Restricting Ferroelectric Domain Wall Motion with Volume Defects--Nanoprecipitates

非技术描述：压电陶瓷是一种功能材料，当受到机械力时会产生电荷，当受到电场时会改变其尺寸。这种机械和电气形式之间的能量转换可以具有极高的效率（高达90%）;因此，这些陶瓷在声纳，医学成像和无损评估等关键技术中具有广泛的应用。目前，控制和改善其功能特性的技术是在陶瓷中引入杂质原子。然而，这种技术已经达到了它的基本极限。目前的项目探索了一种全新的机制-将高度分散的杂质纳米晶体（~50 nm）引入块状陶瓷-以进一步提高压电陶瓷的性能，并使其能够在更高的温度和更高的电场下发挥作用。这些改进的陶瓷可用于制造在更极端条件下工作的下一代高功率器件。除了技术贡献外，该项目还为许多社区提供学习和职业发展机会。研究生和本科生，其中许多人来自代表性不足的群体，都参与了这个项目;研究陶瓷科学的毕业生通常可以在国家实验室和微电子和制造业的工业部门找到工作;并为K-12学生提供压电技术的各种演示，以鼓励科学思维并激发对科学和工程领域的兴趣。技术规格：本计画旨在建立一种借由奈米级共格沉淀物来稳定压电陶瓷之电畴结构及强化压电陶瓷之新机制。与最先进的点缺陷技术相比，体积缺陷提供了更强的限制，并且在更高的温度下是稳定的。因此，该项目有助于实现可以在更高的驱动频率和振动速度下使用的大功率压电换能器。作为一个模型系统，该项目的重点是无铅钛酸钡/钛酸钡组合物，在相图中的倾斜固溶线指导均匀分散的纳米级相干晶体在大块多晶陶瓷沉淀。据推测，富含CaTiO 3的沉淀物在大于临界尺寸时保持非极性，而在低于临界尺寸时变为极性。假设富含BaTiO 3的基质中的铁电畴壁受到不同尺寸沉淀物的不同模式限制。使用原位加热和偏压以及其他先进的透射电子显微镜技术直接验证了这些假设。研究生和本科生都参与了这个项目，并接受了陶瓷制造和性能表征的培训。该博士生将进一步接受尖端透射电子显微镜技术的培训，该技术用于在原子水平上表征沉淀物/基质界面的化学、位移、应变和电荷。该奖项反映了NSF的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。

NON-TECHNICAL DESCRIPTION: Piezoelectric ceramics are functional materials that develop electric charges when subjected to mechanical forces and change their dimensions when subjected to electric fields. Such conversion of energies between mechanical and electric forms can have extremely high efficiency (up to 90%); and hence, these ceramics have widespread applications in critical technologies such as SONAR, medical imaging, and non-destructive evaluation. Currently, the technique to manipulate and improve their functional properties is to introduce impurity atoms in the ceramic. However, this technique has reached its fundamental limit. The current project explores a radically new mechanism -- introducing highly dispersed impurity nanocrystals (~50 nm) into the bulk ceramic -- to further improve the performance of piezoelectric ceramics and allow them to function at higher temperatures and under higher electric fields. These improved ceramics can then be used to create next generation high-power devices that operate under more extreme conditions. In addition to technical contributions, this project also provides learning and career advancement opportunities for many communities. Both graduate and undergraduate students, many of whom from underrepresented groups, are involved in this project; graduates who study ceramics science can typically find employment in national labs and industry sectors of microelectronics and manufacturing; and various demonstrations on piezoelectric technologies are given to K-12 students to encourage scientific thinking and spark interest in science and engineering fields. TECHNICAL DETAILS: This project aims to establish a novel mechanism of stabilizing the domain structure and hardening piezoelectric ceramics with nanoscale coherent precipitates. Compared to the state-of-the-art point-defect technique, volume defects provide stronger restrictions and are stable under higher temperatures. Therefore, this project helps realize high-power piezoelectric transducers that can be used at higher driving frequencies and vibration velocities. As a model system, this project focuses on lead-free BaTiO3/CaTiO3 compositions, where slanted solvus lines in the phase diagram guide the precipitation of uniformly dispersed nanoscale coherent crystals in bulk polycrystalline ceramics. Presumably, the CaTiO3-rich precipitate remains non-polar when it is larger than a critical size and becomes polar when it is below the critical size. The ferroelectric domain wall in the BaTiO3-rich matrix is hypothesized to be restricted in different modes by precipitates of different sizes. The hypotheses are directly verified using the in-situ heating and biasing, and other advanced transmission electron microscopy techniques. Both graduate and undergraduate students are involved in this project and are trained with ceramic manufacturing and property characterization. The doctoral student is further trained with cutting-edge transmission electron microscopy techniques, which are used to characterize precipitate/matrix interfaces at the atomic level in terms of chemistry, displacement, strain, and charge.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.