氟聚合物压电驻极体的压电性及其电荷的动态行为

描述了一种可控微结构的多孔聚合物压电功能膜的制备方法,讨论了采用该工艺制备的聚四氟乙烯(PTFE)和全氟乙丙烯共聚物(FEP)复合膜压电驻极体的压电性能及其热稳定性.通过等温压电系数衰减和短路热刺激放电(TSD)方法,研究了氟聚合物复合膜压电活性热稳定性改善的根源,以及脱阱电荷输运和复合的特性.结果表明,这类氟聚合物压电驻极体膜的准静态压电系数d₃₃可高达2200pC/N;压电系数d₃₃的压强特性在直到20kPa的压强范围内呈现良好的 关键词： 氟聚合物 压电驻极体 热稳定性 电荷动态特性     

Improved piezoelectric properties of cellular polypropylene ferroelectrets by chemical modification

To improve the thermal stability of piezoelectricity of polypropylene (PP) ferroelectrets, chemical modification of the cellular PP film was performed via chromic acid oxidation and then hydrofluoric acid treatment. Deep chemical modification is achieved as indicated by the energy-dispersive X-ray analyses on the cross-section of the modified cellular PP film. The results of the isothermal decay for piezoelectric d ₃₃-coefficient at 70°C indicate the improved thermal stability of piezoelectricity and the enhanced piezoelectric activity of the modified PP ferroelectrets. The former is attributed to the improvement of thermal stability of the charges trapped in the internal void surface layers as indicated by the thermally stimulated discharge measurements, while the latter results not only from the improved thermal stability of the charges but also from the reduction in Young’s modulus of the PP ferroelectrets due to the chemical modification as revealed by the dielectric resonance analyses.     

人工调控微结构压电驻极体的热稳定性和电荷动态特性

利用表面带有周期性结构的硬质模板,通过冷压工艺将周期结构图案复制到多孔聚四氟乙烯(PTFE)薄膜表面,再经过热黏合工艺与致密氟化乙丙烯共聚物(FEP)薄膜复合,制备出了高度有序的微孔结构复合膜,并用电晕充电的方法对复合膜进行极化处理,最终获得氟聚合物复合膜压电驻极体.借助对这类复合膜压电驻极体介电谐振谱的测量,得到了材料的杨氏模量.并利用等温热老化工艺对它们的压电系数d33的热稳定性进行了考察.最后通过短路热刺激放电谱的测量和分析,讨论了该复合膜在热老化处理后的电荷动态 关键词： 有序结构 压电驻极体 压电性 电荷动态特性     

聚四氟乙烯和氟化乙丙烯共聚物复合膜的压电性

以多孔PTFE膜为骨架,而以致密（非多孔）FEP膜为储电介质层的孔洞结构复合压电驻极体膜的制备方法.利用正压电效应,测量了复合膜的准静态压电系数d₃₃;研究了压电系数的热稳定性和复合膜中空间电荷的动态特性;并通过介电谐振谱的分析,比较了这类复合膜的准静态和动态压电系数.结果表明：FEP和PTFE复合膜压电驻极体的准静态压电系数d₃₃可以达到300 pC/N.经90℃老化20 h 后的d₃₃仍保持在初 关键词： 压电驻极体 压电性 多孔聚四氟乙烯 致密氟化乙丙烯共聚物     

Piezoelectric coefficients of cross-linked polypropylene films stretched at elevated temperatures

Cross-linked polypropylene (XPP) foams are modified by a hot-stretching process and charged to be piezoelectric. The results show that a piezoelectric d₃₃ -coefficient of 308pC/N is obtained for sample with an elongation ratio of 200%. The dynamic d₃₃ value is smaller than the quasi-static value, which is probably due to the rise of Young’s modulus with increasing frequency. All the samples show pressure-independent d₃₃ in the range up to 30 kPa. Improved d₃₃ was obtained in the sample rough surface exposed to the corona during charging. Compared to linear PP, the stretched XPP shows pressure independence of d₃₃ in larger range.     

Pressure dependence of space charge deposition in piezoelectric polymer foams: simulations and experimental verification

The piezoelectric activity of PQ-50 cellular polypropylene (PP) foam (an example of a so-called ferroelectret) is measured after repeated charging in a nitrogen atmosphere at a range of pressures between 61 and 381?kPa. The results are compared against simulations using a multilayer electromechanical model based on Townsend??s model of Paschen breakdown and a realistic distribution of void heights determined from scanning electron micrographs. The modeled piezoelectric coefficients versus pressure are in good agreement with experimental data when adjusted Paschen coefficients are used, indicating that the Paschen curve for electric breakdown in gases needs to be modified for dielectric barrier discharges in microcavities. The highest d ₃₃ coefficients were achieved for pressures above 251?kPa. For previously uncharged PP foam, the model predicts an optimal charging pressure of 186 kPa.     

Evaluation of the piezoelectric behaviour produced by a thick-film transducer using digital speckle pattern interferometry

This paper presents an interferometric measurement of the out-of-plane deflections produced by a piezoelectric transducer, manufactured by thick-film deposition of a ceramic paste over an alumina substrate, when is subjected to a DC electric voltage. It is shown that a digital speckle pattern interferometer with an incorporated phase-shifting facility allows the measurement of nanometer displacements generated by the piezoelectric device. These measurements are used to evaluate the effective piezoelectric charge constant along the polarization direction (d₃₃)_eff that characterizes the thick-film transducer.     

Polarization and piezoelectricity in polymer films with artificial void structure

Laminated polymer-film systems with well-defined void structures were prepared from fluoroethylenepropylene (FEP) and polytetrafluoroethylene (PTFE) layers. First the PTFE films were patterned and then fusion-bonded with the FEP films. The laminates were subjected to either corona or contact charging in order to obtain the desired piezoelectricity. The build-up of the “macro-dipoles” in the laminated films was studied by recording the electric hysteresis loops. The resulting electro-mechanical properties were investigated by means of dielectric resonance spectroscopy (DRS) and direct measurements of the stress-strain relationship. Moreover, the thermal stability of the piezoelectric d ₃₃ coefficient was investigated at elevated temperatures and via thermally stimulated discharge (TSD) current measurements in short circuit. For 150 μm thick laminated films, consisting of one 25 μm thick PTFE layer, two 12.5 μm thick FEP layers, and a void of 100 μm height, the critical voltage necessary for the build-up of the “macro-dipoles” in the inner voids was approximately 1400 V, which agrees with the value calculated from the Paschen Law. A quasi-static piezoelectric d ₃₃ coefficient up to 300 pC/N was observed after corona charging. The mechanical properties of the film systems are highly anisotropic. At room temperature, the Young’s moduli of the laminated film system are around 0.37 MPa in the thickness direction and 274 MPa in the lateral direction, respectively. Using these values, the theoretical shape anisotropy ratio of the void was calculated, which agrees well with experimental observation. Compared with films that do not exhibit structural regularity, the laminates showed improved thermal stability of the d ₃₃ coefficients. The thermal stability of d ₃₃ can be further improved by pre-aging. E.g., the reduction of the d ₃₃ value in the sample pre-aged at 150°C for 5 h was less than 5% after annealing for 30 h at a temperature of 90°C.     

Polytetrafluoroethylene piezoelectrets prepared by sintering process

Polytetrafluoroethylene (PTFE) films with a void structure are prepared by a sintering process. Such void PTFE films are piezoelectric after proper corona charging. The quasi-static piezoelectric d ₃₃ coefficients up to 250 pC/N are achieved for the samples which were made of compact and biaxial-tension porous PTFE layers. Pre-ageing treatment is an effective method to further improve the thermal stability. For the samples with pre-ageing treatment, the reduction of the d ₃₃ coefficients is around 2% per day when exposed to 120 °C.     

Effect of carbon black on properties of 0–3 piezoelectric ceramic/cement composites

0–3 cement-based piezoelectric composites were fabricated using sulphoaluminate cement and piezoelectric ceramic [0.08Pb(Li_1/4Nb_3/4)O₃ · 0.47PbTiO₃ · 0.45PbZrO₃] [P(LN)ZT] as raw materials by compressing technique. The influences of carbon black content on the piezoelectric and dielectric properties, electric conductivity and impedance were investigated. The results indicate that the piezoelectric strain constant d₃₃ and piezoelectric voltage constant g₃₃ of the composites increase gradually with a suitable carbon black addition. When the carbon black content is 0.3 wt%, both of the piezoelectric strain constant d₃₃ and piezoelectric voltage constant g₃₃ of the composite exist the maximum value, which are 17.45 pC N⁻¹ and 36.3 mV m N⁻¹, respectively. As the carbon black content increases, the dielectric constant ε_r, dielectric loss tanδ and electric conductivity σ of the composites all increase, while the impedance decreases. In the frequency range tested, the more the carbon black content, the higher the ε_r value. The planar electromechanical coupling coefficient K_p, the thickness electromechanical coupling coefficient K_t and the mechanical quality factor Q_m are almost unaffected by the carbon black content.     

PbZrO3-PbTiO3系压电陶瓷极化效应的正电子湮没研究

用正电子寿命测量方法研究了锆钛酸铅(简称PZT)压电陶瓷的电场极化效应。发现正电子平均寿命τ_m随极化场强E的提高而增大。讨论了τ_m增大的微观机制,这可能主要归因于内电场增大在能量上有利于正电子形成qPs态。同时进行了介电常数、机电耦合系数、压电常数等的测量,并与正电子寿命测量的结果作了对比,认为将正电子作为测量电畴转向程度及电子能量状态变化的一种手段是可能的。正电子寿命测量采用了特殊的单样品法,并就与此有关的数据处理和分析方法进行了若干讨论。 关键词：     

Piezoelectric properties of non-uniform polymeric structures under static load

ABSTRACT

Piezo-electrical properties of structures containing ‘soft’ and ‘hard’ dielectric layers with charge stored on the interfaces are described in the paper. The piezo-activation process of structures containing layers with gas voids by partial discharges is described. The influence of the mechanical properties of the ‘soft’ layer on the piezoelectric parameter d₃₃ value and its dependence on the static pressure p are also discussed. It was found experimentally, that for the fibrous type of ‘soft’ dielectric layer, the dependence of the piezoelectric parameter d₃₃ (p) can be described by the function d₃₃ ÷ p^?n, where n ≤ 1.     

Physical foaming of fluorinated ethylene-propylene (FEP) copolymers in supercritical carbon dioxide: single-film fluoropolymer piezoelectrets

Cellular polymer foams with significant piezoelectric activity were prepared from fluorinated ethylene-propylene (FEP) copolymers. The required void structure is obtained by saturation of FEP films with supercritical carbon dioxide and a subsequent heat treatment for controlled inflation. After bipolar electric charging of the voids and evaporation of electrodes, the FEP films show piezoelectric d₃₃ coefficients up to 50 pC/N. The present physical foaming process generates cellular fluoropolymer piezoelectret films with usually only one single void across the film thickness. PACS 81.05.Rm; 77.65.-j; 77.84.Jd; 61.41.+e     

Nonlinear properties of barium titanate in the electric field range 0≤<Emphasis Type="Italic">E</Emphasis>≤5.5×0<Superscript>7</Superscript> V/m

X-ray structural studies and dielectric measurements of BaTiO₃ single crystals were performed in the dc electric field range 0≤E≤5.5×10⁷ V/m. The field dependence of the tetragonal cell parameter obtained was used to calculate the field dependence of the piezoelectric modulus d₃₃. The piezoelectric modulus d₃₃ and the dielectric permittivity vary in magnitude by a factor of two with the field varied in the above range. The observed nonlinear behavior is shown to fit well to a relation connecting the dielectric with the electromechanical characteristics of the crystal.     

Theoretical investigation of the intrinsic piezoelectric properties for tetragonal BaTiO3 epitaxial films

The orientation dependences of the converse longitudinal piezoelectric constant d_33,f, and the in-plane converse piezoelectric constant e_31,f, are calculated for tetragonal barium titanate epitaxial films. The calculations demonstrate that both e_31,f and d_33,f have their maximum values along an axis close to the (1 1 1) direction of the pseudo-cubic system, which are similar to the orientation dependence results for a tetragonal BaTiO₃ single crystal. The calculated piezoelectric constants for a (1 1 1) oriented BaTiO₃ epitaxial film (e_31,f = −23 C/m², d_33,f = 124 pm/V) suggest that it is a good candidate material for lead-free MEMS applications.     

有序结构氟聚合物压电驻极体的制备和压电性研究

描述了一种有序微孔结构压电聚合物功能膜的制备方法,利用模板的高度有序实现薄膜微孔结构的精确控制.将此制备方法用于氟聚合物压电驻极体薄膜的制备,通过扫描电子显微镜(SEM)对其微观结构的观察表明薄膜具有理想的有序结构.对氟聚合物压电驻极体压电性的研究则是利用正压电效应测量准静态压电系数d₃₃,通过等温衰减和压强依赖性的测量考察其压电性能.结果表明:有序结构氟聚合物压电驻极体的准静态压电系数d₃₃可高达300 pC/N;与无序结构氟聚合物     

Relationship between phase structure and electrical properties of (K0.5Na0.5)NbO3-LiTaO3 lead-free ceramics

Lead-free piezoelectric ceramics of (1−x)K_0.5Na_0.5NbO₃-xLiTaO₃ (KNN-LT) system have been investigated in this work. X-ray diffraction, Raman spectra measurements, DSC (Differential Scanning Calorimetric), and dielectric constant versus temperature provide direct evidence that the phase transition temperature between tetragonal and orthorhombic shift to lower temperature with the increasing of LT content. The KNN-0.05LT ceramics exhibit the highest high-field d₃₃ up to 220 pm/V. At the same time, we also investigated the relationship between phase structure and electric properties, showing that the orthorhombic phase presents better piezoelectric temperature stabilities than the tetragonal phase. The result may provide a new way for KNN-based lead-free ceramics.     

Thermally stable fluorocarbon ferroelectrets with high piezoelectric coefficient

Fused layers of polytetrafluoroethylene (PTFE) and fluoroethylenepropylene (FEP) films with small interfacial cellular gas voids show large quasistatic piezoelectric d₃₃-coefficients of more than 1000 pC/N. After annealing at a temperature of 90 °C for 4 days, d₃₃ amounts to about 400 pC/N and thereafter changes by less than 10 percent over a period of 5 days at this temperature. The piezoelectric coefficient is independent of applied pressure in the range up to 20 kPa. Its frequency response shows a small decrease up to the vicinity of the thickness resonance frequency at 40 to 150 kHz. PACS 77.65.Bn; 77.55.+f; 77.84.Jd     

孔隙率及晶粒尺寸对多孔PZT陶瓷介电和压电性能的影响及机理研究

采用添加造孔剂的方法制备多孔锆钛酸铅(PZT)陶瓷，并研究了孔隙率和晶粒尺寸对多孔PZT陶瓷介电和压电性能的影响及机理.研究表明：孔隙率的增加降低了多孔PZT陶瓷的介电常数，提高了静水压优值，并证明在一定条件下孔隙率与介电常数关系可由Okazaki经验公式及Banno模型预测；晶粒尺寸增加，多孔PZT陶瓷的介电常数、压电系数和优值增加，并可用Okazaki空间电荷理论解释晶粒尺寸对试样介电和压电性能的影响.对于添加重量百分数为10%造孔剂的多孔PZT陶瓷，当烧结温度为1300℃时，孔隙率为34%，d关键词： 多孔PZT陶瓷 静水压优值 压电性能 介电性能     

Non-interferometric transient quantitative phase microscopy for ultrafast engineering

Lead-free piezoelectric ceramics Bi_0.5(Na_1-x-yK_xAg_y)_0.5TiO₃ [BNKAT(x/y)] have been synthesized by the mixed oxide method. The effects of the amount of K⁺ and Ag⁺ on the electrical properties were examined. X-ray diffraction patterns indicate that K⁺ and Ag⁺ ions partially substitute for the Na⁺ ions in Bi_0.5Na_0.5TiO₃ and form a solid solution during sintering. At room temperature, the ceramics exhibit good performances with piezoelectric constant d₃₃=189 pC/N, electromechanical coupling factor k_p=35.0%, remanent polarization P_r=39.5 μC/cm², and coercive field E_c=3.3 kV/mm, respectively. The curves of the dielectric constant ε_r and loss tangent tan δ versus temperature show that the transition temperature from ferroelectric to anti-ferroelectric phase decreases with increasing the K⁺ content for the compositions researched. The dependencies of k_p and polarization versus electric (P–E) hysteresis loops on temperature reveal that the depolarization temperature T_d of BNKAT(0.15/0.015) ceramics, which have good piezoelectric properties (d₃₃=134 pC/N, k_p=32.5%) and strong ferroelectricity (P_r=39.5 μC/cm², E_c=4.1 kV/mm) at room temperature, is above 160 °C. PACS 77.22.-d; 77.65.Bn; 77.80.Bh; 77.80.Dj; 77.84.Dy