Phase-field Modeling of Flexoelectric Contributions to Ferroelectricity

挠曲电对铁电贡献的相场建模

• 批准号: 1410714
• 负责人: Long-Qing Chen
• 金额: $ 31.5万
• 依托单位: Pennsylvania State Univ University Park
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2014
• 资助国家: 美国
• 起止时间: 2014-09-01 至 2018-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1410714&HistoricalAwards=false
• 关键词: Phase; field; Modeling; Flexoelectric; Contributions

NONTECHNICAL SUMMARYThis award supports theoretical research and computational modeling, and education with an aim to better understand ferroelectrics, which are multifunctional materials that have many uses, including actuators, sensors, memory storage, and microelectromechanical systems. These materials can not only produce electric signals under an applied electric field or a macroscopic shape deformation under an applied mechanical stress field but can also produce electric signals in response to an applied mechanical stress or a shape deformation in response to an applied electric field. There have been extensive studies on the couplings among electric signals, electric fields, homogeneous mechanical loads, temperature, and homogeneous shape deformations, and the basic science of how a homogeneous shape deformation affects the electric properties of ferroelectrics, characterized by the "piezoelectric effect," is reasonably well understood. In this project, the PI will focus on understanding how an inhomogeneous stress or shape deformation affects the multifunctional properties of ferroelectrics, through the "flexoelectric effect." Effort will be devoted to developing efficient computational methods and employing them to model, predict, and understand internal, nanoscale inhomogeneous structures and properties of ferroelectric materials under the influence of the flexoelectric effect. The computational research will be carried out in close collaboration with numerous experimental groups, computational physicists, and applied mathematicians. The fundamental understanding achieved and the computational tools developed in this project should provide guidance to develop material systems that can exploit the flexoelectric effect that exists in all materials. The proposed research is expected to contribute to graduate education in materials as phase-field simulations of phase transformations and microstructure evolution are being incorporated into graduate courses at Penn State. In particular, user-friendly graphical interfaces for a number of applications of the phase-field models have been developed under prior NSF support. The software has been employed in two graduate courses and one undergraduate course. In addition, it has been used in summer short courses on computational thermodynamics and kinetics of phase transformations, which were offered to research scientists from national labs, engineers from industry, and professors and students from academia. This project will provide new computational tools to illustrate how materials properties may be modified through the flexoelectric effect. The PI will involve undergraduate students in the research by participating in a number of programs at Penn State including senior thesis projects and the Minority Undergraduate Research Experience program.TECHNICAL SUMMARYFerroelectrics are a class of materials in which a spontaneous electric polarization develops below their paraelectric to ferroelectric phase transition temperatures. The spontaneous polarization direction can be reoriented among crystallographically defined orientations in a single crystal by an electric field. Very often a spontaneous strain arising from the crystal structure change at the ferroelectric transition accompanies the appearance of spontaneous polarization. So, the state of a ferroelectric crystal can generally be characterized macroscopically by two order parameters, polarization and strain. It is the coupling between the order parameters, polarization and strain, and the thermodynamic variables such as temperature, stress, and electric field that leads to the multifunctionality of a ferroelectric crystal ranging from dielectric, piezoelectric to pyroelectric properties, and thus to many applications in a wide variety of electronic devices, including capacitors, actuators, nonvolatile memories, and microelectromechanical systems. Although the thermodynamics of these couplings has been well established, the coupling among order parameters and their gradients is much less well understood. The main goal of this proposed program is to fundamentally understand the role of the flexoelectric effect, the coupling between polarization and the gradient of strain in the ferroelectricity of a crystal, in domain structures, polarization distributions across domain walls, and domain switching. There is sufficient evidence that the flexoelectric effect, which is small and generally ignored in macroscopic systems, may become significant or even dominant with decreasing size approaching nanostructures, particularly in ferroelectric materials which exhibit strong dielectric properties. The PI plans to employ a phase-field modeling approach integrated with mesoscale elasticity and electrostatic theory. The main objectives of this proposal are: (1) to develop a phase-field model of ferroelectric domain structures and switching incorporating flexoelectric contributions, (2) to study whether the flexoelectric contribution can significantly modify the properties of a ferroelectric domain wall and to discover potentially new domain wall features induced by the flexoelectric effect, (3) to investigate the role of the flexoelectric contribution to the polarization distribution and thus to domain structure in thin films, and (4) to investigate the flexoelectric response of ferroelectric thin films under a local mechanical force and explore the possibility of mechanical switching of ferroelectric polarization. The proposed research is expected to: (1) yield a phase-field formulation for modeling flexoelectric response of ferroelectrics, (2) significantly contribute to the fundamental understanding of the roles of flexoelectric effect in ferroelectric properties including domain wall structures, polarization distribution, and switching, and (3) produce advanced numerical algorithms based on the spectral method for solving phase-field equations involving domain wall anisotropy and flexoelectricity. The project will contribute to human resource development by training both graduate and undergraduate students through undergraduate thesis and summer research. The research findings will be disseminated to a wide audience through archival publications and conferences, review papers, and active participation and lectures at workshops and conferences. Finally, the PI will actively pursue collaborations with industry and national labs such as Los Alamos, Argonne, Oak Ridge, and the industrial members associated with the Center for Dielectrics and Piezoelectrics (CDP) at North Carolina State University and Penn State to provide internship opportunities for students involved in the project.

非技术摘要这一奖项支持理论研究和计算建模，并旨在更好地理解铁电的旨在，它们是具有多种用途的多功能材料，包括执行器，传感器，存储器存储和微电机电系统。这些材料不仅可以在施加的电场下产生电信号或在应用机械应力场下的宏观形状变形，而且还可以响应于施加的机械应力或形状变形而产生电信号。 关于电信号，电场，均匀的机械载荷，温度和均匀形状变形的耦合的广泛研究，以及均质形状变形如何影响铁电特性的基础科学，其特征是“ PiezoElectric效应”的特征。 在该项目中，PI将专注于理解不均匀的应力或形​​状变形如何通过“挠性效应”影响铁电的多功能特性。 努力将致力于开发有效的计算方法，并采用它们来建模，预测和理解内部纳米级的不均匀结构和铁电材料的性质，这是在挠性效应的影响下。计算研究将与众多实验组，计算物理学家和应用数学家密切合作。该项目中获得的基本理解以及在本项目中开发的计算工具应提供指导，以开发可以利用所有材料中存在的挠性效应的材料系统。预计拟议的研究将在材料中为研究生教育做出贡献，因为相变和微观结构演化的相位模拟已纳入宾夕法尼亚州立大学的研究生课程。 特别是，在先前的NSF支持下已经开发了用于相位模型的许多应用程序的用户友好图形接口。 该软件已在两个研究生课程和一门本科课程中使用。 此外，它已用于夏季简短的计算热力学和相转化动力学的简短课程，这些课程提供给了来自国家实验室，工业工程师以及学术界的教授和学生的研究科学家。 该项目将提供新的计算工具，以说明如何通过FlexoElectric效果修改材料属性。 PI将通过参加宾夕法尼亚州的许多计划，包括高级论文项目和少数群体的本科研究经验计划，使本科生参与研究。技术摘要是一类材料，在该材料中，自发的电力极化在其在副层面下在其对手降低到铁电相变温温度。 自发极化方向可以通过电场在单晶中的晶体定义方向之间进行重新定位。 经常是由晶体结构在铁电过渡时发生变化产生的自发应变，伴随自发极化的出现。因此，通常可以通过两个阶参数，极化和应变来宏观地表征铁电晶体的状态。 它是顺序参数，极化和应变之间的耦合，以及温度，压力和电场等热力学变量，导致铁电晶体的多功能性范围从介电，压电到Pyroelectric到Pyroelectric tos，以及许多应用程序，包括各种各样的电子录音机，包括电源元素，包括电源元素，包括电源元素，均不包括电源，并不是在范围。微机电系统。尽管这些耦合的热力学已经很好地确定，但订单参数及其梯度之间的耦合知之甚少。该提出的程序的主要目的是从根本上了解挠性效应的作用，晶体结构中晶体的铁电性中的极化和应变梯度之间的耦合，跨域壁的极化分布以及域切换。 有足够的证据表明，在宏观系统中且通常在宏观系统中忽略的柔性效应可能会随着尺寸降低接近纳米结构而变得显着甚至占主导地位，尤其是在表现出强介质特性的铁电材料中。 PI计划采用与中尺度弹性和静电理论集成的相位场建模方法。 该提案的主要目标是：（1）开发铁电域结构的相位模型和结合屈曲式贡献的切换，（2）研究是否可以显着改变铁电域壁的性能，并发现潜在的范围贡献的潜在贡献，从而引起了挠性和屈光度的贡献，并在（flexoelectrortric效应（3）中，（3）的贡献（3）因此，在薄膜中的结构域结构，（4）在局部机械力下研究铁电薄膜的挠性反应，并探讨铁电偏振机械切换的可能性。拟议的研究预计将：（1）产生一种相位的公式，用于建模铁电机的挠性反应，（2）显着有助于对挠性效应在铁运动特性中的作用的基本理解，包括域壁结构，偏置分布，开关以及（3）产生阶段 - 基于阶段的数字方法，以及（3）各向异性和柔韧性。 该项目将通过培训本科论文和夏季研究来培训研究生和本科生，从而为人力资源开发做出贡献。研究发现将通过档案出版物和会议，审查论文以及在研讨会和会议上的积极参与以及演讲来传播到广泛的受众。最后，PI将积极地与洛斯阿拉莫斯，阿尔莫斯，橡树岭等行业和国家实验室进行合作，以及与北卡罗来纳州立大学和宾夕法尼亚州立大学电介质和压电中心（CDP）相关的工业成员，以为参与该项目的学生提供实习机会。