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

This award is funded in whole or in part under the American Rescue Plan Act of 2021 (Public Law 117-2). Non-Technical Summary

Ceramics 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 Summary

The 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.