铁电马氏体中的电致形状记忆效应

与温度驱动形状记忆的缓慢响应及磁场驱动形状记忆的巨大体积相比较,电场驱动形状记忆具有响应快和体积小的优点.但是,基于传统反压电效应的电场驱动形状记忆由于变形量较小而收到限制.本研究表明,通过运用基于点缺陷短程序对称性遵循的普适性原理的可逆畴翻转机制,可以在铁电马氏体中获得巨大的电致形状记忆效应;其产生的变形量理论上是反压电效应所产生变形量的几十倍.采用原位畴观察实验给出了可逆畴翻转的直接证据.并且,在铁电多晶陶瓷中也获得了这种大的电致形状记忆效应.这种效应在很宽的频率范围内都很稳定,在疲劳测试中也显示了很好的可靠性.运用这一新的电致形状效应有望制备出新一代非线性驱动器材料.     

无铅陶瓷中的电致伸缩效应

电致伸缩是一个二次方效应,应变正比于极化强度的平方,比例系数称为电致伸缩系数[Qij].一般固体电介质都能产生电致伸缩效应.对立方晶系的材料来说,电致伸缩系数张量为 当外加电场沿方向1时,E2=E3=0,纵向应变为通过测量材料的应变与外加电压的关系Xi～Vi,和极化强度与外电场的关系P1～Ei,就可以求得电致伸缩系数 电致伸缩效应在天文学、光学通信、激光调制等方面有着广泛的应用.与压电效应相比,它具有重复性好,不需极化,无老化问题等优点.电致伸缩是一个二次方效应,一般较小,不易观察到.已经发现,在具有扩散相转变特征的铁电固溶体中,当…     

Si掺杂HfO_2薄膜的铁电和反铁电性质

通过改变Si掺杂量制备出了具有显著铁电和反铁电特征的HfO2纳米薄膜,对其电滞回线、电容-电压和漏电流-电压特性以及物相温度稳定性进行了对比研究.反铁电薄膜的介电系数大于铁电薄膜,在电场加载和减载过程中发生的可逆反铁电-铁电相变导致了双电滞回线的出现,在室温至185℃的测试温度范围内未出现反铁电→顺电相变.在电流-电压特性测量时观察到的负微分电阻效应归因于极化弛豫等慢响应机理的贡献.     

球形无规键无规场模型研究弛豫铁电体极化效应

基于球形无规键无规场模型和电场作用下弛豫铁电体微畴-宏畴机理,利用模糊畴界观点以及电场对极化的分数维效应,分析了电场对畴的作用机理.研究结果表明:电场对畴的诱导偶极子增量的极化效应导致了电滞回线的不饱和及相关的大的电致伸缩效应;而畴的偶极子增量耦合时结合能的变化对低电场的电滞回线略有影响,但基本不会改变高电场时的极化状态.初始微畴大小对电滞回线非常重要,细小的微畴会导致细长的电滞回线及电场与电致伸缩良好的线性关系.     

利用X射线衍射技术对压电材料本征与非本征起源探究的研究进展

钙钛矿铁电压电材料具有高介电压电常数和高机电耦合系数等特点,在工业、消费电子和军事等领域具有广泛的应用,其压电性能起源的机理及与材料多尺度结构之间的关系一直是凝聚态物理和材料科学领域的研究热点.铁电材料的压电效应主要来源于本征的场致晶格畸变以及非本征的畴翻转和畴壁运动,理解并区分这两种压电效应的贡献机制对研究材料压电性能的起源具有重要意义.本文综述了近年来通过电场原位X射线衍射技术分析电场作用下材料晶格结构和畴结构变化的技术手段和研究方法,重点介绍了自第三代同步辐射光源和高速探测器获得长足发展以来,通过时间分辨衍射技术、单双峰拟合、全谱拟合、质心计算等方法开展压电材料本征和非本征贡献,以及电场诱导相变对其宏观性能影响的研究进展,期望通过对各类方法的介绍和回顾为多种压电材料的机理分析提供研究方法和技术支持.     

逆压电效应与电致伸缩效应

可能是由于顾名思义的缘故,人们[1-4]常把电致伸缩效应称之为逆压电效应,认为逆压电效应就是电致伸缩效应.其实,逆压电效应与电致伸缩效应是截然不同的两种概念. 1880年,居里兄弟(Pierre and JacquesCurie)发现了压电效应,即某些不具有中心对称性结构的晶体.沿某些方向受压时,其表面产生束缚电荷,电荷量正比于所受的压力.历史上称该效应为正压电效应.1881年,居里兄弟又证实了Lippmann关于存在逆压电效应的预言,即具有正压电效应的晶体在外电场作用下会发生形变,形变与外场成正比,外场极性反转,形变符号也随之改变.人们称该效应为逆压电效…     

PZT铁电薄膜纳米尺度铁电畴的场致位移特性

利用扫描力显微术的压电响应模式，并基于逆压电效应原理，研究了梯度组成的PZT铁电薄膜纳米尺度铁电畴的场致位移特性.获得了源于纳米尺度铁电畴的压电效应和电致伸缩效应贡献的场致位移回滞线，以及源于线性压电效应和电畴反转效应综合贡献的纳米尺度压电位移 场强蝶形曲线，证实了Caspari Merz理论在纳米尺度上的有效性.发现了梯度铁电薄膜存在纳米尺度印刻现象，认为该现象的内因源于薄膜中的内偏场. 关键词： PZT铁电薄膜 场致位移 纳米尺度 扫描力显微术     

强电场作用下反铁电锆钛酸铅的介电行为研究

采用电滞回线方法和偏置直流电场中叠加小交变电场方法研究了锆钛酸铅反铁电陶瓷材料在强电场作用下的介电行为.测量结果显示，锆钛酸铅反铁电材料的介电常数随外加电场强度呈非线性变化，在反铁电 铁电转变的电场区间形成介电峰.表征极化强度随电场强度变化率的微分介电常数εd峰值出现在反铁电 铁电转换电场强度处，最高达到41000.随着偏置电场增加反铁电向铁电体转变过程中，小信号介电常数εc减小；在电场降低铁电回复成反铁电过程中，小信号介电常数εc增大，小信号介电常数εc峰先于微分介电常数εd峰出现.根据电场作用下反铁电 关键词： 锆钛酸铅反铁电陶瓷 介电行为 强电场条件     

具有形状记忆效应的反铁电材料的制备及其相变行为的研究

研究表明，铁电与反铁电材料在形状记忆方面与合金具有相似的性质，用变温Ｘ射线衍射来研究Ｐｂ０．９７Ｌａ０．０２（Ｚｒｏ０．６５Ｔｉ０．１０Ｓｎ０．２５）Ｏ３在升温过程中的相变并测得在相变的同时晶面间距ｄ有明显的跳变。还用相变潜热测量（ＤＳＣ）与电滞回线测量证实了在各个温区的相     

1-3型纳米多铁复合薄膜中电场诱导的磁化研究

运用Landau-Devonshire热力学唯像理论,考虑铁电相和铁磁相的电致伸缩、磁致伸缩效应以及产生于铁电/铁磁和薄膜/基底界面的弹性应力作用,两次重整介电和磁作用系数得到了这种多铁系统在Landau自由能函数下的本征二次方磁电耦合形式,从而研究了外延1-3型纳米多铁复合薄膜中极化、磁化随薄膜厚度、温度的变化以及该薄膜中外加电场诱导的磁化变化.结果表明薄膜平面内的应压力的弛豫使得磁化强度和极化强度随薄膜厚度的增加而减少,外加电场不仅能诱导铁电相极化场翻转,而且由于铁电和铁磁相界面竖直方向的弹性耦合导致 关键词： 多铁 磁电效应 磁致伸缩 薄膜     

Thickness-dependent of conduction mechanism and bias electric field modulation of transport properties for SrRuO3/PMN-PT heterostructures

Ultra-thin SrRuO₃ (SRO) films have been grown on ferroelectric and piezoelectric PMN-PT substrates. The structural properties of these films have been characterized by atomic force microscopy, x-ray diffraction and cross-sectional transmission electron microscopy. The nature of electric transport was analyzed in detail and the conduction mechanism of SRO films evolves through three regimes: from a three-dimensional (3D) metallic through a weakly localized to a strongly localized behavior as film thickness is reduced. The bias electric field modulations of transport properties and magnetic properties were explored for these films. We also demonstrate that ferroelectric (FE) domain switching induces a reversible tuning of the magnetic and electric properties in SRO/PMN-PT heterostructure. The FE domain switching in the substrate contributes to an in-plane strain that changes the spin exchange coupling in the SRO layer, and therefore results in a reversible resistance difference of up to 16%. This modulation effect on the electric properties by an electric field demonstrates great potential for the applications of all-oxides spintronics devices.     

Can an electric field induce an antiferroelectric phase out of a ferroelectric phase?

It has been widely accepted that electric fields favor the ferroelectric phase with parallel electric dipoles over the antiferroelectric phase. With detailed measurements in polycrystalline ceramics of Pb(0.99)Nb(0.02[(Zr(0.57)Sn(0.43)(1-y)Ti(y)](0.98)O(3), we demonstrate in this Letter that electric fields can induce an antiferroelectric phase out of a ferroelectric phase, i.e., trigger an apparently unlikely ferroelectric-to-antiferroelectric phase transition. We suggest that it is caused by the volume contraction from the converse piezoelectric effect at the coercive field with a reversed polarity.     

The effect of annealing temperature on the morphology and piezoelectric characteristics of BaTiO3 nanofibers and domain switching under different temperatures

Effects of annealing temperature (600–750 °C) on crystalline structure, the morphology and piezoresponse hysteresis loops of BaTiO₃ nanofibers prepared by electrospinning are characterized by X-ray diffraction, scanning electronic microscopy, transmission electron microscope and piezoresponse force microscope. When the annealing temperature is 700 °C, the nanofibers become smoother and have a diameter of 100–300 nm. Meanwhile the typical butterfly-shaped amplitude loop and 180°phase change represents the best ferroelectric and piezoelectric properties at 700 °C. So the 700 °C was found to be optimum for good piezoelectric characteristics at annealing temperature of 600 °C–750 °C. In order to give more clear evolution of domain states at different external fields, the three dimensional topographic and phase images of the nanofiber at different temperatures are observed by piezoresponse force microscope. The 90° domain switching is observed during heating from room temperature to 125 °C and the domain switching tends to be stable when the temperature exceeds a critical value. The thermal stress due to the high temperatures is responsible for switching mechanism from the perspective of equilibrium state free energy. This work suggests that the temperature variation should be considered while designing the ferroelectric devices based on one dimensional material.     

Generation and relaxation of reactive stresses in a Cu-Al-Ni shape memory alloy upon cyclic temperature variation in the range 293–800 K

The generation and relaxation of reactive stresses in Cu-Al-Ni shape-memory alloy single crystals studied during a single cycle of temperature variation in the range 293–800 K under conditions of the β-phase decomposition (above 600 K) are found to depend on the degree of β-austenite decomposition at the stage of decreasing temperature. The higher this degree, the lower the stresses relaxed and generated upon decreasing temperature and the higher the critical temperatures of the reverse martensitic transitions. Moreover, loading the alloy by reactive stresses during a heating half-cycle causes not only a reversible martensitic shape memory deformation but also an additional austenitic shape memory deformation to occur when the temperature is decreased.     

Two-way reversible deformation in titanium nickelide

A systematic study has been made of the shape-memory effects which arise in titanium nickelide after prestraining under isothermal conditions. It has been found that under thermal cycling in the free state a broad spectrum of phenomena is observed — repeatedly reversible shape memory, reversible deformation, deformation of an oriented transformation, etc., each of which can be realized independently of the others in the temperature range of the B2 R and R B19' transformations. When summing up the observed laws of the mechanical behavior of the material we used concepts of heterogeneous development of deformation in crystals, structurally hereditary properties of alloys with a shape-memory effect, as well as the principle of independent initiation of various channels of deformation.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 71–76, August, 1988.     

Dynamic hysteresis in ferroelectric systems: experiment and Monte Carlo simulation

A Monte Carlo algorithm for dynamic hysteresis simulation in ferroelectric spin systems is developed based on a DIFFOUR model in which the local spontaneous polarization is defined by the double-well potential energy and the nearest-neighbor spin interaction as well as an external electrical field of variable amplitude and frequency. A direct measurement of the hysteresis loop for ferroelectric Pb(Zr_0.52Ti_0.48)O₃ thin film capacitors using the Sawyer–Tower technique is performed. Significant dependence of the hysteresis shape and pattern on the external field is revealed. Direct imaging of the simulated domain pattern indicates serious suppression of the domain switching over the high-frequency range. The evaluated scaling relations from the simulation for remanence, coercivity, and the area of the hysteresis over the low-frequency range are supported by theoretical predictions and experiments, but the high-frequency scaling behaviors as derived are different from one and another. Received: 23 January 2001 / Accepted: 17 August 2001 / Published online: 20 December 2001     

Orientational contribution to the piezoelectric constants of BaTiO3 ceramic in ferroelectric phases with various symmetries

A self-consistent method based on the interaction of a piezoelectric sphere with a piezoelectric medium that has anisotropic elastic and dielectric properties is used to calculate the components of the tensor piezoelectric modulus of BaTiO₃ ceramic in all three ferroelectric modifications. A comparison of the calculated and measured piezoelectric moduli shows that at least 60–70% of the piezoelectric effect in BaTiO₃ ceramic is caused by domain boundary movement throughout the entire ferroelectric region. Fiz. Tverd. Tela (St. Petersburg) 41, 1080–1083 (June 1999)     

Nanosecond domain wall dynamics in ferroelectric Pb(Zr, Ti)O(3) thin films

Domain wall motion during polarization switching in ferroelectric thin films is fundamentally important and poses challenges for both experiments and modeling. We have visualized the switching of a Pb(Zr, Ti)O(3) capacitor using time-resolved x-ray microdiffraction. The structural signatures of switching include a reversal in the sign of the piezoelectric coefficient and a change in the intensity of x-ray reflections. The propagation of polarization domain walls is highly reproducible from cycle to cycle of the electric field. Domain wall velocities of 40 m s(-1) are consistent with the results of other methods, but are far less than saturation values expected at high electric fields.     

New polymer-containing piezoelectric materials

A review is presented of the data on the design of polymer-containing piezoelectric materials: electrets exhibiting a piezoelectric effect, ferroelectric polymers, piezoelectric composites (piezoelectric ceramic + polymer), and new piezoelectric polymer materials, such as piezoelectrics based on porous polymers and elastic active dielectrics, whose piezoelectric properties considerably surpass the characteristics of conventional piezoelectric materials, as well as the characteristics of electromechanical and mechanoelectrical transducers operating in receiving, generating, and deformation-inducing modes.     

Nonlinear constitutive behavior of ferroelectric materials

The ferroelectric specimen is considered as an aggregation of many randomly oriented domains. According to this mechanism, a multi-domain mechanical model is developed in this paper. Each domain is represented by one element. The applied stress and electric field are taken to be the stress and electric field in the formula of the driving force of domain switching for each element in the specimen. It means that the macroscopic switching criterion is used for calculating the volume fraction of domain switching for each element. By using the hardening relation between the driving force of domain switching and the volume fraction of domain switching calibrated, the volume fraction of domain switching for each element is calculated. Substituting the stress and electric field and the volume fraction of domain switching into the constitutive equation of ferroelectric material, one can easily get the strain and electric displacement for each element. The macroscopic behavior of the ferroelectric specimen is then directly calculated by volume averaging. Meanwhile, the nonlinear finite element analysis for the ferroelectric specimen is carried out. In the finite element simulation, the volume fraction of domain switching for each element is calculated by using the same method mentioned above. The interaction between different elements is taken into account in the finite element simulation and the local stress and electric field for each element is obtained. The macroscopic behavior of the specimen is then calculated by volume averaging. The computation results involve the electric butterfly shaped curves of axial strain versus the axial electric field and the hysteresis loops of electric displacement versus the electric field for ferroelectric specimens under the uniaxial coupled stress and electric field loading. The present theoretical prediction agrees reasonably with the experimental results. Supported by the National Natural Science Foundation of China (Grant No. 10572138)