EAPSI: Determining Grain Size Effects on Ferroelectric Switching Speed by Time-Resolved Neutron Diffraction Measurements

铁电材料具有固有的极化，可以重新取向（或？转换？）施加电场。 了解缺陷、晶粒尺寸和其他材料参数如何影响这一切换过程，对于能够提高消费电子产品中的电容器、汽车碰撞检测系统中的惯性传感器或用于相机对焦的精确定位器等应用中的器件性能非常重要。 这个EAPSI项目旨在通过收集钛酸钡陶瓷的时间分辨中子衍射数据，确定晶粒尺寸对铁电开关速度的影响，钛酸钡陶瓷在电场诱导极化过程中具有广泛的晶粒尺寸分布。 这项工作将与澳大利亚核科学与技术组织的新南威尔士大学副教授John Daniels博士合作进行，他帮助开创了这种时间分辨衍射技术。晶粒尺寸对铁电体介电常数大小的影响是众所周知的，但对开关速度的影响尚未完全了解。 目前的假说声称，新的域形成在晶界处，由于局部电场增强引起的晶界和晶格之间的介电常数的差异。 这一理论将探讨通过时间分辨，频闪中子衍射实验钛酸钡样品进行了广泛的晶粒尺寸分布，同时进行电场诱导极化。 来自本征（压电）和非本征（非180°畴切换）分量的应变贡献很容易分离，并且利用该技术收集铁电体感兴趣的时间尺度（1 s）上的结构信息的能力。 这些组合的信息片段将允许精确检测压电应变速率和相关的铁电极化速度。 这项工作将与澳大利亚核科学技术组织的新南威尔士大学副教授John Daniels博士合作进行，他帮助开创了这种时间分辨衍射技术。该奖项属于东亚和太平洋夏季研究所计划，支持美国研究生的夏季研究，由NSF和澳大利亚科学院共同资助。

Ferroelectric materials possess an inherent polarization that can be reoriented (or ?switched?) with an applied electric field. Understanding how defects, grain size, and other material parameters affect this switching process is important to be able to improve device performance in applications such as capacitors in consumer electronics, inertial sensors such as those in automotive collision detection systems, or precise positioners used for camera focusing. This EAPSI project seeks to identify the effects that grain size has on ferroelectric switching speed by collecting time-resolved neutron diffraction data on barium titanate ceramics with a broad distribution of grain sizes during electric-field-induced polarization. This work will be conducted in collaboration with Dr. John Daniels, an Associate Professor at the University of New South Wales who helped pioneer this time-resolved diffraction technique, at the Australian Nuclear Science and Technology Organization.The effect of grain size on the magnitude of dielectric permittivity of ferroelectrics is well known, but the effects on switching speeds are not yet completely understood. Current hypotheses claim that new domains form at grain boundaries due to local electric field enhancements caused by a difference in permittivity between the grain boundary and the lattice. This theory will be explored via time-resolved, stroboscopic neutron diffraction experiments performed on barium titanate samples with a broad range of grain size distributions while undergoing electric-field-induced polarization. Strain contributions from intrinsic (piezoelectric) and extrinsic (non-180° domain switching) components are easily separable and the ability to collect structural information on time scales of interest to ferroelectrics (1 s) with this technique. These combined pieces of information will allow for accurate detection of piezoelectric strain rate and the associated ferroelectric polarization speeds. This work will be conducted in collaboration with Dr. John Daniels, an Associate Professor at the University of New South Wales who helped pioneer this time-resolved diffraction technique, at the Australian Nuclear Science and Technology Organization.This award under the East Asia and Pacific Summer Institutes program supports summer research by a U.S. graduate student and is jointly funded by NSF and the Australia Academy of Science.