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

技术概要：铁电体和铁弹性体（在其晶体结构中分别具有内置极化和弹性变形状态的材料）的功能特性通常依赖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。在梯度场作用下，铁磁现象的范围也很广，但受到的关注要少得多。该项目基于美国/乌克兰团队发起的两个新发现/想法：新的高度可调亚稳态和轮转柔版现象。在畴壁处和附近产生的强梯度场可以导致局部相变，导致在经典教科书铁电体中通常不期望的新的体极性相，甚至在非极性铁弹中。在所有氧化物界面与氧八面体倾斜，创建一个极化（高达1-10微C/cm 2）预测通过旋转致伸缩挠曲电产品的效果，可以显着影响界面电荷传输。使用光学二次谐波发生显微镜，拉曼显微镜，扫描探针显微镜，纳米级X射线衍射成像，z衬度扫描透射电子显微镜，分析理论，相场建模和第一原理理论，这个合作团队探索这些新现象。从广义上讲，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）重点发展理论框架。非技术性总结：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。界面处的梯度耦合可以导致下一代高速晶体管的极大电流感兴趣的二维电子气系统。该项目还开发了尖端的定量显微镜工具，并通过模拟挠曲电和其他梯度效应来推进理论建模。NSF奖提供资金，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长期访问，促进大学之间的互动（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-Ukraine），通过K-12支持外联活动，并为妇女和代表性不足的群体提供研究机会。该项目由电子和光子材料计划和材料研究部特别计划办公室支持。

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.