Materials Research Lecture
Fragility is a concept that is often correlated with glass formability. It is generally defined in terms of dynamical aspects of the liquid, usually based on the rate of increase of the viscosity as a function of the inverse temperature scaled to the glass transition temperature, Tg (i.e. Tg/T). Our experimental studies of the temperature dependence of the liquid structure factor, S(q), for a range of metallic alloy liquids demonstrate a link between structural and kinetic fragility [1]. A new scaling temperature, TA, is also identified, which, based on the results of molecular dynamics simulations, corresponds to the onset of cooperative flow in the liquid [2]. Our recent experimental and MD results show that the rate of short-range and medium-range structural ordering in the liquid accelerates below the temperature of this dynamical crossover, further demonstrating the link between structure and dynamics. Further, for all metallic glass-forming liquids studied Tg @ TA/2, suggesting a deep connection between the onset of cooperative dynamics and the glass transition [3], which is supported by our recent MD results [4]. Finally, by scaling the inverse temperature by TA, and the magnitude of the viscosity by the extrapolated viscosity at infinite temperature, ho, a universal curve from TA down to Tg is obtained for all of the metallic liquids studied. On average, ho is equal to the product of the number density and Planck's constant [5]. These points will be discussed and suggestions made for further studies.
Research was partially supported by the National Science Foundation (DMR-12-06707) and NASA (NNX10AU19G).
[1] N. A. Mauro, M. E. Blodgett, M. L. Johnson, A. J. Vogt and K. F. Kelton, Nature Comm., 5, 4616 (2014).
[2] T. Iwashita, D. M. Nicholson and T. Egami, Phys. Rev. Lett. 110, 205504 (2013).
[3] M. Blodgett, T. Egami, Z. Nussinov and K. F. Kelton, Sci. Reports, 13836 ( 2015), doi:10.1038/srep13837.
[4] R. Soklaski, V. Tran, Z. Nussinov, K. F. Kelton, L. Yang, Phys. Rev. B (submitted; arXiv:1502.01739).
[5] Z. Nussinov, F. S. Nogueira, M. Blodgett and K. F. Kelton (arXiv:1409.1915).
More about the speaker:
Kenneth Kelton received his Ph.D. in Applied Physics from Harvard University in 1983, where he remained as a postdoctoral fellow until 1985. He joined the Physics faculty at Washington University in 1985 as an Assistant Professor, was promoted to Associate Professor in 1990, and to Professor in 1994. Professor Kelton has been a visiting fellow at several Colleges within Cambridge University, most recently as an Overseas Visiting Scholar in St. John's College in 2003. In 2005, he was elected as a Fellow of the American Physical Society. In October 2006, Kelton was installed as the inaugural Arthur Holly Compton Professor in Arts & Sciences at Washington University. He was inducted into the Hall of Distinction at Arkansas Tech University in 2008, and received the ISMANAM Senior Scientist Award (International Symposium on Amorphous, Nanocrystalline and Metastable Materials) in 2010. He served as the Chair of the Physics Department at Washington University from 2007 – 2012 and is the inaugural director of the Institute of Materials Science and Engineering at Washington University. During a recent sabbatical at the Joint Institute of Neutron Science (Oak Ridge National Laboratory) he finished construction and testing of the first facility for elastic and inelastic neutron scattering studies of supercooled metallic liquids with a spallation source. He has published over 270 scientific articles, one book, "Nucleation in Condensed Matter," and is on the editorial advisory board for the Journal of Non-Crystalline Solids and Philosophical Magazine Letters. Kelton's current research interests include nucleation processes in condensed phase, in particular precipitation and crystallization of metallic and silicate glasses, metallic glass formation, structural, dynamical and thermophysical properties of supercooled liquids and the origin of liquid fragility and it's relation to glass formation.