Physics Colloquium - Friday, April 6th, 2007, 4:00 P.M.

E300 Math/Science Center; Refreshments at 3:30 P.M. in Room E200

Ken Kelton
Arthur Holly Compton Professor Department of Physics and Center for Materials Innovation Washington University, St. Louis

Bringing down Barriers - Coupled Phase Transitions in Liquids and Glasses

Recently our synchrotron X-ray diffraction studies of electrostatically-levitated samples, demonstrated that the liquids of many transition metals and their alloys develop strong icosahedral order with supercooling. In a Ti-Zr-Ni liquid this ordering couples with the nucleation of the ordered phase. Regions of the ordered liquid act as a template for the nucleation of the icosahedral phase, blurring the traditional distinction between homogeneous and heterogeneous nucleation. This is one example of a coupled nucleation process; others include cases if coupling between magnetic or chemical ordering and nucleation. Such nucleation processes are not properly described by the commonly used classical theory of nucleation. Coupled nucleation processes and their consequences for the crystallization of liquids and glasses are discussed. The relation between the growth of icosahedral order and the glass transition is also pointed out. Supported by the NSF under grants DMR 03-07410 and DMR-0606065, NASA under contract NNM04AA016, and AFOSR under contract 9550-05-1-0110.