CAREER: Overcoming the trade-off between thermopower and conductivity in transition metal oxides

人类产生的总能量中有近三分之二被浪费在热能上。面对日益增长的对气候变化的担忧，有效回收废热是一项紧迫的重大科学挑战。热电（TE）转换过程将废热转化为可用的电力，提供了一种有前途的清洁和可持续能源。该过程的效率取决于材料的固有性质，特别是热电性和导电性。然而，当前的氧化物材料系统和工程设计在实现有利的TE性质方面面临挑战。因此，发现具有良好TE特性的新材料以及利用它们的设计对于开发高性能TE器件至关重要。该项目的重点是过渡金属氧化物，由于其无毒，丰富和在高温下的稳定性，这是有前途的TE材料。本项目旨在建立一种新的方法，以实现大的热电势和高导电性的过渡金属氧化物。这种方法结合了一种新的氧化物异质结构与柱状微结构和垂直界面，沿着添加金属纳米颗粒。PI致力于提高公众对材料科学的关键作用的认识，并促进未来材料科学家和工程师的成长。为此，PI计划为高中学生和教师提供关于氧化物的讲座和科学演示。此外，还为人数不足的本科生和研究生提供实践研究培训和指导机会，激发他们对材料科学工程研究和相关职业的兴趣。技术说明为了满足对能够将废热转化为电能的高温TE器件日益增长的需求，必须发现具有大热功率和高电导率的过渡金属氧化物（TMO），从而能够实现相当大的功率因数。然而，由于增强导电性和热电性之间的固有权衡关系，实现同时具有两种性质的高值的TMO仍然是一个艰巨的挑战。该项目的总体目标是通过建立一种全新的方法来克服这种权衡，该方法结合了两种新兴策略：垂直应变和TMO独特的氧化还原缺陷化学。PI计划通过合成由两种不同钙钛矿组成的垂直排列的纳米复合材料，结合金属纳米颗粒的出溶，探索TMO中应变，氧化还原缺陷和TE性能之间的关系。在具有A位缺陷的钙钛矿材料中，金属出溶发生在还原过程中，导致能量过滤效应，从而增强热电性，同时保持导电性并使劣化最小。同时，通过最大化沿垂直取向的纳米复合材料中的垂直界面沿着拉伸应变，电子掺杂的钙钛矿中的氧空位的浓度显著增加，导致电导率的增强。在这个项目中获得的应变，氧化还原缺陷和TE性能之间的关系的基础知识提供了前所未有的设计自由度，并促进了氧化物TE材料的开发与上级性能。此外，该项目还得益于在国家实验室用户设施中使用尖端技术，从而提高了调查的精确度和深度。该项目中的创新方法可以作为一个多功能的建筑，能够容纳各种各样的功能特性，从而在广泛的能源和电子应用中取得进步，最终造福于公众。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Nontechnical DescriptionNearly two-thirds of the total energy generated by humanity is wasted as heat. In the face of growing concerns about climate change, efficient recycling of waste heat is an urgent significant scientific challenge. The thermoelectric (TE) conversion process transforms waste heat into usable electric power, providing a promising source of clean and sustainable energy. The efficiency of this process depends on the intrinsic properties of materials, particularly thermopower and electrical conductivity. Yet, current oxide material systems and engineering designs face challenges in achieving favorable TE properties. The discovery of new materials with good TE properties and designs to take advantage of them is therefore crucial for the development of high-performance TE devices. This project focuses on transition metal oxides, which are promising TE materials due to their non-toxic nature, abundance, and stability at high temperatures. This project aims to establish a novel approach for achieving large thermopower and high conductivity in transition metal oxides. This approach combines a new oxide heterostructure with columnar microstructures and vertical interfaces, along with the addition of metal nanoparticles. The PI is committed to elevating public awareness of the pivotal role of materials science and fostering the growth of future materials scientists and engineers. Towards this end, the PI plans to provide lectures and science demonstrations on oxides to high school students and teachers. Furthermore, hands-on research training and mentorship opportunities are provided for underrepresented undergraduate and graduate students to spark interest in materials science engineering studies and related careers.Technical DescriptionTo meet the growing demand for high-temperature TE devices capable of converting waste heat into electricity, it is indispensable to discover transition metal oxides (TMOs) with large thermopower and high electrical conductivity, enabling a substantial power factor. Nevertheless, due to the inherent trade-off relationship between enhancing conductivity and thermopower, achieving TMOs with simultaneously high values of both properties remains a formidable challenge. The overarching goal of this project is to overcome this trade-off by establishing a completely new approach that combines two emerging strategies: vertical strain and the unique redox defect chemistry of TMOs. The PI plans to explore the relationships between strain, redox defects, and TE properties in TMOs by synthesizing vertically aligned nanocomposites composed of two different perovskites through pulsed laser deposition in combination with the exsolution of metal nanoparticles. In perovskite materials with A-site deficiencies, metal exsolution occurs during reduction, leading to an energy filtering effect that enhances thermopower while preserving conductivity with minimal deterioration. Simultaneously, by maximizing tensile strain along the vertical interface in vertically aligned nanocomposites, the concentration of oxygen vacancies in electron-doped perovskites significantly increases, leading to an enhancement of conductivity. The fundamental knowledge gained on the relationships between strain, redox defects, and TE properties in this project provides unprecedented design freedom and facilitates the development of oxide TE materials with superior properties. In addition, this project benefits from the use of cutting-edge techniques in national laboratory user facilities, enhancing the precision and depth of the investigations. The innovative approach in this project can serve as a versatile architecture capable of accommodating a diverse array of functional properties, leading to advancements in a wide range of energy and electronic applications, ultimately benefiting the public.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.