Controlling the Behavior of Ferroelectric Materials through Strain Engineering

社会和工业越来越需要新材料来实现新的能力和新的应用。在其用途和技术影响方面正在增长的一类材料的一个例子是铁电材料。这些材料在受力(即压缩或弯曲时)时会产生电压或电流，反之亦然，当施加电压时，它们会产生运动。铁电材料已经被广泛地应用于从定位系统(例如，原子力显微镜上的尖端的移动)到能量收集(例如，在行走时从鞋子产生电流)。该项目将探索通过开发新材料来控制铁电材料的行为和性能的新方法，这种新材料在这里被称为挠性电材料，这种材料是铁电的，使用现代材料沉积方法制成的材料具有不同数量的原子能级应变(即变形)。换句话说，通过以一种非常可控的方式沉积材料，材料中原子之间的正常距离可以以所需的方式改变，这种原子偏离正常平衡的位移将导致材料性质的变化。该项目将培养能够在多学科团队环境中发挥作用的下一代科学家和工程师，并将广泛加强美国的基础设施，因为它涉及复杂材料的合成和制造。该项目还将利用旨在扩大未被充分代表的少数民族在科学和工程领域的参与的教育和外联计划。该项目的目标是开发关于如何产生不均匀应变(如应变梯度)并将其用于控制挠性电材料的新见解。特别是，将制定科学框架，利用现代薄膜沉积和加工路线，扩大对挠曲电效应(应变梯度和电极化之间的耦合)的基本了解和利用。该项目将通过结合材料的设计、合成、加工和表征来探索铁电材料中挠性电的性质和极限。将开发原位和非原位加工方法，通过制备柔性和独立的铁电薄膜来产生大的、可调的非均匀应变(即应变梯度)。该程序将回答两个核心问题：1)如何产生大的和确定的应变梯度；2)大应变梯度的存在如何影响铁电材料的场、应力和温度敏感性？将探索通过产生成分和缺陷梯度来原位合成薄膜中的大应变梯度。将探索在衬底支持的材料中产生大应变梯度的非原位制造和加工方法，以及释放和独立版本的材料，以及具有大应变梯度的材料的性能的演变。这项工作将影响铁电材料领域，包括基于铁电的特性，并将对使用铁电材料的设备产生直接影响，包括存储器和逻辑、传感器和执行器、热和能量转换应用。

Society and industry are increasingly calling upon novel materials to enable new capabilities and new applications. One example of a class of materials that is growing in terms of its use and technological impact are ferroelectric materials. These materials can produce a voltage or electric current when subjected to force (i.e., when compressed or bent) or vice-versa, they can produce movement when a voltage is applied to them. Ferroelectric materials are already utilized in a wide array of applications ranging from positioning systems (e.g., movement of the tips on atomic force microscopes) to energy harvesting (e.g., producing electric current from shoes during walking). This project will explore new ways to control the behavior and properties of ferroelectric materials by developing new materials, referred to here as flexoelectric materials, that are ferroelectric and that are made using modern material deposition methods which produce materials that have varying amounts of atomic level strain (i.e., deformation) built into them. In other words, by depositing the materials in a very controlled way, the normal distances between atoms in the material can be changed in a desired way and this displacement of atoms from their normal equilibrium will result in changes in the material properties. The project will train the next generation of scientists and engineers who can function in a multi-disciplinary team environment and will broadly enhance the infrastructure in the United States as it pertains to the synthesis and fabrication of complex materials. The project will also utilize education and outreach programs that are designed to broaden the participation of underrepresented minorities in science and engineering. The goal of the project is to develop new insights into how inhomogeneous strains (such as strain gradients) can be produced and used to control flexoelectric materials. In particular, scientific framework will be developed to utilize modern thin-film deposition and processing routes to expand the fundamental understanding and utilization of flexoelectric effects (the coupling between a strain gradient and electric polarization). The project will explore the nature and limits of flexoelectricity in ferroelectrics by combining design, synthesis, processing, and characterization of materials. In situ and ex situ processing methodologies will be developed to produce large and tunable inhomogeneous strains (i.e., strain gradients) via the fabrication of flexible and free-standing ferroelectric films. The program will answer two central questions: 1) how can large and deterministic strain gradients be produced, and 2) how does the presence of a large strain gradient impact the field, stress, and temperature susceptibilities of a ferroelectric material? In situ synthesis of large strain gradients in films via the production of compositional and defect gradients will be explored. Ex situ fabrication and processing methods to produce large strain gradients in substrate-supported materials will be explored, together with released and free-standing versions of materials, and the evolution of properties in materials with large strain gradients. This work will impact the fields of ferroic materials, including ferroelectric-based properties, and will have has direct impact on devices that utilize ferroelectrics including memory and logic, sensors and actuators, thermal and energy conversion applications.