EAPSI: In situ Structural Characterization of Lead-free, Bismuth-based Piezoelectric Thin Films

迫切需要发现和了解所有应用中铅基材料的环境友好、无毒和可持续替代品的行为（如铅基油漆和焊料）。对于压电材料（那些随着施加的电场而改变形状的材料，反之亦然）来说，合适的替代品尚未实现，这些压电材料对于大范围的设备和应用是重要的，例如致动器、加速度计、滤波器、振动控制、燃料喷射、喷墨打印、超声生成和感测以及谐振器。一类显示出作为替代品的巨大前景的材料是基于钛酸铋钠（BNT）。在用于微电子应用的薄膜中，这些新材料中的基本压电效应尚未被充分理解，以允许设备可靠地实现。因此，本项目的目标是探索与BNT基压电薄膜中的压电性相关的机制，使用东京工业大学Hiroshi Funakubo教授实验室提供的新颖表征方法。Funakubo教授的表征工具允许在施加电场的同时测量原子结构，从而直接洞察这些特殊材料的压电应变机制。这些BNT基材料在块状形式下属于称为弛豫铁电体的一类材料，其在电场诱导位移机制方面表现出诱人的特性，这一点刚刚开始被理解。许多基于BNT的组合物显示出应变和极化行为，这是可逆场诱导弛豫到铁电相变的特征;这些被称为遍历弛豫。然而，薄膜实施例中的基于BNT的材料没有表现出在块体中发现的增强的性质。特别是，已经在薄膜中研究的各态历经弛豫组合物没有显示出可逆场致弛豫到铁电相变的迹象，而是表现出与正常铁电体相似的行为，并且具有相对低的位移。这种不同的反应之间的散装和薄膜需要了解这种有前途的材料系统是可行的现实世界的应用。因此，新颖的原位微结构表征方法（二维X射线衍射和拉曼光谱），可在主办机构获得，将应用于阐明电场诱导应变机制BNT-该奖项是东亚和太平洋夏季研究所计划下的一个奖项，支持美国研究生的夏季研究，由NSF和日本促进发展协会共同资助。科学

There is a pressing need to discover and understand the behavior of environmentally benign, non-toxic, and sustainable replacements for lead-based materials in all applications (as already has been done for lead-based paints and solders). Suitable replacements have yet to be realized for piezoelectric materials (those that change shape with applied electric field and vice versa) that are important for a large range of devices and applications, such as actuators, accelerometers, filters, vibration control, fuel injection, ink jet printing, ultrasound generation and sensing, and resonators. One class of materials that shows great promise as replacements is based on bismuth sodium titanate (BNT). In thin films for microelectronic applications, the fundamental piezoelectric effect in these new materials is not yet understood well enough to allow devices to be reliably implemented. Accordingly, the objective of this project is to explore the mechanisms associated with piezoelectricity in BNT-based piezoelectric thin films using novel characterization methods available at Professor Hiroshi Funakubo's laboratory at the Tokyo Institute of Technology. Professor Funakubo's characterization tools allow for the measurement of atomic structure while applying electric fields, giving direct insight into the piezoelectric strain mechanisms of these exceptional materials.In bulk form, these BNT-based materials belong to a class of materials called relaxor ferroelectrics, which show enticing properties with regards to electric field induced displacement mechanisms that are just beginning to be understood. Many BNT-based compositions show the strain and polarization behavior that is characteristic of a reversible field-induced relaxor-to-ferroelectric phase transition; these are known as ergodic relaxors. However, BNT-based materials in thin film embodiments do not exhibit the enhanced properties that are found in the bulk. In particular, the ergodic relaxor compositions that have been studied in thin films do not show the signs of a reversible field-induced relaxor-to-ferroelectric phase transition, but rather behave similar to normal ferroelectrics and have comparatively low displacements. This differing response between bulk and thin films needs to be understood for this promising material system to be viable for real-world applications. Therefore, novel in situ microstructural characterization methods (2D X-ray diffraction and Raman spectroscopy), available at the host institution, will be applied to elucidate the electric field induced strain mechanisms in BNT-based piezoelectric thin films.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 Japan Society for the Promotion of Science.