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Instruments / Technical Area	Publication Details	Published	Actions
I22-Small angle scattering & Diffraction	Understanding the emergence of the boson peak in molecular glasses Mario Gonzalez-Jimenez , Trent Barnard , Ben A. Russell , Nikita V. Tukachev , Uroš Javornik , Laure-Anne Hayes , Andrew J. Farrell , Sarah Guinane , Hans M. Senn , Andrew J. Smith , Martin Wilding , Gregor Mali , Motohiro Nakano , Yuji Miyazaki , Paul Mcmillan , Gabriele C. Sosso , Klaas Wynne Nature Communications 14 DOI: 10.1038/s41467-023-35878-6 Diamond Proposal Number(s): [28529] Open Access Show Abstract ▼ Abstract: A common feature of glasses is the “boson peak”, observed as an excess in the heat capacity over the crystal or as an additional peak in the terahertz vibrational spectrum. The microscopic origins of this peak are not well understood; the emergence of locally ordered structures has been put forward as a possible candidate. Here, we show that depolarised Raman scattering in liquids consisting of highly symmetric molecules can be used to isolate the boson peak, allowing its detailed observation from the liquid into the glass. The boson peak in the vibrational spectrum matches the excess heat capacity. As the boson peak intensifies on cooling, wide-angle x-ray scattering shows the simultaneous appearance of a pre-peak due to molecular clusters consisting of circa 20 molecules. Atomistic molecular dynamics simulations indicate that these are caused by over-coordinated molecules. These findings represent an essential step toward our understanding of the physics of vitrification.	Jan 2023
B22-Multimode InfraRed imaging And Microspectroscopy	Polyamorphism mirrors polymorphism in the liquid–liquid transition of a molecular liquid Finlay Walton , John Bolling , Andrew Farrell , Jamie Macewen , Christopher D. Syme , Mario González-Jiménez , Hans Martin Senn , Claire Wilson , Gianfelice Cinque , Klaas Wynne Journal Of The American Chemical Society DOI: 10.1021/jacs.0c01712 Diamond Proposal Number(s): [20351] Open Access Show Abstract ▼ Abstract: Liquid-liquid transitions between two amorphous phases in a single-component liquid have courted controversy. All known examples of liquid–liquid transitions in molecular liquids have been observed in the supercooled state suggesting an intimate connection with vitrification and locally favored structures inhibiting crystallization. However, there is precious little information about the local molecular packing in supercooled liquids meaning that the order parameter of the transition is still unknown. Here, we investigate the liquid–liquid transition in triphenyl phosphite and show that it is caused by the competition between liquid structures that mirror two crystal polymorphs. The liquid–liquid transition is found to be between a geometrically frustrated liquid to a dynamically frustrated glass. These results indicate a general link between polymorphism and polyamorphism and will lead to a much greater understanding of the physical basis of liquid–liquid transitions and allow the systematic discovery of other examples.	Apr 2020

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