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Anomalous Liquids: Common features of Water, Metallic glassformers, and Chalcogenide PCMs (Phase Change Materials)
  Molecular Physics seminar

Friday 19 August 2016
from 14:00 to 15:00
at FA31
Speaker : Austen Angell (School of Molecular Sciences, Arizona State University)
Abstract : Liquid water has long held the mantle of "Most anomalous liquid" because of its bizarre behavior in the liquid state, particularly under supercooling. Despite contrary opinions, its diverging response functions and relaxation times are widely believed to be due to close approach to a second critical point, this time between two liquids of different density. Direct confirmation by laboratory studies has been precluded by diverging ice crystallization rates that develop as the critical domain is approached. Recently however, not only have other tetrahedral liquids been shown to have similar behavior (at least some silica models)(1) but related phenomena (fragile-to-strong liquid transitions) have been promoted as explanations of the rapid crystallization onset in supercooling metallic glassformers (2). Most recently, observations such as the phenomenological similarities in the warmup behavior of hyperquenched glassy water and hyperquenched glassy PCM* chalcogenides, (3) have led to the suggestion that a fast liquid-liquid phase change might be acting as an "Ostwald stage" to the crystallization process that is fundamental to the action of the PCMs* (4). In this seminar, we will review the experimental findings that lie behind the above commentary, discuss some recent successful strategies for revealing the seminal liquid-liquid event in the case of aqueous systems, and then look into the possibility of applying similar strategies to the elucidation of what might be going on in the other systems. *PCM: Phase Change Materials are under study for fast rewritable digital memory systems. (1) Lascaris, E., Hemmati, M., Buldyrev, S. V., Stanley, H. E. & Angell, C. A. Search for a liquid-liquid critical point in models of silica. J. Chem. Phys. 140,, 224502:doi: 224510.221063/224501.4879057 (2014). (2) Zhang, C., Hu, L., Yue, Y. & Mauro, J. C. Fragile-to-strong transition in metallic glass-forming liquids. J.Chem. Phys. 133, 014508 (2010). (3) Kalb, J. A., Wuttig, M. & Spaepen, F.. J. Mater. Res. 22, 748-754 (2007). (4) Wei, S., Luca, P. & Angell, C. A. Phase change alloy viscosities down to Tg by Adam Gibbs equation fittings to excess entropy data: a fragile-to-strong transition. J. Appl. Phys. 118, 034903 (2015).

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