and porosity on the properties of porous PZT 95/5 ceramics

Porous lead zirconate titanate (PZT 95/5) ferroelectric ceramics were prepared by sintering compacts consisting of PZT and pore formers. The piezoelectric, dielectric and ferroelectric properties of porous PZT ceramics were investigated as a function of pore shape and porosity. Piezoelectric coefficient (d₃₃), dielectric constant (ɛ₃₃) and remnant polarization (P_r) decreased with an increase in porosity, and the porous PZT ceramics with spherical pores exhibited better properties than that with irregular pores. Furthermore, the electrical conductivities of PZT ceramics were investigated to explain the phenomena that porous PZT ceramics exhibited lower dielectric loss (tan δ) than dense PZT ceramics in the temperature range from 250 to 500 °C.     

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.     

Enhancing photostriction in KNN-based ceramics by constructing the morphotropic phase boundary and narrowing the energy band gap

Lead-free ferroelectric ceramics exhibiting photostriction effect has attracted a lot of attention in the past decade. Herein, we fabricated a series of (1?x)K_0.5Na_0.5NbO₃-x(La_0.51Na_0.49)(Zr_0.54Ni_0.46)O₃ ((1?x)KNN-xLNNZ) ceramics by traditional solid-state synthesis method aiming to improve photostriction. The addition of LNNZ in KNN has led to significant changes in phase structure and grain size. The ceramics with a composition of 0.97KNN-0.03LNNZ has shown a narrow bandgap ~2.43 eV, large piezoelectric coefficient (~209 pC/N), low dielectric loss (0.021 at 1 kHz) and high remnant polarization (~24 μC/cm²). Further, 0.97KNN-0.03LNNZ also exhibits a considerable photostrictive coefficient (~1.83 × 10^?9 m²W^?1), which is attributed to the combined effect of significantly narrow bandgap along with the morphotropic phase boundary. Further, all the substituted samples show distinct red shift of v1 mode compared to the pure KNN, which suggest a new kind of distortion introduced in (Nb, Zr, Ni)O₆ octahedron for KNN-based ceramics under variable power laser excitation. The obtained results indicate that LNNZ-substituted KNN ceramics can serve as a potential material for the fabrication of optomechanical devices.     

Preparation and characterization of (K0.5Na0.5)NbO3 ceramics

In this paper the preparation and characterization of the ceramic material (K_0.5Na_0.5)NbO₃ (KNN) has been studied. Although conventional processing of KNN is often reported to result in sintered bodies lacking sufficient density, samples produced in this work exhibit theoretical density over 95% and yield superior piezoelectric properties than those obtained by the same method and reported previously. The electromechanical coupling coefficient in the thickness direction, k_t, is found to reach 45%. Apart from k_t, the piezoelectric coefficients in longitudinal and planar directions (d₃₃ of 100pC/N and d₃₁ of 43pC/N), hysteresis loop, pyroelectric coefficient measurements and dielectric properties are presented.     

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.     

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.     

Piezoelectric and dielectric properties of (K0.44Na0.52Li0.04)(Nb0.86Ta0.10Sb0.04)O3–PVDF composites

(Li, Ta, Sb) modified sodium potassium niobate/poly(vinylidene fluoride) [(K_0.44Na_0.52Li_0.04)(Nb_0.86Ta_0.10Sb_0.04)O₃–PVDF] 0-3 composites were prepared by a cold press technique, and their piezoelectric and dielectric properties were characterized. All composites exhibited good dispersion of ceramic particles in the polymer matrix. The piezoelectric and dielectric constants were found to be enhanced as the concentration of sodium potassium niobate increases. Even though the process is simple, the composite prepared in this study showed better piezoelectric and dielectric properties than PZT–polymer composites. At room temperature, a (K_0.44Na_0.52Li_0.04)(Nb_0.86Ta_0.10Sb_0.04)O₃–PVDF (7:3) composite revealed a relative dielectric constant, ?_r = 166, piezoelectric constant, d₃₃ = 33 pC/N and coercive field, E_c = 5 kV/cm.     

Phase transformation mechanisms and piezoelectric properties of poly(vinylidene fluoride)/montmorillonite composite

Poly(vinylidene fluoride) (PVDF)/montmorillonite (MMT) composite with different MMT contents were prepared by solutions‐casting method. The effects of MMT on crystalline structure, morphology, dielectric property, piezoelectric property and phase transformation mechanism were studied. The results showed that acted as effective nucleation agents, the orientation of MMT were almost parallel to the surface of the film. The beta phase in the PVDF matrix was increased and the alpha phase was decreased. Relative dielectric constant and loss of the composite were increased with the increasing of MMT. The d₃₃ was also increased with MMT, which reached a maximum (5.8pC/N) with 2.0 wt % MMT. The mechanisms of changes in phase transformation and piezoelectric property were proposed based on experiment results. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012