CAREER: Explore and Regulate Thermodynamics of f-block High Entropy Ceramics

该奖项全部或部分由2021年美国救援计划法案（公法117-2）资助。非技术摘要陶瓷是高熔点材料，用于从陶器到能源技术的许多应用中。一类新的陶瓷是高熵陶瓷（HEC），它是含有五种以上主要元素的多组分材料。 当这些元素是重原子时，HEC可以显示出独特的物理特性和高热稳定性，使其成为可持续能源和国家安全等一系列技术的保护涂层。 这个教师早期职业发展计划（CAREER）项目追求基础研究，为HEC的技术发展提供所需的知识。 HEC中一个突出的科学问题是结构中元素的随机性（与熵相关）及其键合（与能量相关）如何控制这些不同元素的混合，从而影响其高温性能？为了应对这一挑战，本研究的重点是确定HEC的热力学描述，以了解和预测其在现实世界中的应用行为。专门的仪器用于测量化学键的稳定性和强度，以及探测这些固体中原子的排列。该项目产生的预测模型将加速新HEC的材料发现。这个职业项目还旨在教育和激励科学，技术，工程和数学（STEM）领域的年轻人，从高中到本科和研究生。 教育活动包括让学生参与先进的实验和建模方法，为他们未来在STEM领域的职业做好准备。外联活动包括高中生暑期学校，以提高他们对陶瓷和热力学科学的科学兴趣。技术概述f-区HEC因其增强的稳定性、可调功能以及独特的化学和物理性质而受到越来越多的关注。然而，缺乏描述多种元素混合的结构和热力学模型显著阻碍了HEC的开发和设计。 主元素通常被假设为遵循随机分布（理想混合）。由于尺寸、电荷和共价性的差异，非理想混合可以增强双光子相互作用，但减弱熵贡献。对混合热力学的误解会导致对材料形成、有序-无序转变和相稳定性的不准确预测。这个CAREER项目的重点是发展各种4f和5 f元素在HEC中的混合效应及其对高温下热力学稳定性的影响的结构和热力学理解。该研究项目解决了三个知识差距，以实现HEC的准确热力学描述：i）对非理想双晶相互作用的有限理解，ii）构型熵的不准确估计，以及iii）高温下它们未知的温度依赖性。为了缩小这些差距，本研究从f区HEC开始，并追求两个协同目标：i）测量混合的热力学效应，并确定任何非理想热力学效应的起源和控制因素，以及ii）确定熵项并将其与焓关联，以获得f区HEC的完整热力学描述。这些结果将揭示在高温下相形成和转变的热力学驱动因素。外展活动为高中生提供了一个暑期研究机会，以加深他们对陶瓷和热力学科学的科学兴趣。教育部分包括先进的X射线光谱学本科生和研究生使用实验室为基础的光源，而不是同步加速器和先进的陶瓷热力学建模到研究生课程的整合。这个奖项反映了NSF的法定使命，并已被认为是值得通过评估使用基金会的智力价值和更广泛的影响审查标准的支持。

This award is funded in whole or in part under the American Rescue Plan Act of 2021 (Public Law 117-2).Non-Technical SummaryCeramics are high melting temperature materials used in many applications from pottery to energy technology. A new class of ceramics are high entropy ceramics (HECs), which are multicomponent materials containing more than five principal elements. When those elements are heavy atoms, HECs can show unique physical properties and high thermal stability, making them promising materials as a protective coating for a range of technologies such as sustainable energy and national security. This Faculty Early Career Development Program (CAREER) project pursues fundamental research to provide the needed knowledge for the technical development of HECs. An outstanding scientific problem in HECs is how do the randomness of elements in the structure (related to entropy) and their bonding (related to energy) control the mixing of these different elements and thereby affect their high-temperature performance? To address this challenge, this research focuses on determining thermodynamic descriptions of HECs to understand and predict their behavior in real-world applications. Specialized instrumentations are used to measure the stability and strength of chemical bonds as well as probe the arrangement of atoms in these solids. The predictive models generated from this project should accelerate materials discovery of new HECs. This CAREER project also aims to educate and inspire younger people in science, technology, engineering, and mathematics (STEM) fields, from high school to undergraduate and graduate students. The education activities include engaging students in advanced experimental and modeling methods that prepares them for future professions in STEM fields. Outreach activities include summer schools for high school students to increase their scientific interests in ceramic and thermodynamic sciences. Technical SummaryThe f-block HECs are gaining increased attention for their enhanced stabilities, tunable functions, and unique chemical and physical properties. However, the lack of structural and thermodynamic models that describe the mixing of multiple elements significantly impedes the development and design of HECs. Principal elements are often assumed to follow a random distribution (ideal mixing). Due to the differences in size, charge, and covalency, non-ideal mixing can enhance enthalpic interactions but attenuate entropic contributions. Misinterpretation of thermodynamics of mixing can lead to an inaccurate prediction of material formation, order-disorder transition, and phase stability. This CAREER project focuses on developing a structural and thermodynamic understanding of the mixing effects of various 4f and 5f elements in HECs and their impacts on thermodynamic stability under high temperatures. This research project addresses three knowledge gaps to achieve accurate thermodynamic descriptions of HECs: i) the limited understanding of non-ideal enthalpic interaction, ii) the inaccurate estimation of configurational entropy, and iii) their unknown temperature-dependencies under high temperatures. To close these gaps, this research begins with f-block HECs and pursues two synergistic objectives: i) to measure the enthalpic effects of mixing and determine the origins and controlling factors of any non-ideal thermodynamic effects, and ii) to determine and correlate entropic terms with enthalpy for a complete thermodynamic description of f-block HECs. These results will reveal the thermodynamic drivers for phase formation and transformation at elevated temperatures. The outreach activities feature a summer research opportunity for high school students to deepen their scientific interests in ceramic and thermodynamic sciences. The educational component includes advanced X-ray spectroscopy to undergraduate and graduate students using a lab-based light source instead of a synchrotron and the integration of advanced ceramic thermodynamics modeling into the graduate curriculum.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.