Understanding the emergence of the boson peak in molecular glasses

González-Jiménez, Mario, Barnard, Trent, Russell, Ben A., Tukachev, Nikita V., Javornik, Uroš, Hayes, Laure-Anne, Farrell, Andrew J., Guinane, Sarah, Senn, Hans M., Smith, Andrew J., Wilding, Martin, Mali, Gregor, Nakano, Motohiro, Miyazaki, Yuji, McMillan, Paul, Sosso, Gabriele C. and Wynne, Klaas 2023. Understanding the emergence of the boson peak in molecular glasses. Nature Communications 14 (1) , 215. 10.1038/s41467-023-35878-6

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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.

Item Type:	Article
Date Type:	Published Online
Status:	Published
Schools:	Chemistry
Additional Information:	License information from Publisher: LICENSE 1: URL: http://creativecommons.org/licenses/by/4.0/, Type: open-access. There is a correction to this article at https://doi.org/10.1038/s41467-023-36662-2 https://orca.cardiff.ac.uk/158155 Author correction to article added 16/02/23 - https://doi.org/10.1038/s41467-023-36662-2
Publisher:	Nature Research
Date of First Compliant Deposit:	16 January 2023
Date of Acceptance:	5 January 2023
Last Modified:	11 Oct 2023 20:58
URI:	https://orca.cardiff.ac.uk/id/eprint/155903

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