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González-Jiménez M, Barnard T, Russell BA, Tukachev NV, Javornik U, Hayes LA, Farrell AJ, Guinane S, Senn HM, Smith AJ, Wilding M, Mali G, Nakano M, Miyazaki Y, McMillan P, Sosso GC, Wynne K. Understanding the emergence of the boson peak in molecular glasses. Nat Commun 2023; 14:215. [PMID: 36639380 PMCID: PMC9839737 DOI: 10.1038/s41467-023-35878-6] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2022] [Accepted: 01/05/2023] [Indexed: 01/15/2023] Open
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.
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Affiliation(s)
| | - Trent Barnard
- Department of Chemistry, University of Warwick, Warwick, UK
| | - Ben A Russell
- School of Chemistry, University of Glasgow, Glasgow, UK
| | | | - Uroš Javornik
- Slovenian NMR Centre, National Institute of Chemistry, Ljubljana, Slovenia
| | | | | | - Sarah Guinane
- School of Chemistry, University of Glasgow, Glasgow, UK
| | - Hans M Senn
- School of Chemistry, University of Glasgow, Glasgow, UK
| | - Andrew J Smith
- Diamond Light Source, Harwell Science and Innovation Campus, Harwell, UK
| | | | - Gregor Mali
- Department of Inorganic Chemistry and Technology, National Institute of Chemistry, Ljubljana, Slovenia
| | - Motohiro Nakano
- Research Center for Thermal and Entropic Science, Osaka University, Osaka, Japan
| | - Yuji Miyazaki
- Research Center for Thermal and Entropic Science, Osaka University, Osaka, Japan
| | - Paul McMillan
- Department of Chemistry, University College London, London, UK
| | | | - Klaas Wynne
- School of Chemistry, University of Glasgow, Glasgow, UK.
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