Materials World Network: Gradient-Enabled Ferroic Phenomena: Tunable Metastable States, Roto-Flexo, and Transport Properties

技术概述：铁电体和铁弹性体的功能特性通常取决于它们在均匀空间弹性和电场下的响应，例如开关、压电和电光响应。铁电体和铁弹性体是晶体结构中分别具有内置极化和弹性畸变状态的材料。在梯度场下还会产生丰富的铁现象，但很少引起人们的注意。该项目基于美国/乌克兰团队提出的两个新发现/想法：新的高度可调亚稳态和旋转柔印现象。在畴壁和畴壁附近产生的强梯度场可能导致局部相变，从而导致在经典铁电材料中甚至在非极性铁弹性材料中通常无法预期的新的大块极性相。在所有具有氧八面体倾斜的氧化物界面中，通过旋转伸缩-挠曲电产物效应可以预测极化（高达1-10微c /cm2）的产生，该效应可以显著影响界面电荷输运。利用光学二次谐波生成显微镜、拉曼显微镜、扫描探针显微镜、纳米级x射线衍射成像、z-对比扫描透射电子显微镜、分析理论、相场建模和第一性原理理论，该合作团队探索了这些新现象。一般来说，美国团队（宾夕法尼亚州立大学，橡树岭国家实验室，阿贡国家实验室）进行实验研究并进行相场模拟，乌克兰团队（乌克兰国家科学院）专注于开发理论框架。非技术总结：该项目可能会导致新的高度可调，大压电响应无铅材料，用于精密运动和传感器。界面上的梯度耦合可以导致对下一代高速晶体管有很大兴趣的二维电子气体系统。该项目还开发了尖端的定量显微镜工具，并通过模拟柔性电和其他梯度效应来推进理论建模。国家科学基金会的奖金提供资金，以激励和维持一个国际研究团队，该团队于2007年开始。它资助本科生和研究生在全球范围内工作和合作，支持pi和学生跨越大西洋的扩展访问，进一步促进大学（宾夕法尼亚州立大学），国家实验室（橡树岭和阿贡）和国际合作者（nas -乌克兰）之间的互动，支持通过K-12的推广活动，并为妇女和代表性不足的群体提供研究机会。本项目由电子与光子材料项目和材料研究部特殊项目办公室支持。

TECHNICAL SUMMARY: The functional properties of ferroelectrics and ferroelastics, materials with built-in polarization and elastic distortion states in their crystal structure, respectively, are typically reliant on their response under uniform spatial elastic and electric fields, e.g., switching, piezoelectric, and electro-optic responses. There is also a rich range of ferroic phenomena arising under gradient fields, which receive much less attention. This project is based on two new discoveries/ideas initiated by the US/Ukraine team: New highly tunable metastable states and roto-flexo phenomena. Strong gradient fields created at and in the proximity of domain walls can result in local phase transitions that lead to new bulk polar phases not normally expected in classic textbook ferroelectrics, and even in non-polar ferroelastics. In all oxide interfaces with oxygen octahedral tilts, the creation of a polarization (up to 1-10 microC/cm2) is predicted through a rotostriction-flexoelectric product effect that can significantly impact the interface charge transport. Using optical second harmonic generation microscopy, Raman microscopy, scanning probe microscopy, nanoscale X-ray diffraction imaging, z-contrast scanning transmission electron microscopy, analytical theory, phase-field modeling, and first principles theory, this collaborative team explores these new phenomena. Broadly speaking, the US team (Pennsylvania State University, Oak Ridge National Labs, Argonne National Labs) conducts experimental research and performs phase-field simulations, and the Ukrainian team (National Academy of Sciences, Ukraine) focuses on developing the theoretical framework. NON-TECHNICAL SUMMARY: This project can potentially lead to new highly tunable, large piezoelectric response lead-free materials useful for precision motion and sensors. Gradient couplings at interfaces can lead to two-dimensional electron gas systems of great current interest for next generation high-speed transistors. This project also develops cutting-edge quantitative microscopy tools and advances theoretical modeling by simulating flexoelectric and other gradient effects. The NSF award provides funds to energize and sustain an international research team, which started in 2007. It funds undergraduate and graduate students to work and collaborate in a global context, supports extended visits across the Atlantic by PIs and students, furthers interactions between a university (Penn State), national labs (Oak Ridge and Argonne) and international collaborators (NAS-Ukraine), supports outreach activities through K-12, and provides research opportunities for women and underrepresented groups.This project is supported by the Electronic and Photonic Materials program and Office of Special Programs, Division of Materials Research.