Investigation of the ferroelectric domain dynamics and its effects on macroscopic behaviors using a synchrotron X-ray photon correlation spectroscopy

非技术领域的SUMMARY铁电(FE)材料表现出可通过电场转换的自发极化。这些材料由磁区组成，也就是极化方向相同的区域。铁材料已被用于各种电子设备，如红外传感器、致动器和超声换能器。虽然人们已经认识到，改变磁区结构可以提高FE材料的机电和介电性能，但对于什么是理想磁区大小或磁区壁密度(即相邻磁区之间的边界区域)以优化宏观材料性能，还存在一个知识缺口。本研究旨在开发一种基于X射线光子相关光谱(XPCS)的原位表征方法。XPCS可以在从毫秒到数百秒的时间范围内(从1微米到几十微米)研究材料原子结构的动力学。这一范围对解释原子现象对宏观行为的影响至关重要，目前的X射线衍射和压电响应力显微镜等现有技术无法有效地实现这一范围。新提出的方法比较了在外加电场作用下X射线图像的移位。将对位移程度进行统计分析，以揭示材料中机电响应的机制，包括通过连续的磁区变形或离散的磁区壁运动。这项研究的结果将是上述方法的可行性的概念证明，以进一步研究磁区壁密度和磁区大小对有限元材料性能的影响。此外，该提案还包括旨在促进代表人数不足的少数族裔群体从事STEM职业的教育计划。这些计划包括K-12外展计划，为大学生整合STEM课程，以及为URM小组的高中生和大学生提供研究指导。技术总结拟议的研究旨在通过概念验证研究区分与机电(即，压电)响应的内在(即，结构域扩展和偶极旋转)和外部(即，离散的结构域壁运动)贡献相关的X射线散射行为，来研究铁电(FE)结构域工程背后的基本机制。X射线光子相关谱(XPCS)提供了一种全新的方法来研究介观(一到几十微米)范围内的磁区和磁区壁效应，这是一个解释原子现象对宏观材料行为影响的临界长度尺度。相比之下，现有的基于X射线衍射的技术可以通过使用相应衍射峰的相对强度来估计宏观尺度上的磁畴转变。此外，理论估计仅限于可以由计算中使用的衍射峰完美地描述的磁区构型。类似地，虽然压电响应力显微镜可以直观地显示FE磁区图案，但由于扫描速度的限制，很难在介观尺度上表征原子结构的动态变化。相比之下，XPCS在一帧中获取散射信号，以跟踪在毫秒到数百秒内所有位置的模式漂移。本项目将使用PbTiO3-PbTiO3单晶来测试XPCS解相关函数的统计分布是否能够区分本征响应和外在响应的影响。我们的目标是开发一种‘双场’XPCS方法和一种统计分析工具，用于评估本征和外在机制对压电和介电性能的贡献。该项目还旨在通过涉及材料科学、X射线表征和数据科学的多学科研究来培养下一代工程师和科学家。研究成果还将用于教育K-12、本科生和研究生，通过各种倡议，如外展活动和创新的课程努力，来自代表性较低的少数群体。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

NON-TECHNICAL SUMMARYFerroelectric (FE) materials show spontaneous polarization that can be switched by an electric field. These materials consist of domains, the regions where the polarization is oriented in the same directions. FE materials have been used in various electronic devices such as infrared sensors, actuators, and ultrasound transducers. While it is well recognized that the modification of the domain configurations can enhance the electromechanical and dielectric properties of the FE materials, there is a knowledge gap regarding what is the ideal domain size or domain wall density (i.e., boundary regions between adjacent domains) to optimize the macroscopic material properties. The proposed research aims to develop an in-situ characterization method based on the X-ray photon correlation spectroscopy (XPCS). XPCS can investigate the dynamics of the atomic structures of materials over a range of time from milliseconds to hundreds of seconds in the mesoscale length (1 to tens of micrometers). This range is a critical to explaining the effect of atomistic phenomena on the macroscopic behavior and not efficiently accessible by the current existing techniques, such as X-ray diffraction and piezoresponse force microscopy. The newly proposed method compares the shift of X-ray images under applied electric field. The degree of shift will be statistically analyzed to reveal the mechanisms for electromechanical response in the material, including through continuous domain deformation or discrete domain wall motion. The outcome of this research will be a proof-of-concept of the viability of the above approach for further investigations of the effects of domain wall density and domain size on the FE material properties. Additionally, this proposal includes educational plans aimed at promoting STEM careers among underrepresented minority (URM) groups. These plans involve K-12 outreach initiatives, integrating STEM curriculum for university students, and providing research mentorship to high school and college students from URM groups.TECHNICAL SUMMARYThe proposed research aims to investigate the fundamental mechanisms behind the ferroelectric (FE) domain engineering through proof-of-concept research distinguishing X-ray scattering behaviors associated with the intrinsic (i.e., domain extension and dipole rotation) and extrinsic (i.e., discrete domain wall motion) contributions to the electromechanical (i.e., piezoelectric) response. The proposed approach by X-ray photon correlation spectroscopy (XPCS) provides a fundamentally new method to investigate the domain and domain wall effects in the mesoscopic (one to tens of microns) range, which is a critical length scale explaining the effect of atomistic phenomena on the macroscopic material behavior. For comparison, the existing techniques based on X-ray diffraction can estimate domain switching on a macroscopic scale, by using the relative intensity of the corresponding diffraction peak. Furthermore, the theoretical estimation is limited to the domain configuration that can be perfectly described by the diffraction peaks used in the calculation. Similarly, while piezoresponse force microscopy can visualize FE domain patterns, it is difficult to characterize the dynamic atomic structure changes at the mesoscale, due to the scanning speed limitations. In contrast, XPCS acquires the scattering signals in a frame to track the pattern shift in all locations over milliseconds to hundreds of seconds. This project will use Pb(Mg1/3Nb2/3)O3-PbTiO3 single crystals to test if the statistical distributions of the XPCS decorrelation functions can distinguish between the effects of intrinsic and extrinsic responses. The goal is to develop a 'two-field' XPCS method and a statistical analysis tool for assessing the contributions of intrinsic and extrinsic mechanisms to the piezoelectric and dielectric properties. This project also aims to educate the next generation of engineers and scientists through multidisciplinary research involving materials science, X-ray characterization, and data science. The research outcome will be also used to educate K-12, undergraduate, as well as graduate-level students from underrepresented minority groups through various initiatives, such as outreach activities and innovative curricular efforts.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.