Synthetic and structural studies are continuously revealing intermetallic phases to be a domain of unparalleled structural complexity and diversity. The rate at which this diversity is expanding far exceeds that of the development of theoretical models capable of accounting for and making predictions regarding this structural chemistry. The absence of such models is a bottleneck in the design of new intermetallic and alloy materials with tailored structures. A common theme can be perceived in the results of recent theoretical and experimental studies on complex intermetallic phases that may serve as the basis for a more comprehensive theoretical framework. Structural complexity in these phases can often be traced to a competition between or coexistence of mutually exclusive bonding or geometrical packing modes, a tension referred to here as "chemical frustration", by analogy with the phenomenon of magnetic frustration. Under the support of the SSMC/DMR program, this project aims to develop this concept through the examination of intermetallic systems designed to contain inherent tensions between variants on simple close-packing (SCP) and tetrahedra-based packing (TCP). Intermetallic systems will be studied with solid state synthesis aimed at the discovery of new phases, the structural analysis of these new phases, and electronic structure calculations. The theoretical efforts will include the development of theoretical tools designed for the detection and analysis of competing chemical bonding types. These theoretical tools will be based on the Moments Method applied to Hückel calculations calibrated against Density Functional Theory (DFT) results. In parallel, an education plan will be pursued involving the creation of the Solid State Chemistry Web Resource Library as part of the National Science Digital Library, as well as the development of materials for this library.
NON-TECHNICAL SUMMARY: Intermetallic phases form a broad family of compounds of immense importance to materials science. They adopt a diverse array of crystal structures that has yet to be accounted for with chemical bonding concepts. The absence of a theoretical framework for understanding and predicting the preferred crystal structures of these phases is a limiting factor in the design of new metallic materials with useful properties for hydrogen storage, catalysis, and superconductivity. In this SSMC/DMR-supported project, a joint theoretical and experiment approach is taken to develop understanding the driving forces underlying the crystal structures of these phases, and to gain some degree of control over these structures. The approach draws a common theme that has been perceived in some of the most complex intermetallic crystal structures: structural complexity can be linked to a tension between mutually exclusive bonding types coexisting in the same phase. In this project, new compounds will be sought out by inducing such tension through the selection of combinations of elements with inherent conflicts in the preferred types of chemical bonding and atomic packing. This approach to the design of new intermetallic structures has the potential of facilitating the development of new alloys for a wide range of applications. Several of the compounds to be investigated are also anticipated to have useful materials properties for hydrogen storage and superconductivity. The educational and social impacts of this work will also be considerable: the project will include the creation of the Solid State Chemistry Web Resource Library, a repository of educational materials for chemistry teachers and instructors interested in including current topics in materials science in their classes. The project will promote diversity in science through the participation of members of underrepresented groups.
