When 10:15 AM - 11:30 AM Mar 24, 2023
Where 1013 H.H. Dow
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"Frustrated and Allowed Structural Transitions: Lessons in Materials Design from Complex Intermetallic Phases"


Daniel C. Fredrickson
University of Wisconsin

Abstract:  Intermetallic phases—solid state compounds that form upon alloying metallic elements together—comprise a realm of immense structural diversity:  their structures range from simple variants of the familiar fccbcc and hcp lattices, to the giant cubic unit cells of NaCd2 (>1,000 atoms/cell) and Al55.4Cu5.4Ta3.9 (23,134 atoms/cell), to quasicrystals such as YbCd5.7 whose geometries defy description with 3-dimensional unit cells.  A limiting factor in realizing the broad technological applications promised by this diversity of atomic arrangements is our inability to understand, let alone control, the crystal structures of these compounds.  An emerging theme in the study of these phases is a link between structural complexity and driving forces that are familiar from molecular chemistry.  One focus of our group’s research has been pursuing this theme using an interaction of theory and experiment.  In this seminar, we will discuss some of our recent advances in this pursuit, including (1) the development of the theoretical tools for creating graphical and intuitive representations the electronic and atomic size requirements of crystal structures, and (2) the Frustrated and Allowed Structural Transitions principle for understanding and predicting how structural phenomena arise from the coordination or competition between the electronic and atomic size factors. 

 

Bio:  Daniel Fredrickson is a Professor of Chemistry at the University of Wisconsin-Madison whose research group combines the theory and experiment in the development of predictive principles for the structural chemistry and physical behavior of intermetallic phases.  Central themes of this research are (1) creating of theoretical tools that translate the dense numerical output of DFT calculations into guidance for the discovery of new structural phenomena, and (2) tracing the origins of complex structures, such as incommensurately modulated arrangements, to bonding issues in simpler parent phases.  His interests in the relationships among bonding, molecular orbital theory, and structure have roots in his Ph.D. research with Profs. Roald Hoffmann and Stephen Lee at Cornell University, while his endeavors in solid state synthesis and crystallography grow from with his post-doctoral work with Prof. Sven Lidin, then at Stockholm University.