Perceiving Function in Geometrical Beauty: Chemical Pressure as a Link between Structure and Properties in Intermetallics

University Of Wisconsin-Madison, Madison WI

Investigators

Abstract

NON-TECHNICAL SUMMARY: Intermetallic phases are a class of metals and alloys that exhibit a vast range of materials behaviors valuable for technological applications. Examples include the catalysis of reactions for chemical synthesis or energy generation, the conversion of temperature gradients into electrical energy, the maintenance of strong and permanent magnetic moments, and the ability to recover an original geometry after drastic mechanical deformations. A pressing problem is relating these desirable behaviors to the often complex atomic arrangements within intermetallics, the solution to which could allow rational approaches to enhancing these properties. The focus of this research supported by the Solid State and Materials Chemistry (SSMC) program in the Division of Materials Research is the development of such connections between atomic arrangements and materials behavior for intermetallics. Theoretical methods are used to make predictions about atomic geometries within these compounds, the physical properties arising from these structures, and their responses to changes in pressure or temperature. Experiments involving the creation of new materials and the measurement of their properties are then used to test these predictions and revise the theoretical models. In addition, this project involves the development of resources for teaching solid state and materials chemistry, a subject typically underrepresented in the undergraduate curriculum. New content is being developed for the online textbook Interactive Solid State Chemistry, which harnesses the interactive capabilities of the webpage format to enhance students' experience of the material. This resource is available to a broad range of educators and students through its inclusion as a Living Textbook in the Chemical Education Digital Library, a pathway in the National Science Digital Library. Interest and awareness of materials chemistry is also promoted through the production of Science Through Comics, a website in which aspects of the field are illustrated in a non-technical and humorous way. TECHNICAL SUMMARY: Intermetallic phases comprise a broad family of solid state materials that are remarkable for both their structural diversity and rich range of physical properties. Intermetallics thus show great promise for materials design efforts, in which structural features are adjusted for the optimization of particular properties. A limiting factor in realizing this potential, however, is the need for clear relationships between their often complex atomic arrangements and the physical properties they exhibit. Under prior NSF support, a theoretical method was developed that offers a way of bridging these aspects of intermetallics: Chemical Pressure (CP) analysis. In this approach, the output of density functional theory (DFT) calculations is used to construct maps of the local pressures within solid state structures, which reveal how conflicts between electronic interactions and atomic packing constraints underlie a broad range of structural phenomena in metallic phases. In this project supported by the Solid State and Materials Chemistry (SSMC) program, the CP approach is built into a predictive conceptual framework that accounts not only for structural trends within intermetallics, but also their properties and phase transitions at high temperatures and pressures. The ultimate goal of this research is a unified understanding of structures and properties in intermetallics, which can be applied in materials design. Progress toward this aim is being achieved through three subprojects adapting the DFT-CP method to experimental design: (1) the synthetic exploration of new structural chemistry driven by CP relief, (2) the development and validation of principles connecting structure to vibrational properties, which in turn influence such physical properties as thermal stability, thermal conductivity, and superconductivity, and (3) the discovery of new pressure-induced structural transformations. The first subproject involves the synthesis in intermetallic systems motivated by CP calculations, the determination of newly encountered structures, and the use of data-mining and theory to place these structures into family trees whose branches represent pathways for CP release. The second and third subprojects leverage expertise and facilities available at the Advanced Photon Source at Argonne National Laboratory for Nuclear Resonant Inelastic X-ray Scattering (NRIXS) and high pressure synchrotron X-ray diffraction measurements, respectively, to verify the predictions of theory.