Confronting Complexity in Intermetallics: A Synthetic, Structural and Theoretical Approach

Cornell University, Ithaca NY

Investigators

Abstract

TECHNICAL EXPLANATION This project addresses the synthesis, structural characterization, properties, and band calculations for, are phases in which there are lattice mismatches between two metal structural motifs (noble metal gamma-brass superstructures), large cubic phases which can be decomposed into simpler components, phases composed of concentric icosahedral symmetry clusters, and structures composed of extended electron deficient clusters. All these systems lay near the metal-insulator boundary, some on one side, some on the other, have complex scaling properties, and potentially contain interfaces between their more metallic (covalent) and more ionic components. They test the boundaries of current paradigms useful for pure metals, insulators or semiconductors. Students working on this project will learn how to apply modern electronic structure calculations to understand the complex crystal structures that can now be obtained through modern synchrotron radiation diffraction experiments. NON-TECHNICAL EXPLANATION The classic alloys of civilization, brass and bronze, the elements, copper silver and gold lie at the heart of the proposed project. Our understanding today of their structures is remarkably still often imbedded in classical notions: the Platonic polyhedra for example. This project aims at a coherent structural reworking of these structures and the other structures derived from them. It will be a reworking from a classical geometrical picture (still used in understanding structures of gamma-brass for example), to paradigms based on simple quantum mechanical calculations. It is anticipated that the understanding will evolve into models based on minimal surfaces and interlocking intermeshed substructures. The materials being studied are chosen not just because they have hitherto proven difficult to understand but also because we think that such materials possess an unusual balance of bonding trends that could very well lead to materials with novel properties such as segregation between ionic and metallic components , and sub-lattice shear patterns, properties which affect the electrical and magnetic and cohesion properties of these essential alloys.