LEAPS-MPS: Interrogating Negative Thermal Expansion in Earth-Abundant Oxide Materials

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

Thermal expansion, the way materials change shape when you heat or cool them, is an important property to be able to understand and control. Many objects that people rely on every day (i.e. building materials, aerospace parts, etc.) can wear out or fail more easily if their thermal expansion is not matched well, thus creating more waste and higher costs in the world.

While many materials expand as you heat them, some materials shrink as you heat them and are important to study. Therefore, it is important to understand how to control these properties so that new types of materials can be engineered. With this LEAPS-MPS project, Professor Joya Cooley at California State University, Fullerton, will focus on understanding why certain classes of materials which consist of earth-abundant elements shrink instead of expanding upon heating.

The research is conducted at a primarily undergraduate institution where undergraduate students will be trained in a variety of synthetic and characterization techniques. Specifically, students from historically underserved backgrounds will be recruited to work on this project and will disseminate findings to the public through local outreach, allowing participating students to serve as role models for future scientists from historically underserved backgrounds.

Furthermore, this local outreach will work to increase the amount of citizen science, public scientific literacy, and overall public interest in materials chemistry. Technical Summary

This LEAPS-MPS award is aimed at understanding structural and chemical driving forces that lead to technologically relevant negative thermal expansion (NTE) in materials. This work will interrogate local and long-range structure in materials crystallizing as metal pyrophosphates and pyrovanadates (A2B2O7) using inexpensive and readily accessible elements (e.g., A = Mg, Mn, Co, Ni, Cu; B = P, V).

The goal is to achieve the following: (1) investigate the role of A and B site elements and their influence on parent crystal structure; (2) understand the role of A and B site elements and their role in tuning temperature and range of NTE. The ability to vary metal (A) and nonmetal (B) identities in pyrophosphate (A2P2O7) and pyrovanadate (A2V2O7) materials by creating solid solutions provides a wealth of exploration possibilities for uncovering the structural drivers for NTE.

By creating solid solutions between end members with properties at the extremes, this work will seek to elucidate the structural and chemical variables important to O motion that results in systematic control of NTE. This project will make use of (a) high resolution structural techniques, such as synchrotron diffraction; (a) techniques sensitive to light elements like O, such as neutron diffraction; (c) and techniques that provide a local understanding of atom motion, such as temperature dependent microscopy.

Undergraduate students will be trained in solid-state chemistry techniques, including the opportunities to work with national laboratories for remote or hands-on experiments. Historically underserved students will be recruited to be part of this project and will engage in local outreach to increase public scientific interest and literacy.

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.