Electric field-induced strain behavior in lithium- and copper-added potassium sodium niobate piezoceramics and 1-3 piezocomposites

Potassium sodium niobate (KNN)-based leadfree materials were prepared and their field-induced strain behaviors were investigated. Ceramic lead-free piezoelectric materials were prepared in bulk and fiber forms with 1 mol% CuO-added potassium sodium niobate K0.5Na0.5NbO3 and x = 7 mol% lithium-modified (K(0.5-x/2)Na(0.5-x/2)Li(x))NbO(3) compositions. Fibers were drawn using a novel alginate gelation technique. Piezocomposites were prepared from these fibers with 1-3 connectivity and an epoxy matrix. A fully recoverable electrostrain of up to approximately 0.11% was observed in the CuO-added sample, whereas the Li-modified sample yielded up to 0.10% at 50 kV/cm electric field. A strain value of up to approximately 0.03% at 50 kV/cm electric field was obtained for piezocomposites prepared from lithium-modified fibers. The high-field converse piezoelectric coefficient was calculated from the strain-electric field (x-E) graph for all samples. Strain characteristics of the bulk and piezocomposite samples were analyzed based on the variation of strain with respect to square of the polarization (x-P2) to determine the electrostrictive contribution to the strain.     

Nonlinear electric-mechanical behavior of a soft PZT-51 ferroelectric ceramic

In this investigation, the electric-mechanical response of a PZT ferroelectric ceramic subjected to the combined electric-mechanical loads was experimentally observed. The effect of different compressive stress levels on the electromechanical response was examined. The stress-strain relationship was also measured. The ceramic sample was isolated from the test frame and the high voltage arcing were prevented effectively in the setup which promotes the precise measurement and makes the systemic experimental results available. With a high voltage amplifier and a servo-hydraulic test frame, the butterfly shaped strain vs. electric field curves and the electric displacement vs. electric field hysteresis loops of a soft PZT ceramic at different compressive stress levels were measured. The results show that the electric-mechanical coupled properties of the PZT ceramic are the function of the compressive stress. The switching criteria are given to account for the experimental results and to analyze the nonlinear electric-mechanical behavior relative to the domain switching process in this paper.     

发射型PZT压电陶瓷的应变及性能

测量了几种发射型 PZT 压电陶瓷的电场应变曲线和电滞回线,探讨了它们与性能间的关系。认为 PZT陶瓷的应变量是一个与剩余极化量同样重要的用来衡量材料压电性能的基本参数。PZT 压电陶瓷的应变由两部分组成:低场强下的应变由畴的转向形成,高场强下的应变则是以畴伸缩产生的应变为主。单位场强的畴伸缩应变量与准静态压电系数 d_(33)值相当。     

Dielectric properties of lead zirconate titanate thin films seeded with barium strontium titanate nanoparticles

A low temperature synthetic method recently proposed by the authors was applied to the fabrication of lead zirconate titanate (PZT) thin films containing crystalline seeds of barium strontium titanate (BST) nanoparticles. PZT precursor and the BST particles were prepared with complex alkoxide methods. Precursor solution suspending the BST particles was spin-coated on Pt/Ti/SiO₂/Si substrate to film thickness of 500–800 nm at particle concentrations of 0–25.1 mol%, and annealed at various temperatures. Seeding of BST particles prevented the formation of pyrochlore phases, which appeared at temperatures above 400 °C in unseeded PZT films, and induced crystallization of PZT into perovskite structures at 420 °C, which was more than 100 °C below the crystallization temperature of the unseeded PZT films. Measurement of dielectric properties at 1 kHz showed that the 25.1 mol% BST-seeded PZT films annealed at 450 °C had a dielectric constant as high as 300 with a dissipation factor of 0.05. Leakage current density of the film was less than 1×10⁻⁶ A/cm² at applied electric field from 0 to 64 kV/cm.     

Dielectric and field-induced strain behaviour of (Pb1−xBax) ZrO3 ceramics

The effects of Ba2+ substitution on the dielectric properties and induced strain behaviour of the (Pb1–xBax) ZrO3 ceramics (0.05x0.3) have been investigated as a function of x. A new phase diagram of the (Pb1–xBax) ZrO3 system, indicating the field effect on the phase transition, is also presented. As the Ba2+ content increases, the Curie temperature decreases linearly, whereas maximum dielectric constant increases for up to 20 mol% Ba2+ addition, and then decreases with further Ba2+ addition. Based on the hysteresis loops, the temperature range of the ferroelectric phase as an intermediate phase between the antiferroelectric and paraelectric phases, increases with increasing electric field and Ba2+ content. The ferroelectric loops are induced at room temperature for the specimens containing above 10 mol% Ba2+ by applying an electric field up to 25 kV cm–1. However, for the 5 mol% Ba2+-substituted specimen, no ferroelectric loop is induced, even with applied fields up to 55 kV cm–1. The phase transition due to electric field and Ba2+ addition is also confirmed by the measurement of the field-induced longitudinal strain.     

Effect of external electric field on the grain growth of barium titanate in N2 atmosphere

The effect of dc electric field upon the spatial variation of microstructure during the sintering of BaTiO₃ in a N₂ atmosphere was investigated. When BaTiO₃ specimens were heat-treated in a N₂ atmosphere at 1350 °C under an electric field, grain growth was enhanced at the positive-biased region for a 0.5 mol% Nb-doped specimen, while it was promoted at the negative-biased region for a 3.0 mol% Nb-doped specimen. The grain growth behavior at both the positive and negative-biased region was similar for a 1.0 mol% Nb-doped specimen. The results have been explained mainly in terms of the boundary potential, which varies with the donor concentration, and the oxygen partial pressure of the surrounding atmosphere.     

铁电陶瓷的电畴及畴变观测研究进展

铁电陶瓷材料，特别是锆钛酸铅(PZT)在众多领域具有广泛的应用前景，影响其推广应用的主要因素是使用过程中外电、力场引起的材料性能的退化。观测铁电电畴及畴变的方法对研究其在外场下性能破坏机理、提高其使用的可靠性和预防其失效具有重要的理论和实际意义。本文比较了不同实验方法和测试技术的优缺点，对铁电陶瓷的电畴观测进行了综述，并简要总结了铁电陶瓷的畴变观测技术研究现状，指出了目前该领域研究中存在的问题。     

锰掺杂对硬性PZT材料压电性能的影响

研究了锰掺杂对ＰＺＴ材料微结构及压电性能的影响,并用ＥＳＲ确定了锰在ＰＺＴ材料中的价态．结果表明,锰在ＰＺＴ材料中主要以 Ｍｎ^２＋和 Ｍｎ^３＋的方式共存．锰在ＰＺＴ陶瓷材料中的“溶解度”约为１．５ｍｏｌ％．锰含量＜０．５ｍｏｌ％时,Ｍｎ将以Ｍｎ^２＋和Ｍｎ^３＋的方式优先进入晶格 Ｐｂ位,使材料的压电性能提高,表现出施主杂质特性;锰浓度处于 ０．５～１．５ ｍｏｌ％时,部分Ｍｎ将以Ｍｎ^３＋或Ｍｎ^２＋的方式进入晶格中（Ｚｒ;Ｔｉ）位,而此浓度范围内锰掺杂的ＰＺＴ材料同时表现出“软性”和“硬性”材料的压电特性．锰含量＞１．５ｍｏｌ％时,过量的Ｍｎ将在晶界积聚,使压电活性降低．少量Ｆｅ的存在,可使Ｍｎ离子的溶解度降低,并起到抑制Ｍｎ^２＋和 Ｍｎ^３＋氧化的作用.     

Large electric-field-induced strain in ferroelectric crystals by point-defect-mediated reversible domain switching

Ferroelectric crystals are characterized by their asymmetric or polar structures. In an electric field, ions undergo asymmetric displacement and result in a small change in crystal dimension, which is proportional to the applied field. Such electric-field-induced strain (or piezoelectricity) has found extensive applications in actuators and sensors. However, the effect is generally very small and thus limits its usefulness. Here I show that with a different mechanism, an aged BaTiO(3) single crystal can generate a large recoverable nonlinear strain of 0.75% at a low field of 200 V mm(-1). At the same field this value is about 40 times higher than piezoelectric Pb(Zr, Ti)O(3) (PZT) ceramics and more than 10 times higher than the high-strain Pb(Zn(1/3)Nb(2/3))O(3)-PbTiO(3) (PZN-PT) single crystals. This large electro-strain stems from an unusual reversible domain switching (most importantly the switching of non-180 degrees domains) in which the restoring force is provided by a general symmetry-conforming property of point defects. This mechanism provides a general method to achieve large electro-strain effect in a wide range of ferroelectric systems and the effect may lead to novel applications in ultra-large stroke and nonlinear actuators.     

Modeling of poling behavior of ferroelectric 3–3 composites

Piezoelectric 3–3 composites are often prepared from unpoled PZT ceramics and polymer matrices. During the poling process the PZT cannot deform freely due to the clamping by the surrounding polymer, which after poling results in the occurrence of residual mechanical stress in the composite. Based on the multi-linear constitutive model of ferroelectric and ferroelastic piezoceramics, a nonlinear finite element analysis was performed within the representative volume element to model the poling behavior of this kind of composites, in which appropriate periodic boundary conditions were prescribed for the displacements and the electric field of the composites. Considering the fact from experimental data that changes of the remanent strain induced by the switching process are volume preserving, we introduced different criteria in evaluating the maximum and minimum values of the ferroelastic strain S^f. A numerical simulation was then conducted to investigate the effects of different poling voltages and volume fractions of the PZT ceramic on the distribution of residual mechanical stress in the PZT of composites. The results show that if V_f < 18% a portion of the compressive mechanical stress in the poling direction on the PZT ceramic may cause a mechanical depolarization of the PZT ceramic.     

Temperature-dependent ferroelectric hysteresis properties of modified lead zirconate titanate ceramics

Temperature-dependent ferroelectric hysteresis properties of modified lead zirconate titanate ceramics have been investigated in a wide temperature range from 300 to 433 K. It is observed that remnant polarization, saturation polarization, and coercive field are increasing with an increase of the temperature in a low-field region and decreasing in a high-field region. Such behavior is explained by the competition between switching and backswitching mechanisms. A three-stage dependence of the logarithm of the hysteresis loop area on the logarithm of the electric field is identified. The temperature dependence of backswitching properties has been studied. The obtained results indicate that the temperature dependence of the polarization backswitching can be well described by the Arrhenius law. The activation energy for the domain switching determined from the fitting results exhibits decreasing tendency with the increase of the electric field.     

Effect of high energy electron irradiation on the electromechanical properties of poly (vinylidene fluoride-trifluorethylene) 50/50 and 65/35 copolymers

High energy electron irradiation with a broad range dosage was carried out on poly(vinylidene fluoride trifluorethylene) copolymer 65/35 mol% and 50/50 mol% films at different temperatures from room temperature to a temperature close to the melt temperature. The effect of irradiation on the properties of the films, such as electric field-induced strain, dielectric and polarisation behaviors, and mechanical modulus, is presented. The irradiated films can exhibit a very large electric field-induced strain, more than 4.5% longitudinal strain, and 3% transverse strain. The transverse strain of the stretched film can compare with the longitudinal strain; that of the unstretched film is much smaller than the longitudinal strain. With regard to the dielectric and polarization behaviors, we found that irradiation changes the copolymer from a typical ferroelectric to a relaxor ferroelectric in which the behavior of microregions under the electric field plays the key role. Between the two copolymers studied, we found that the 65/35 copolymer is preferred for both longitudinal and transverse strain generation. A model is proposed to explain the experimental results that the amplitude of the charge electrostrictive coefficient (Q) increases with decreasing crystallinity.     

One dimensional polar mechanical and dielectric responses of the ferroelectric ceramic PZT 65/35 due to domain switching

The constitutive relations and rate laws proposed by Chen and Peercy[l] have been successfully implemented in describing the one dimensional polar mechanical and dielectric responses of the ferroelectric ceramic PZT 65/35 to a slowly varying cyclic electric field ($\text{period > 1 s}$). In particular, we are interested in the consequences of domain switching due to the applied field and the results associated with the butterfly and hysteresis loops. An extensive experimental program has been carried out to obtain simultaneous time resolved measurements of the mechanical strain, the electric displacement and the applied field. The excellent agreement between numerical and experimental results indicates that we are beginning to gain considerable insight into the fundamentals of domain switching.     

Effect of starting raw materials on the dielectric, ferroelectric and electro-shape-memory properties of Mn3+ doped (Pb40Sr60)TiO3 ceramics

The effect of starting raw materials on the dielectric, ferroelectric and electro-shape-memory properties of 0.5 mol% Mn³⁺ doped (Pb₄₀Sr₆₀)TiO₃ ceramics was systematically studied. SEM observation showed that the ceramics fabricated from Pb₃O₄, SrCO₃, TiO₂ and MnCO₃ possessed the most homogeneous microstructure and the largest grain size. As the macroscopic consequence, such ceramics exhibited large dielectric property and well-developed double hysteresis loop. More interestingly, it showed large digital-like recoverable electrostrain of 0.11 % under the electric field of 3 kV/mm, which can rival the widely used linear piezoelectricity of the hard PZT ceramics. Defect distribution within the large and homogenous grains was analyzed to explore the microscopic origin of the simultaneous domain switching behavior and the digital-like strain properties. Such feature indicated the importance of material processing on the on/off-characterized electromechanical applications.     

Measurement of Structural Changes in Tetragonal PZT Ceramics under Static and Cyclic Electric Fields Using a Laboratory X-ray Diffractometer

In situ structural characterization techniques that are capable of characterizing piezoelectric ceramics under different electrical loading conditions are important to understand the behavior of materials during their use. In this work, we report the use of a laboratory X-ray diffractometer for the measurement of various structural changes in tetragonal La-doped lead zirconate titanate (PZT) ceramics under the application of static and cyclic electric fields. The changes in the volume fractions of the 90° domains parallel to the electric field direction are calculated from the intensities of the {002} diffraction peaks. In addition, the components of lattice strains are monitored from the changes in the (111) crystallographic planes. It is observed that, under the application of static electric fields, both 90° domain switching and the 111 lattice strains showed similarity with the macroscopic strainelectric field hystersis loop. To measure the structural changes under cyclic electric fields, a time-resolved X-ray diffraction technique was used. Under application of a square-wave electric field of amplitude ±650 V/mm and frequency 0.3 Hz, a change of ~5% in the volume fraction of the 90° domains and ~0.07% strain of the 111 lattice planes are observed. Both the amount of 90° domain switching and the 111 lattice strains are observed to increase with an increase in the amplitude of the cyclic electric field. The implications of the measured structural changes for the macroscopic piezoelectric properties of ceramics are discussed.     

Effects of porosity on electric fatigue behaviour in PLZT and PZT ferroelectric ceramics

Electric fatigue, namely the decay of the polarization and the consequent elastic strain with increased number of switching cycles under high a.c. field, severely limits the applications of ferroelectric and piezoelectric materials in high-strain electro-mechanical actuators and in thin films used in non-volatile memory devices. Electric fatigue tests have been conducted on lead zirconate titanate (PZT) and lanthanum-doped lead zirconate titanate (PLZT) ferroelectric ceramics. It was found that electric fatigue can be initiated by various factors, the porosity being one of them. Electric fatigue occurred in low-density(93%–97%) PLZT 7/65/35 ceramics after 10⁴ switching cycles, while the high-density (>99%) PLZT specimens of the same composition did not fatigue after 10⁹ switching cycles. It was also observed that for PZT ceramics, fatigue proceeded much more slowly in the samples with higher density (～98%) than those with lower densities (92%–96%). A tentative explanation for the origin of the fatigue mechanism associated with porosity is proposed.     

TiO2含量对压电纤维复合材料抗拉及驱动应变性能的影响

采用粘稠塑性加工方法制备了锆钛酸铅方形压电纤维复合材料, 研究了环氧树脂中不同TiO₂含量对压电纤维复合材料的电学阻抗、抗拉及驱动应变性能的影响。结果表明: 环氧树脂中TiO₂含量不同, 压电纤维复合材料的谐振频率不同。压电纤维复合材料的抗拉强度及纵向自由应变值均随着环氧树脂中TiO₂含量增大先增加后减小。环氧树脂中TiO₂含量为3wt%的压电纤维复合材料的抗拉强度达到了77.50 MPa, 且在驱动电压为-500 V~+1500 V时, 其纵向自由应变值达到了1783.7 με。当环氧树脂中TiO₂含量从3wt%增大至5wt%时, 压电纤维复合材料的抗拉性能和驱动应变性能均有所降低。在不同的外加驱动频率下, 压电纤维复合材料表现出不同的驱动应变能力。随着频率的增大, 压电纤维复合材料的纵向自由应变幅度表现出明显降低, 当频率超过5 Hz后, 其纵向自由应变值略有减小。     

Ferroelectricity in highly ordered arrays of ultra-thin-walled Pb(Zr,Ti)O3 nanotubes composed of nanometer-sized perovskite crystallites

We report the first unambiguous ferroelectric properties of ultra-thin-walled Pb(Zr,Ti)O 3 (PZT) nanotube arrays, each with 5 nm thick walls and outer diameters of 50 nm. Ferroelectric switching behavior with well-saturated hysteresis loops is observed in these ferroelectric PZT nanotubes with P r and E c values of about 1.5 microC cm (-2) and 86 kV cm (-1), respectively, for a maximum applied electric field of 400 kV cm (-1). These PZT nanotube arrays (10 (12) nanotubes cm (-2)) might provide a competitive approach toward the development of three-dimensional capacitors for the terabyte ferroelectric random access memory.     

Seeding effects on crystallization and microstructure of sol-gel derived PZT fibers

Dense and fine micro-structured lead zirconate titanate (PZT) fibers were successfully fabricated by sol-gel process from lead acetate dehydrate, zirconium normal butoxide, and titanium isopropoxide. An addition of perovskite seed particles (2 wt%) can lower the formation temperature of the perovskite phase and a single-phase perovskite PZT fiber can be obtained by heat-treating the precursor fiber at 500°C. Crystallization of perovskite phase was improved with the seed content. The diffraction peaks of (200) and (002) in the PZT fiber with 6 wt% seed was better split than in the PZT fiber without seed, which indicates that the tetragonality of PZT fiber was increased by adding seed particles. Seed particles also affected microstructure development of the PZT fibers.     

Design and fabrication of functionally graded PZT/Pt piezoelectric bimorph actuator

A laminated piezoelectric bimorph actuator with a graded compositional distribution of PZT and Pt was fabricated, and its deflection characteristics were evaluated. Using experimentally determined compositional dependency of elastic and piezoelectric properties in the PZT/Pt composites, the modified classical lamination theory and the finite element method were applied to find the optimum compositional profile that will give a larger deflection and smaller stress, simultaneously. The miniature bimorph-type graded actuator that consists of a composite internal-electrode (PZT/30 vol% Pt) and three piezoelectric layers of different compositions (PZT/0–20 vol% Pt) were fabricated by powder stacking and sintering. The deflection of the actuator was measured using electric strain gages mounted on the top and bottom surfaces of the actuator. The deflection was found to strongly depend on the composition distribution profile. Under an applied electric field of 100 V m^–1, the actuator with an optimum composition profile exhibited a curvature of up to 0.03 m^–1, which is a satisfactory performance for this kind of actuators. The stress generated on actuation was estimated to be as low as 0.4 MPa, which is much smaller than those of conventional directly bonded actuators and will assure a long actuation life.