铁电陶瓷中电畴翻转研究进展

电畴为铁电陶瓷固有的独特微观组织特征之一,铁电陶瓷的许多性能均与其密切有关.综述了铁电陶瓷中的电畴结构,系统介绍了电场、机械作用引起的电畴翻转,概述了电畴翻转对铁电陶瓷断裂韧性的影响及其研究进展.     

升温对[100]cub弛豫铁电PMN-32PT单晶电畴组态演变的影响

采用热台偏光显微镜观察以ACRT+ Bridgman法获得、经过金相抛光处理的弛豫铁电PMN-32PT单晶[100]cub切型电畴组态,考察了未退火状态下[100]cub切型单晶的消光行为及连续升温对本征电畴与由抛光机械应力诱导非本征电畴组态的影响.结果表明,在升温过程中,PMN-32PT单晶非本征电畴在三方-四方铁电相变后消失;本征电畴组态的变化表现为两个阶段,第一阶段畴先细化后宽化,第二阶段进行铁电-顺电相变,相变过程缓慢,持续范围为168～177℃,且与三方-四方相变出现次序相反.     

多场耦合下铁电薄膜非线性行为的畴变模型

铁电薄膜在外加力场,电场和温度场的作用下表现出明显的非线性,为了更好的描述这种现象,本文提出了一个热-电-力耦合场铁电薄膜下的畴变模型。该模型基于细观力学模型,认为电畴自由能的改变提供电畴翻转的动力,且180°电畴翻转由两步90°翻转构成。在本构关系中加入了铁电薄膜制备过程中产生的残余应变项,以区别于块体铁电材料,通过该模型计算出了铁电薄膜在不同外场下的响应,结果与实验和其他模型的结果较为符合。     

复合钙钛矿铁电陶瓷的电场诱导畴反转特征研究

本文通过铌锌酸铅基复合钙钛矿结构铁电陶瓷的电畴观察、强场极化反转行为以及直流偏压下介电行为和X射线衍射峰等的详细测量,对铁电微畴、宏畴在外场诱导下的反转规律进行了分析,探讨了与铁电陶瓷介电行为相对应的微观极化机制。     

复合钙钛矿铁电陶瓷的电场诱导畴反转特征研究

本文通过铌锌酸铅基复合钙钛矿结构铁电陶瓷的的电畴观察,强场极化反转行为以及直流偏压下介电行为和Ｘ射线射衍射峰等的详细测量,对铁电微畴,宏畴在外场诱导下的反转规律进行了分析,探讨了与铁电陶瓷介电行为相对应的微观极化机制。     

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。     

PMNT单晶电畴结构随组分与结构的变化

利用多种方法观察了弛豫型铁电单晶ＰＭＮＴ中电畴结构随组分与结构的演变过程与特征．观察发现,在ＰＭＮ－ＰＴ的三方相区内,随ＰＴ含量的增加,电畴结构表现出微畴一（亚微畴）－不规则宏畴一规则宏畴转变历程;在三方－四方相变中,非１８０°电畴发生７１°（或１０９°）宏畴－９０°宏畴的转化,同时电畴图像变得更为规则．根据不同组分ＰＭＮＴ电畴的显示特征,提出晶体的最大双折射率可以作为度量其弛豫性强弱的光学参数．观察到了电畴的分布不均匀与多级结构现象,前者与组分或结构的起伏有关,后者与多期式马氏体转变有关．本文还分析了偏光显微镜、ＤＩＣ、ＳＥＭ、ＳＥＡＭ等观察方法中电畴的成像特征．     

粗大晶粒PZT陶瓷中电畴的结构

应用扫描力显微镜(SFM)的压电响应模式观测未经抛光处理的PZT陶瓷片的电畴结构,用纵向压电响应信号和侧向压电响应信号获得PZT陶瓷材料三维电畴结构.结果表明,将样品晶粒的微形貌与SFM的纵向和侧向压电响应信号相结合,能准确表征粗大晶粒样品的三维电畴结构.用SFM可观测表面不经任何处理的陶瓷样品的电畴,不会引入表面应力等影响因素,能得到样品的原生畴结构.对原生畴结构的观察表明,对于受应力较大的晶粒,成畴的主要原因是降低应变能,而受应力较小的晶粒成畴的主要原因是降低退极化能.     

近化学计量比LiNbO3晶体电畴结构观察和机理探讨

采用双坩埚提拉法(DCCZ)生长了各种不同成分的近化学计量比LiNbO3晶体,并用腐蚀法观察了其电畴结构.结果表明,化学成分对未经极化处理晶体的电畴结构起决定性作用,当Li2O含量处于49.4mol%附近时,晶体z面电畴呈现特殊的三次对称反畴;当晶体中Li2O含量为49.7mol%时,晶体为完全单畴.本文对其形成机理进行了探讨,认为在由顺电相向铁电相转变时,局部铁电畴的极性方向与该处沿z轴方向的温度梯度正负密切相关,z轴生长晶体时,由于相变发生所处位置离生长界面的距离受LiNbO3晶体计量比影响,所处温场固有温梯也随之不同,在此基础上解释了不同成分晶体的电畴结构形成原因.最后讨论了控制铁电畴结构的工艺措施.     

近化学计量比LiNbO3晶体电畴结构观察和机理探讨

采用双坩埚提拉法(DCCZ)生长了各种不同成分的近化学计量比LiNbO₃晶体, 并用腐蚀法观察了其电畴结构. 结果表明, 化学成分对未经极化处理晶体的电畴结构起决定性作用, 当Li₂O 含量处于49.4mol%附近时, 晶体z面电畴呈现特殊的三次对称反畴; 当晶体中Li₂O含量为49.7mol%时, 晶体为完全单畴. 本文对其形成机理进行了探讨, 认为在由顺电相向铁电相转变 时, 局部铁电畴的极性方向与该处沿z轴方向的温度梯度正负密切相关, z轴生长晶体时, 由于相变发生所处位置离生长界面的距离受LiNbO₃晶体计量比影响, 所处温场固有温梯也 随之不同, 在此基础上解释了不同成分晶体的电畴结构形成原因. 最后讨论了控制铁电畴结构的工艺措施.     

陶瓷材料相转变增韧的研究进展

介绍了几种相转变韧化机制，主要包括ZrO2相变增韧、铁电／压电性畴转变增韧、铁弹性畴转变增韧的增韧机理和研究进展。提出一种新的相转变增韧机制——铁磁性畴转变增韧机制，即利用铁磁相的磁畴转变或压磁效应来实现能量耗散，从而达到增韧效果，探讨了其可能性。     

铁电体尺寸对其开关特性的影响

应用铁电体极化反转的Orihara Ishibashi理论 ,讨论了圆形铁电薄膜和球形铁电体的开关电流以及开关时间对系统尺寸的依赖性。数值计算表明 ,不论是二维还是三维铁电系统 ,其铁电畴反转过程中产生的开关电流都随系统尺寸减少而下降 ,开关时间随系统尺寸减少而缩短     

Unexpectedly low barrier of ferroelectric switching in HfO2 via topological domain walls

Fluorite-structure ferroelectrics — in particular the orthorhombic phase of HfO₂ — are of paramount interest to academia and industry because they show unprecedented scalability down to 1-nm-thick size and are compatible with Si electronics. However, their polarization switching is believed to be limited by the intrinsically high energy barrier of ferroelectric domain wall (DW) motions. Here, by unveiling a new topological class of DWs, we establish an atomic-scale mechanism of polarization switching in orthorhombic HfO₂ that exhibits unexpectedly low energy barriers of DW motion (up to 35-fold lower than given by previous conjectures). These findings demonstrate that the nucleation-and-growth-based mechanism is feasible, challenging the commonly held view that the rapid growth of the oppositely polarized domain is impossible. Building on this insight, we describe a strategy to substantially reduce the coercive fields in HfO₂-based ferroelectric devices. Our work is a crucial step towards understanding the polarization switching of HfO₂, which could provide a means to solve the key problems associated with operation speed and endurance.     

外场下NBT-KBT100x压电薄膜畴变演化、保持特性及印记的研究

采用金属有机物分解法制备了不同K含量的弛豫型压电薄膜(1-x)Na_0.5Bi_0.5TiO_3-xK_0.5Bi_0.5TiO₃(NBT-KBT100x)。利用压电力显微镜研究了外场条件下纳米级铁电畴翻转, 以及保持性能和印记失效。结果表明: (1)不同组分中, NBT-KBT17薄膜单畴态的晶粒个数最多。选取NBT-KBT17薄膜分别测试了其面内极化分量和面外极化分量, 该薄膜的面内压电信号较强, 这说明薄膜在d₃₁模式下的压电响应明显。(2)选择NBT-KBT17薄膜中较大尺寸的单晶, 实现了对弛豫性铁电体的电畴写入。将其在大气环境下放置不同时间, 出现了退极化现象, 但总的畴态稳定, 表明其保持性能较好。(3)制备了NBT-KBT17原理型薄膜电容器, 分别测试了加载作用前后NBT-KBT17薄膜电容器的相位和振幅滞后回线图。结果表明外加作用力使相位回线向右发生了一定的移动, 且振幅的蝶形曲线均在不同方向上发生了偏移, 同时形状也发生了改变。最后, 利用空间电荷原理分析了外加力导致薄膜印记产生的机理。     

Fully coupled non‐linear analysis of piezoelectric solids involving domain switching

Domain switching is the cause of significant non‐linearity in the response of piezoelectric materials to mechanical and electrical effects. In this paper, the response of piezoelectric solids is formulated by coupling thermal, electrical, and mechanical effects. The constitutive equations are non‐linear. Moreover, due to the domain switching phenomenon, the resulting governing equations become highly non‐linear. The corresponding non‐linear finite element equations are derived and solved by using an incremental technique. The developed formulation is first verified against a number of benchmark problems for which a closed‐form solution exists. Next, a cantilever beam made of PZT‐4 is studied to evaluate the effect of domain switching on the overall force–displacement response of the beam. A number of interesting observations are made with respect to the extent of non‐linearity and its progressive spread as the load on the beam increases. Copyright © 2002 John Wiley & Sons, Ltd.     

Domain characteristics and chemical bonds of lithium niobate

Domain characteristics such as domain shape, domain switching, and etching rate at Z-surfaces of lithium niobate (LN) single crystals are comprehensively studied from the chemical bonding viewpoint. The present work shows that the domain characteristics are closely correlated to anisotropic bonding behaviors of constituent ions, which may be regarded as a microscopic reflection of detailed conditions of the chemical bonding geometry and strength of Li⁺ and Nb⁵⁺ cations in the LN crystallographic frame.     

Reproducible Ultrathin Ferroelectric Domain Switching for High-Performance Neuromorphic Computing

Neuromorphic computing consisting of artificial synapses and neural network algorithms provides a promising approach for overcoming the inherent limitations of current computing architecture. Developments in electronic devices that can accurately mimic the synaptic plasticity of biological synapses, have promoted the research boom of neuromorphic computing. It is reported that robust ferroelectric tunnel junctions can be employed to design high-performance electronic synapses. These devices show an excellent memristor function with many reproducible states (≈200) through gradual ferroelectric domain switching. Both short- and long-term plasticity can be emulated by finely tuning the applied pulse parameters in the electronic synapse. The analog conductance switching exhibits high linearity and symmetry with small switching variations. A simulated artificial neural network with supervised learning built from these synaptic devices exhibited high classification accuracy (96.4%) for the Mixed National Institute of Standards and Technology (MNIST) handwritten recognition data set.     

Nanoscale domain switching in Bi3.15Eu0.85Ti3O12 thin films annealed at different temperature by scanning probe microscopy

The nanoscale domain switching behavior of Bi_3.15Eu_0.85Ti₃O₁₂ (BET) thin films annealed at temperatures of 600, 650 and 700 °C is investigated by scanning probe microscopy (SPM) via the direct observation on their domain structure. It is shown that most ferroelectric domains are clearly detectable and confined in the grains. Some domains opposite to the polarizing electric field were observed by SPM, and their formations are attributed to the grain boundaries playing an active roles in pinning a preferential polarization state. The remnant polarization (2P_r) values of BET thin films increase with the annealing temperature due to the increase of nanoscale domains switched into the direction of polarizing electric field.