Discovery and Design with the FAST Principle: Following Local Models of Stability to Emergent Phenomena in Intermetallic Structures

NON-TECHNICAL SUMMARY: The role played by metallic materials in the advancement of prosperity and national security is evolving. Research in these materials has increasingly shifted from mechanical properties, conductivity, and corrosion resistance to more exotic effects related to the quantum nature of electrons, such as the resistance-free conduction of electric currents, advanced magnetic phenomena, and the conversion of thermal energy into electric energy.

Underlying these properties is a startling diversity in the geometrical arrangements that the atoms of materials can form at the microscopic level. Understanding and learning how to control these arrangements is a limiting factor in the design of new metallic materials. This project is promoting the progress of science by building a predictive model for how different types of interactions between neighboring atoms in a metal propagate to form the observed complex atomic arrangements, opening avenues to the discovery of new materials.

Theoretical calculations are being used to analyze these interactions and explore their implications, while databases of structural information are scanned to identify metallic materials in which intriguing behavior at the atomic level are expected. The predictions of theory are guiding experimental investigations of new metallic compounds, which provide feedback on the models being developed.

This project also impacts the training and education in the STEM fields, with an emphasis on solid state chemistry. New content is being created for the Science through Comics website, which uses relatable analogies and humor to inspire interest in science. In addition, the free on-line textbook Interactive Solid State Chemistry is being developed for dissemination to a broad range of students and educators in collaboration with LibreTexts.

Here, comics introducing the materials are integrated with interactive tools for active student engagement, such as structure models that can be manipulated in three dimensions. The research team is also increasing the participation of members of underrepresented groups in the sciences through outreach activities and mentoring.

TECHNICAL SUMMARY: Intermetallic phases are a rich source of potential functional materials, as they combine an unparalleled structural diversity with valuable physical properties. To fully realize this promise, however, design principles are still needed for guiding the crystal structures of these phases, such that their structure-properties relationships can by systematically investigated, and materials with structures tailored to specific applications can be prepared.

In this project, the need for such design principles is being addressed through the development of the predictive capabilities of the Frustrated and Allowed Structural Transitions (FAST) approach. Of the many transformations or modifications a structure could potentially undergo, those that involve cooperation between the various factors influencing stability can be expected to out-compete energetically those in which the factors conflict with each other.

In one component of this work, the scope of the FAST approach is being expanded through the computer-aided screening of crystal structure databases for geometrical features associated with easy transitions, yielding candidate structures for theoretical analysis and experimental investigation. Simultaneously, the completeness of the FAST picture is tested and improved through its application to the structural preferences involving 18-n+m isomerism in transition metal-main group intermetallics, in which a variety of bonding configurations are used by different compounds to adhere to the 18-n electron counting rule for any given electron count.

Finally, the predictive implications of the FAST schemes are explored by translating these pictures into force field models for large-scale molecular dynamics simulations. Predictions of emergent structural properties, such as incommensurate modulations or phase transitions, are pursued experimentally. In all of these endeavors, the experimental results are being used to refine the theoretical and conceptual approach.

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.