Piezoelectricity of single- and multi-layer cellular polypropylene film electrets

The piezoelectricity of a pressure-treated cellular polypropylene (PP) (commercially available, trade name PQ50) film electret was studied by the measurement of direct- and inverse-piezoelectric d₃₃ coefficient. The sample expanded with optimal parameters has a quasi-static piezoelectric d₃₃ coefficient of more than 600 pC/N, which is about 40 times as high as that of polyvinylidene fluoride (PVDF). In addition, the hybrid multi-layer system, which properly combines single-layer cellular PP film electrets, shows a quasi-static piezoelectric sensitivity of as high as 2010 pC/N. This is around three times higher than that of well-known lead zirconate titanate (PZT) ceramics. The results are theoretically and technically helpful to promote the application of cellular PP film electrets.     

单层及多层PP蜂窝膜驻极体的压电性

经压力膨化处理后,以正逆压电系数d33测量研究了一种经无栅电晕充电的国产商用聚丙烯蜂窝膜(cellular PP,商品名PQ50)驻极体的压电性.经过优化工艺参数压力膨化处理后的PQ50蜂窝膜呈现600pC/N以上的准静态压电系数,这一量值约为PVDF相关系数的40倍.而通过将单层PQ50蜂窝膜驻极体粘贴形成合理的多层结构,得到的复合膜系压电系数d33高达2010pC/N,约为PZT压电陶瓷相应系数的3倍.从而为拓宽这类新一代的非极性孔洞聚合物压电功能膜应用领域,推动其应用进程提供了一定的理论和技术依据.     

Quasi-static and dynamic piezoelectric <Emphasis Type="Italic">d</Emphasis><Subscript>33</Subscript> coefficients of irradiation cross-linked polypropylene ferroelectrets

Irradiation cross-linked polypropylene (IXPP) foams show high piezoelectric activity after proper hot-pressing treatment and corona charging. Quasi-static piezoelectric d ₃₃ coefficients around 400 pC/N were measured by means of the direct piezoelectric effect. Dynamic values of the inverse piezoelectric d ₃₃ coefficients, determined from the dielectric resonance spectra at 220 kHz, is about 68% of the quasi-static d ₃₃ values. The difference between the quasi-static and the dynamic values of d ₃₃ is probably due to the enhancement of Young’s modulus of IXPP with increasing frequency. The piezoelectric d ₃₃ coefficients are slightly dependent on the applied pressure in the range up to 50 kPa. The d ₃₃-values decrease by 70% when the samples are exposed to 90 °C for 1 day; and a pre-aging treatment improves the thermal stability of the d ₃₃ coefficients.     

Characterization of piezoelectric films of foamed polyethylene obtained by extrusion

Foamed polyethylene (MDPE) films obtained by extrusion have been characterized by X-ray diffraction, thermogravimetric analysis and tensile tests. The piezoelectric properties have been determined by calculation of piezoelectric constant d₃₃, thermally stimulated depolarized current method and calculation of activation energy depolarization of electrets. It has been found that the crystallinity and internal morphology, including cellular structure, affect the possibility of an effective polarization in order to obtain a piezoelectric material from foamed MDPE. The conditions of processing have a great influence on the piezoelectric properties. The value of piezoelectric constant attains ~18 pC/N and ~75 pC/N for low stress range and diminishes for higher stresses, temperature T_m?~?72 °C and ~82 °C, approximate activation energy attains 2.67 and 3.28 eV, for compacted and non-compacted film, respectively. Because of the simple and cheap method of foaming PE films of piezoelectric properties it is worthy to take care regarding their application for pressure sensors.     

Phase diagram and electric properties of the (Mn, K)-modified Bi0.5Na0.5TiO3–BaTiO3 lead-free ceramics

In this study, the phase diagram and electric properties were demonstrated for a (Mn, K)-modified Bi_0.5Na_0.5TiO₃ (BNT)-based solid solution. (0.935−x) Bi_0.5Na_0.5TiO₃−xBi_0.5K_0.5TiO₃−0.065BaTiO₃ with 0.5% mol Mn doping was prepared by a conventional solid-state reaction method. A morphotropic phase boundary (MPB) formed between the ferroelectric rhombohedral and tetragonal phases around x of 0.04 with the MPB tolerance factor t of 0.984–0.986. The temperature and composition dependence of the dielectric, piezoelectric, ferroelectric properties along with the strain characteristics were investigated in detail and a phase diagram was presented. Around the MPB region, the maximum values of piezoelectric constant d₃₃^* d_{33}^{*} of 290 pC/N, d ₃₃ of 155 pC/N, dielectric constant e₃₃^T /e₀ \varepsilon_{33}^{T} /\varepsilon_{0} of 1059 and low dielectric loss tangent tan δ of 0.017 were obtained. In addition, the authors also suggest that the solid solution with composition x of 0.24, exhibiting both high-depolarization temperature T _d of 182 °C, d₃₃^* d_{33}^{*} of 156 pC/N, d ₃₃ of 130 pC/N, will be favorable for high-temperature actuator and sensor applications.     

Performance enhancements in poly(vinylidene fluoride)-based piezoelectric films prepared by the extrusion-casting process

The extrusion-casting process can realize large-area and continuous preparation of polymer-based films. In this paper, five different types of polyvinylidene fluoride (PVDF)-based piezoelectric films: PVDF, PVDF/PZT, PVDF/PZT@105, PVDF/PZT/BNNS and PVDF/PZT@105/BNNS were prepared by the extrusion-casting process. The mechanical, dielectric, thermal conductivity and piezoelectric properties were studied. It is found that PZT particles can well improve the dielectric performance and also the mechanical stability under variable temperature conditions. PZT powders modified by titanate coupling reagent (UP-105) can further improve the performance of the PVDF/PZT@105 films by improving the combination and dispersion of organic and inorganic phases. The addition of boron nitride nanosheets (BNNS) can improve the thermal conductivity of the films and the breakdown strength. The piezoelectric coefficient (d₃₃) of PVDF/PZT@105/BNNS composite film can reach 21pC/N, compared with the neat PVDF film (4pC/N) and PZT/PVDF (9pC/N) film realizing great improvement.

     

Poling field versus piezoelectric property for [001]<Subscript><Emphasis Type="Italic">c</Emphasis></Subscript> oriented 91%Pb(Zn<Subscript>1/3</Subscript>Nb<Subscript>2/3</Subscript>)O<Subscript>3</Subscript>–9%PbTiO<Subscript>3</Subscript> single crystals

Electromechanical property measurements and microstructure observations using optical microscopy were performed on a [001] _c oriented k ₃₃ resonator made of 91%Pb(Zn_1/3Nb_2/3)O₃–9%PbTiO₃ single crystal, which was polarized under different electric fields. At room temperature, when the poling field is 1100 V/mm, the electromechanical coupling factor k ₃₃ is 0.90 and piezoelectric coefficient d ₃₃ is 1665 pC/N. Such superior electromechanical properties could be attributed to the formation of monoclinic multi-domain structure, which transforms to tetragonal phase at 46 °C. While at a higher poling field of 1200 V/mm, the crystal becomes single-domain tetragonal state and its k ₃₃ and d ₃₃ are only about 0.69 and 850 pC/N, respectively. The critical poling field to transform the monoclinic phase to the tetragonal phase is found to be ~1120 V/mm.     

聚丙烯孔洞驻极体薄膜的突出压电活性及其应用研究

聚丙烯(PP)孔洞膜可呈现高达1000pC/N的准静态压电d33系数,是久负盛名的铁电聚合物PVDF相应系数的50倍以上,可和压电陶瓷相媲美.基于国内外最新研究成果,综述了PP孔洞膜的制备技术、极化方法、压电活性以及可能的应用前景.     

Densification of (Na,K)NbO<Subscript>3</Subscript> piezoelectric ceramics by two-step mixing process

Lead-free Na_0.5K_0.5NbO₃ (NKN) piezoelectric ceramics were sintered with a new process, “two-step mixing process,” in which a part of alkali source powders was initially preserved and mixed with the rest matrix powders after the calcinations step. As a result, the sintering of NKN ceramics was improved, and the sample sintered at 1082 °C with the initial preservation ratio (R _A) of 5% demonstrated the highest density of ρ = 4.38 g/cm³ (97.1% of the theoretical density), compared with ρ = 4.36 g/cm³ (96.7% of the theoretical density) for the non-preservation specimen (R _A = 0%). The former sample showed the best piezoelectric constant of d ₃₃ = 125 pC/N and electromechanical coupling coefficient of k _p = 0.42, while the latter sample had d ₃₃ = 116 pC/N and k _p = 0.37. These results indicated that the two-step mixing process was effective for the sintering of lead-free NKN ceramics, despite no sintering additive and cold isostatic pressing were used.     

Large strain response in acceptor- and donor-doped Bi<Subscript>0.5</Subscript>Na<Subscript>0.5</Subscript>TiO<Subscript>3</Subscript>-based lead-free ceramics

Effects of Fe and La addition on the dielectric, ferroelectric, and piezoelectric properties of Bi_0.5Na_0.5TiO₃–Bi_0.5Li_0.5TiO₃–BaTiO₃–Mn ceramics were investigated. Similar to the doping effect in lead-based piezoelectric materials, here the Fe-doped ceramic created a hard effect with an improved mechanical quality factor (Q _m) ~ 160, coercive field (E _c) ~ 2.9 kV/mm, decreased dielectric constant ( e₃₃^T /e₀ ) ~ 80 3, \left( {\varepsilon_{33}^{T} /\varepsilon_{0} } \right)\sim 80 3, and loss (tanδ) ~ 0.024 while the La-doped one indicated a soft feature with improved piezoelectric constant (d ₃₃) ~ 184 pC/N, e₃₃^T /e₀   ~ 983, \varepsilon_{33}^{T} /\varepsilon_{0} \,\sim { 983}, tanδ ~ 0.033, and decreased E _c ~ 2.46 kV/mm. In addition, the temperature dependence of the ferroelectric hysteresis loops and strain response under unipolar electric field was also studied. Around the depolarization temperature T _d, large strain value was obtained with the normalized d₃₃^* d_{33}^{*} up to ~1,000 pC/N, which was suggested originated from the development of the short-range order or non-polar phases in the ferroelectric matrix. All these would provide a new way to realize high piezoelectric response for practical application in different temperature scale.     

The effect of processing conditions on the morphology, thermomechanical, dielectric, and piezoelectric properties of P(VDF-TrFE)/BaTiO3 composites

In this study (0–3) P(VDF-TrFE)/BaTiO₃ composites containing up to 60 vol% of ceramic phase were prepared by solvent casting or compression molding. Their thermomechanical, dielectric, and piezoelectric properties were investigated, and discussed in the light of the properties of the basic components, the processing route and the resulting morphology. The crystalline structure of the P(VDF-TrFE) matrix was found to be highly dependent on the processing route, while the structure of BaTiO₃ was not affected by any of the processing steps. The mechanical properties of the solvent cast materials showed a maximum at 30 vol% BaTiO₃, while they increased monotonically with BaTiO₃ content for compression molded materials. This difference was attributed to a higher amount of porosity and inhomogeneities in the solvent cast composites. Permittivity as high as 120 and piezoelectric coefficient d ₃₃ up to 32 pC/N were obtained for compression molded composites, and the observed decrease in d ₃₃ with aging time was attributed to the effect of mechanical stress release in the polymer matrix.     

Microstructure,electrical properties of CeO<Subscript>2</Subscript>-doped (K<Subscript>0.5</Subscript>Na<Subscript>0.5</Subscript>)NbO<Subscript>3</Subscript> lead-free piezoelectric ceramics

CeO₂-doped K_0.5Na_0.5NbO₃ lead-free piezoelectric ceramics have been fabricated by a conventional ceramic fabrication technique. The ceramics retain the orthorhombic perovskite structure at low doping levels (<1 mol.%). Our results also demonstrate that the Ce-doping can suppress the grain growth, promote the densification, decrease the ferroelectric–paraelectric phase transition temperature (T _C), and improve the dielectric and piezoelectric properties. For the ceramic doped with 0.75 mol.% CeO₂, the dielectric and piezoelectric properties become optimum: piezoelectric coefficient d ₃₃ = 130 pC/N, planar electromechanical coupling coefficient k _p = 0.38, relative permittivity ε_r = 820, and loss tangent tanδ = 3%.     

Microstructure and electrical properties of (Na<Subscript>1.015−x</Subscript>K<Subscript>x</Subscript>)NbO<Subscript>3</Subscript> lead-free piezoceramics

In order to obtain the morphotropic phase boundary (MPB) and good piezoelectric properties, lead-free (Na_1.015−xK_x)NbO₃ (x = 0.32–0.35) piezoceramics were synthesized by conventional solid state sintering. The x-ray diffraction results show that the lattice parameters of the monoclinic primitive cell peak at x = 0.34. The scanning electron microscopy and energy dispersive spectroscopy reveal that the excess sodium may be an important reason for the abnormal growth of the grains larger than 20 μm. All the samples exhibit double-like hysteresis loops and it may also be attributed to the excess Na⁺. Although the salient microstructure was found in the studied range, the piezoelectric and ferroelectric properties changed slightly with increasing x from 0.32 to 0.35. The values of piezoelectric coefficient d ₃₃ obtained in this study are as high as about 75 pC/N which is close to that of normally prepared (Na_0.5K_0.5)NbO₃ ceramics with MPB structure.     

Influence of sintering temperature on piezoelectric properties of (K0.4425Na0.52Li0.0375)(Nb0.8925Sb0.07Ta0.0375)O3 lead-free piezoelectric ceramics

Microstructure characteristics, phase transition, and electrical properties of (K_0.4425Na_0.52Li_0.0375) (Nb_0.8925Sb_0.07Ta_0.0375)O₃ (KNLNST) lead-free piezoelectric ceramics prepared by normal sintering were investigated with an emphasis on the influence of sintering temperature. The microstructure and piezoelectric, ferroelectric, and dielectric properties were investigated, with a special emphasis on the influence of sintering temperature from 1,100 to 1,140 °C. Orthorhombic phases mainly exist in the ceramics sintered at 1,100–1,130 °C, whereas the tetragonal phase becomes dominant when sintering temperature is above 1,130 °C. Because of the existence of MPB-like transitional behavior, the piezoelectric coefficient (d ₃₃), electromechanical coupling coefficient (kp), and dielectric constant (ε) show peak values of 304pC/N, 0.48, and 1,909, respectively, which are obtained in the sample sintered at 1,120 °C, and its Curie temperature (T _C) is about 271 °C.     

Crystal structure and properties of BaTiO<Subscript>3</Subscript>–(Bi<Subscript>0.5</Subscript>Na<Subscript>0.5</Subscript>)TiO<Subscript>3</Subscript> ceramic system

(1 − x)BaTiO₃–x(Bi_0.5Na_0.5)TiO₃ (x ranged from 0.01 to 0.96) ceramics were fabricated by the conventional ceramic technique. The crystal structure, as well as dielectric and piezoelectric properties of the ceramics were studied. All the ceramics formed single-phase solid solutions with perovskite structure after sintering in air at 1150–1250 °C for 2–4 h. The crystal structure and microstructure varied gradually with the increase of (Bi_0.5Na_0.5)TiO₃ (BNT) content. The Curie temperature, T _c, shifted monotonously to high temperature as BNT increased. The ceramics with 20–90 mol% BNT had relatively low and stable dielectric loss characteristics. The piezoelectric constant, d ₃₃, enhanced with the increase of BNT content through a maximum value in a composition of 93 mol% BNT and then tended to decrease. The maximum value, 148 pC/N, of piezoelectric constant d ₃₃ together with the electromechanical coupling factors, k _t, 19.8% and k _p, 15.8%, were obtained when BNT was 93 mol%.     

The effects of CuO-doping on dielectric and piezoelectric properties of Bi<Subscript>0.5</Subscript>Na<Subscript>0.5</Subscript>TiO<Subscript>3</Subscript>–Ba(Zr,Ti)O<Subscript>3</Subscript> lead-free ceramics

CuO-doped lead-free ceramics based on bismuth sodium titanate (Bi_0.5Na_0.5TiO₃, BNT) and barium zirconate titanate (Ba(Zr_0.07Ti_0.93)O₃, BZT) were prepared via a multi-step solid-state reaction process. The BNT–BZT with CuO dopant ceramics sintered at 1150–1180 °C for 2 h in air showed a pure perovskite structure. SEM images reveal that a small amount of CuO (<2 mol%) play a significant role on the microstructure to improve its sintering attributes, while it will degrade when the dopant is added beyond 2 mol%. The dielectric and piezoelectric properties of CuO-doped BNT–BZT ceramics were evaluated. At room temperature, the sample doped with 2 mol% CuO shows quite good properties such as a high piezoelectric constant (d ₃₃ ∼156.5 pC/N) and a high electromechanical coupling factor (k _t ∼52%). The depolarization temperature increased dramatically and the maximum permittivity temperature decreased slightly.     

A new binderless thick-film piezoelectric paste

This paper presents an investigation into a screen printable piezoelectric paste formulated from a blend of PZT-Pz29 powders of different mean particle size mixed in an organic vehicle. In order to enhance d₃₃ properties of the thick-film (a piezoelectric coefficient), no binder material was mixed into the paste. The d₃₃ coefficient and maximum applied electrical field of devices processed at peak temperatures of 150, 200, 750, 850 and 1,000°C were measured and the film adhesion assessed using scratch and tape tests. The applications that would benefit from these enhanced properties are also discussed. The thick-films produced at these processing temperatures showed good adhesion to 96% alumina substrates. They also showed the ability to withstand high electrical fields and a significant enhancement in d₃₃ when compared to thick-film materials processed at similar temperatures using polymer or glass binders. A maximum average d₃₃ value of 168pCN⁻¹ was obtained for samples processed at a peak temperature of 1,000°C. This is 28% higher than the reported d₃₃ value for a conventional piezoelectric thick-film processed at the same temperature. All samples withstood electric field strengths of over 14 MVm⁻¹ which is between 2.5 and 4.5 times higher than that used for conventional piezoelectric thick-films.     

Effect of ZnO on the microstructure and electrical properties of (K<Subscript>0.5</Subscript>Na<Subscript>0.5</Subscript>)NbO<Subscript>3</Subscript> lead-free piezoelectric ceramics

K_0.5Na_0.5NbO₃–x ZnO (KNN–xZn) lead-free ceramics have been prepared using the conventional sintering technique and the effects of ZnO addition on the phase structure and piezoelectric properties of the ceramics have been studied. Our results reveal that a small amount of ZnO can improve the density of the ceramics effectively. Because of the high density and ZnO doping effects, the piezoelectric and dielectric properties of the ceramics are improved considerably. The good piezoelectric and dielectric properties of d ₃₃ = 114 pC/N, k _p = 0.36, ε _r = 395, and Q _m = 68 were obtained for the KNN ceramics doped with 1 mol% ZnO. Therefore, the KNN-1.0 mol%Zn ceramics is a good candidate for lead-free piezoelectric application.     

Piezoelectric properties of [Bi<Subscript>0.5</Subscript>(Na<Subscript>0.7</Subscript>K<Subscript>0.25</Subscript>Li<Subscript>0.05</Subscript>)<Subscript>0.5</Subscript>]TiO<Subscript>3</Subscript>−Ba(Ti,Zr)O<Subscript>3</Subscript> binary system ceramics

Dense lead-free binary system piezoelectric ceramics (1 − x)[Bi_0.5(Na_0.7K_0.25Li_0.05)_0.5]TiO₃−xBa(Ti_0.95Zr_0.05)O₃ (BNKLT–BZT) were prepared by a two-step sintering process. A phase transition from rhombohedral to tetragonal was observed with increasing BZT fraction in the range x = 0.06–0.1 and the morphotropic phase boundary (MPB) between rhombohedral and tetragonal appears in this range. Ceramics containing 10 mol% BZT with tetragonal phase near the MPB region has the maximum piezoelectric constant d ₃₃(151pC/N).     

Electrical properties of manganese modified sodium potassium lithium niobate lead-free piezoelectric ceramics

Effects of MnO₂ doping on the microstructure, densification, dielectric, ferroelectric and piezoelectric properties of (Na_0.5K_0.5)_0.935Li_0.065NbO₃ (NKLN) lead-free piezoelectric ceramics were investigated. On the one hand, the addition of a small amount of MnO₂ has little effect on the crystalline structure, however, slightly promotes sintering and grain growth, and improves the uniformity of microstructure to a certain degree. On the other hand, MnO₂ doped NKLN ceramics show hard properties in piezoelectric activities, possessing decreased room-temperature dielectric constant, loss tangent and piezoelectric constants d ₃₃, and increased mechanical quality factors Q _m. The 1.2 mol% MnO₂ doped NKLN ceramics have a loss tangent of approximately 1%, a Q _m of ∼170 and a d ₃₃ of 150 pC/N. These effects were considered to come from the formation of oxygen vacancies and the multi-valence states of Mn ions.