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

铁电材料具有可重定向(或？切换？)的固有极化。有一个外加的电场。了解缺陷、晶粒度和其他材料参数如何影响这一切换过程，对于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调焦的精密定位器等应用中的设备性能非常重要。这项EAPSI项目旨在通过收集电场诱导极化过程中具有广泛颗粒尺寸分布的钛酸钡陶瓷的时间分辨中子衍射数据来确定颗粒尺寸对铁电开关速度的影响。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约翰·丹尼尔斯博士合作进行。颗粒尺寸对铁电材料介电常数的影响是众所周知的，但对开关速度的影响尚不完全清楚。目前的假说认为，晶界介电常数与晶格介电常数的不同会导致局部电场增强，从而在晶界形成新的电畴。这一理论将通过在经历电场诱导极化时对具有广泛颗粒尺寸分布的钛酸钡样品进行的时间分辨、频闪中子衍射实验来探索。本征(压电)和非本征(非180°磁区切换)分量的应变贡献很容易分离，并且使用该技术能够收集铁电体感兴趣的时间尺度上的结构信息(1 S)。这些组合的信息将允许准确检测压电应变率和相关的铁电极化速度。这项工作将与澳大利亚核科学和技术组织的新南威尔士大学副教授John Daniels博士合作进行。该奖项由东亚和太平洋暑期学院项目资助一名美国研究生的夏季研究，由NSF和澳大利亚科学院联合资助。

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.