Chemical Pressure Scaffolding of Emergent Behavior in Intermetallic Phases

About This Grant

NON-TECHNICAL SUMMARY: Alloys and metals and play a central and evolving role in the progress of science, national prosperity, and national defense. While metals are best known for their traditional use as structural materials, well-defined combinations of them with fascinating and transformational properties continue to be discovered. Examples include the ability to conduct electricity without resistance, interconvert heat and electric energy, exert powerful magnetic forces, catalyze chemical reactions, and manifest the quantum nature of matter. A central factor in the emergence of such behaviors is the formation of intermetallic compounds, in which mixtures of atoms of different metals adopt specific geometries that are often unrecognizable compared to those of the pure elements. However, how these geometrical configurations determine the properties of a metallic material and how they can, in turn, be controlled remain critical questions. With this project, funded by the Solid State and Materials Chemistry program and the Condensed Matter and Materials program, both in NSF’s Division of Materials Research, Prof. Fredrickson and his research group is developing (1) principles that connect the properties of a material to patterns formed by the forces between its atoms, and (2) guidelines for how these forces can be harnessed in materials discovery. The implications of the devised principles are explored with the synthesis and characterization of new solid state compounds, as well as theoretical calculations. This project also contributes to the strengthening of the national STEM workforce through the training of new scientists and educational outreach. Content for the online resource “Interactive Solid State Chemistry” is being created, which merges comics and interactive web modules to teach concepts in solid state and materials chemistry. In addition, the project is enabling a traveling exhibit, “From Crystals to the Molecular World”, that uses the theme of crystallography to bridge hands-on experiences with rocks and minerals to the atomic-level structures of materials. TECHNICAL SUMMARY: Intermetallic phases represent a seemingly limitless source of potential structure-properties relationships, but the realization of this prospect is a daunting challenge. The diverse members of this class of solid state compounds encompass an incredible range in both structure and behavior. However, that very diversity—along with the intricate nature of their bonding and electronic structures—creates great difficulty in relating geometry and properties through either theoretical or empirical means. Net-based descriptions of structures have long formed a shared language for describing these two aspects of intermetallics: nets, or their 3D generalization as polyhedra, form a convenient way of communicating complex geometrical arrangements, while certain nets or patterns of atoms are sought after for predicted properties. In most cases, though, it remains challenging to divide a crystal structure into nets or other motifs from which materials behavior can be predicted. This project, with support from the Solid State and Materials Chemistry program and the Condensed Matter and Materials program, both in NSF’s Division of Materials Research, develops the chemical pressure (CP) scaffolding concept as a framework for directly associating specific periodic geometric patterns with materials properties. Networks of overly compressed interatomic interactions (positive CP) are hypothesized to form scaffolds for various types of soft atomic motions that underlie structural transformations or materials properties. This concept is being developed through the creation, testing, and refinement of (1) tools to compare CP scaffolds among crystal structures and connect them to properties, (2) synthetic strategies to modify the CP scaffolds within structures, and (3) approaches to investigate the interaction between CP scaffolds and electronic driving forces in materials behavior. The pursuit of these objectives tightly integrates theory and experiment, as well as use of graph-theory approaches to generalize the results into broad themes for intermetallic structures. 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.