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

该奖项的全部或部分资金来自《2021年美国救援计划法案》(公法117-2)。非技术概述陶瓷是一种高温材料，用于从陶器到能源技术的许多应用中。一类新的陶瓷材料是高熵陶瓷(HECS)，它是一种含有五种以上主量元素的多元材料。当这些元素是重原子时，HECS可以显示出独特的物理性质和高度的热稳定性，使它们成为一种很有前途的材料，作为可持续能源和国家安全等一系列技术的保护层。该学院早期职业发展计划(CALEAR)项目致力于基础研究，为HECS的技术发展提供必要的知识。HECS中一个突出的科学问题是，结构中元素的随机性(与熵有关)和它们的成键(与能量有关)如何控制这些不同元素的混合，从而影响它们的高温性能？为了应对这一挑战，本研究集中于确定HECS的热力学描述，以了解和预测它们在现实世界应用中的行为。专门的仪器被用来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。这个项目产生的预测模型应该会加速新HEC的材料发现。该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，从高中到本科生和研究生。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领域的职业做准备。外展活动包括为高中生开设暑期学校，以提高他们对陶瓷和热力学科学的科学兴趣。技术概述F-BLOCK HEC因其增强的稳定性、可调功能和独特的化学和物理特性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严重阻碍了HECS的开发和设计。通常假定主成分服从随机分布(理想混合)。由于大小、电荷和共价性的不同，非理想混合可以增强焓相互作用，但减弱了熵贡献。对混合热力学的误解可能导致对物质形成、有序-无序转变和相稳定性的不准确预测。这一职业项目侧重于发展对HECS中各种4f和5f元素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方面的理解。这项研究项目解决了三个知识空白，以实现对HECS的准确热力学描述：i)对非理想焓相互作用的有限理解，ii)构型熵的不准确估计，以及iii)它们在高温下未知的温度依赖关系。为了缩小这些差距，这项研究从f-块HECS开始，追求两个协同目标：i)测量混合的热效应，并确定任何非理想热力学效应的来源和控制因素；ii)确定和关联熵项和热焓，以完整地描述f-块HECS。这些结果将揭示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。教育部分包括使用实验室光源而不是同步加速器向本科生和研究生提供先进的X射线光谱分析，并将先进的陶瓷热力学建模整合到研究生课程中。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

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.