Certain characteristics of electrically excitable mechanical resonant modes of a virgin PZT65/35 disc

In this paper we present experimental measurements of the in-phase and quadrature components of the axial mechanical displacements of particular flexural resonant modes exhibited by a virgin PZT65/35 disc specimen which is driven by alternating voltages. In particular, it is shown that the in-phase components of those resonances with nodal diameters exhibit the vibrational patterns due to a new electric-to-mechanical coupling phenomenon and the vibrational patterns which mimic the resonant mode shapes given by the quadrature components. We also present results concerning the frequency dependences of the in-phase and quadrature components in the neighborhoods of the resonances.     

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.     

PLZT陶瓷靶材及溅射薄膜的微观结构研究

研究了铁电ＰＬＺＴ（７．５／６５／３５）陶瓷靶材及用射频磁控溅射法制备的相同组分陶瓷薄膜的矿物结构及显微结构。实验结果表明，与陶瓷靶材相比，陶瓷薄膜的结晶取向发生了较大的变化，晶粒度减小，致密度提高，但晶粒无完整的晶形。随退火温度的提高，薄膜的缺陷明显增加。     

Certain characteristics of electrically excitable mechanical resonances in PZT 65/35

Summary In this paper, we examine certain characteristics of two electrically excitable mechanical resonances exhibited by two different specimens of the ferroelectric ceramic PZT 65/35. In particular, we determine the phase angle between the charge and the driving voltage, the current in the circuit, the amplitude of the mechanical displacement, and the electrical power dissipated in driving the specimens at each of these resonances for increasing amplitude of the driving voltage. It is shown that the phase angle, the current and the power dissipated have similar characteristics for the two resonances; but their mechanical displacements have entirely disparate features. In one case the amplitude increases more than linearly with respect to the driving voltage, whereas the contrary is true in the other case.With 5 Figures     

Dielectric and Ferroelectric Properties of Complex Perovskite Ceramics Under Compressive Stress

Dielectric and ferroelectric properties of complex perovskite PZT-PZN ceramic system were investigated under the influence of the compressive stress. The results showed that the dielectric properties, i.e. dielectric constant ( εr ) and dielectric loss ( tan δ), and the ferroelectric characteristics, i.e. the area of the ferroelectric hysteresis loops, the saturation polarization ( P(sat) ), and the remnant polarization (Pr) changed significantly with increasing compressive stress. These changes depended strongly on the ceramic compositions. The experimental results on the dielectric properties could be explained by both intrinsic and extrinsic domain-related mechanisms involving domain wall motions, as well as the de-aging phenomenon. The stress-induced domain wall motion suppression and non-180° ferroelectric domain switching processes were responsible for the changes observed in the ferroelectric parameters. In addition,a significant decrease in those parameters after a cycle of stress was observed and attributed to the stress induced decrease in switchable part of spontaneous polarization. This study clearly show that the applied stress had significant influence on the electrical properties of complex perovskite ceramics.     

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.     

A finite element prediction of ferroelectric switching behavior using a regular dodecahedron RVE

Some piezoelectric ceramic materials do behave in a nonlinear way when they are subjected to large electric or mechanical stress fields. This macroscopic nonlinearity comes from microscopic domain switchings during which one type of variant switches to other types of variants under large electromechanical fields. This switchable piezoelectric ceramic materials are called ferroelectric ceramics. In the present paper, a typical ferroelectric material particle is represented by a regular dodecahedron representative volume element (RVE) which includes twenty distinct types of variants, and a finite element analysis is carried out on a cubic specimen subjected to both a constant compressive stress and an electric field cycling. The calculation results are compared with experimental observations and isotropy of the responses is discussed.The authors gratefully acknowledge the support of the Agency for Defense Development through Grant ADD 01-05-01.     

0-3/1-3混合连通型铁电陶瓷-铁电聚合物的热释电性

推导出了0-3/1-3混合连通型铁电陶瓷-铁电聚合物的热释电系数表达式, 并详细讨论了陶瓷体积分数 v₂和陶瓷颗粒粒径与膜厚比(G/t)分别对复合材料的热释电系数p_c及p_c/ε_c(ε_c为复合材料的介电常数)的影响。结果表明: 当G/t≥0.5时, 不同陶瓷体积分数复合材料的热释电系数p_c均趋向于某个定值, 说明此时G/t对热释电系数的影响可忽略不计; 另外当陶瓷体积分数为0.1时, 随着G/t的增大, p_c /ε_c出现一个极大值, 且当G/t=0.9时, p_c /ε_c比纯PZT陶瓷的大8倍, 表明此条件为最佳工艺条件。而且, 在低陶瓷体积分数和低G/t比时, 理论曲线与实验数据符合较好。      

PLZT 透明铁电陶瓷晶粒长大的体视学研究

本工作用热压 8/65/35 PLZT 陶瓷为原始材料,通过不同热处理过程制备出各种不同晶粒度的陶瓷试样,试样经过热腐蚀后,用 Cambridge Instruments Ltd 的 Quantimet 900对它们进行图像分析和定量体视学研究,获得了很有价值的各种数据。     

Domain switching in polycrystalline ferroelectric ceramics

Ferroelectric ceramics are widely used as sensors and actuators for their electro-mechanical properties, and in electronic applications for their dielectric properties. Domain switching--the phenomenon wherein the ferroelectric material changes from one spontaneously polarized state to another under electrical or mechanical loads--is an important attribute of these materials. However, this is a complex collective process in commercially used polycrystalline ceramics that are agglomerations of a very large number of variously oriented grains. As the domains in one grain attempt to switch, they are constrained by the differently oriented neighbouring grains. Here we use a combined theoretical and experimental approach to establish a relation between crystallographic symmetry and the ability of a ferroelectric polycrystalline ceramic to switch. In particular, we show that equiaxed polycrystals of materials that are either tetragonal or rhombohedral cannot switch; yet polycrystals of materials where these two symmetries co-exist can in fact switch.     

Direct and simultaneous observation of ferroelectric and magnetic domains

The ferroelectric/magnetic domain structure in a magnetoelectric binding BaTiO₃/Fe₈₁Ga₁₉ and the ferroelectric/crystallographic domain structure in a magnetoelectric binding PMN-34PT/Mn₅₀Ni₂₈Ga₂₂ were observed successfully by scanning electron acoustic microscopy (SEAM). Both the stripe ferroelectric domains in single crystals and the stripe magnetic domains in polycrystalline grains are obtained simultaneously, which exhibits that the scanning electron acoustic microscopy is a unique imaging technique. In addition, the experimental results show that the SEAM technique may be used in multiferroics to character two or more ferroic domains simultaneously. The imaging mechanisms of ferroelectric domains, magnetic domains, and crystallographic domains are attributed to piezoelectric coupling mechanism, magneto–elastic coupling mechanism, and thermo–wave coupling mechanism, respectively.     

PIMNT单晶弯曲圆盘换能器设计

新型弛豫铁电单晶材料铌铟酸铅-铌镁酸铅-钛酸铅晶体(Pb(In_1/2Nb_1/2) O₃-Pb(Mg_1/3Nb_2/3) O₃-PbTiO₃, PIMNT)的压电系数是陶瓷材料的 6 倍以上,应变量高出压电陶瓷 10 倍以上,具有较高的机电耦合系数,压电性能优于传统 PZT 材料。文章将单晶材料应用于带空气腔的弯曲圆盘换能器中,利用 ANSYS 仿真软件优化换能器结构,确定换能器尺寸,设计制作 PIMNT 压电单晶换能器和PZT4压电陶瓷换能器,并进行了水池实验。换能器实测结果与仿真结果保持一致,单晶换能器的谐振频率为 2.85 kHz,最大发送电压响应为 136.3 dB。结果表明,相比于同尺寸的陶瓷换能器,将 PIMNT 压电单晶应用于弯曲圆盘换能器可降低谐振频率,提高发送电压响应,提升换能器的工作性能,为进一步改善单晶换能器综合性能提供参考。     

A theory of the influences of space-charge field on domain switching in PLZT 7/65/35 ceramic

Summary In this paper we propose a phenomenological theory to explain the influences of a stored space-charge field on domain switching in the electrooptic ceramic PLZT 7/65/35, and show that the resulting numerical predictions of the strain versus electric field curve (butterfly loop) and the electric displacement versus electric field curve (hysteresis loop) are in qualitative agreement with those obtained experimentally. In particular, the stored space-charge field can prohibit as much as 50% of the dipoles from switching in any direction via the application of an external electric field alone; it can also prohibit some of the remaining dipoles from being aligned in the direction opposite to it. We believe that these are the first quantitative results in this regard.With 9 Figures     

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.     

Birefringent light scattering in PLZT ceramics

A model for visible light scattering in thin, ferroelectric ceramic plates is presented. This and other previously published models are compared with experimental results. An expression for scattered light intensity over exit angle is developed on the basis of multiple refraction from randomly oriented grain and domain walls in a birefringent medium and is compared to measurements of longitudinal-mode light scattering from thin (~250-650-mum) PLZT plates of three different ceramic compositions. The characteristic differences in the observed light scattering are attributed to two physical mechanisms that are related to field-induced ferroelectric anisotropies.     

弛豫多铁性材料研究进展

多铁性材料同时具有多种铁性(铁电性、铁磁性或铁弹性)的有序, 可实现电磁信号的相互控制, 成为近年来研究热点。在具有成分无序的复杂体系中, 长程铁性有序有可能被打破, 材料将表现出弛豫特性。我们将至少存在一种铁性弛豫特性的多铁性材料称之为弛豫多铁性材料。这类多铁性材料的极化强度(或磁化强度)在外加电场(或外加磁场)作用下响应更加灵敏, 其磁电耦合机制与长程有序的多铁性材料不同。本文结合国内外最新研究成果, 首先介绍了和弛豫铁性有序相关的物理概念, 重点阐述了多铁性材料在铁电和铁磁双弛豫态下的磁电耦合机制; 然后, 详细介绍了钙钛矿结构(包括PbB₁B₂O₃基和BiFeO₃基材料)和非钙钛矿结构(包括层状Bi结构和非正常铁电体)弛豫多铁性材料的研究进展; 最后, 对该领域亟待解决的问题进行了展望。     

Quantitative histomorphometric evaluation of spinal arthrodesis after biphasic calcium phosphate ceramic implantation in sheep

The effectiveness of a macroporous biphasic calcium phosphate ceramic was studied after laterovertebral arthrodesis in sheep. A ceramic with a TCP/HAP ratio of 35/65 was compared with autogenous bone graft 1, 3, 6, 9 and 12 months after implantation. Surface, lengths, and relative pore parameters have been quantified by using light microscopy and image analysis. Quantitative analysis of the results indicated that the biphasic ceramic allows an arthrodesis after 12 months, although control graft is effective after six months. The implanted material is still present after 12 months. Degradation of the ceramic is initially fast, then slows down. The intra-implant new bone formation reaches 15% after three months and 19% after 12 months. In contrast, bone ingrowth increases from 9% after three months to 23% after 12 months in intertransverse zone. Bone formation was seen with a higher frequency in pores of 240–480 µm in average diameters. New bone fills only one part of the area of a pore. A spinal fusion can be obtained with this biphasic ceramic, but the use of this material cannot be currently recommended without further investigations.     

Uniaxial electromechanical behavior of ferroelectric ceramic PZT-53

Effect of compressive pre-stress and biased electrical field on the uniaxial electromechanical behavior of a soft ferroelectric ceramic PZT-53 is investigated. The emphasis is on the effect of electric and mechanical loading history upon the response of PZT-53 to external loading and on the effect of pre-stress and biased electrical field upon the electro-mechanical coupling behavior. It is found that the uniaxial behavior of the PZT-53 is sensitive to the compressive pre-stress and biased electrical field, and is less sensitive to the loading history. Obtained results are expected to shed insightful light on developing reliable constitutive model for ferroelectric ceramics.     

The domain switching and structural characteristics of PLZT bulk ceramics and thin films chemically prepared from the same acetate precursor solutions

Lead lanthanum zirconate titanate (PLZT) ferroelectrics were produced in bulk ceramic and thin-film form from the same acetate precursor solutions in order to compare their electrical and physical properties. Bulk ceramics were hot pressed from chemically coprecipitated powders, and thin films were fabricated by spin coating on silver foil and platinum-coated silicon wafer substrates. A number of PLZT compositions were investigated, including ferroelectric memory materials near the morphotropic phase boundary with 2% La, memory and slim-loop ferroelectric x/65/35 (La/Zr/Ti) compositions with up to 12% La, as well as some antiferroelectric thin-film materials. Internal film stress from thermal expansion mismatch between films and substrates was found to contribute to differences in electrical properties and Curie temperatures between the thin film and bulk materials, as were interface layers between the films and substrates, mechanical clamping from the substrates and grain size.