Atomic origins of the barocaloric effect
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PhD Thesis
Embargoed until: 2024-04-29
Reason: Author request
Embargoed until: 2024-04-29
Reason: Author request
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Conventional vapour-compression cooling techniques are inefficient and environmentally damaging. They cause ozone depletion, comprise about 25% of global electricity consumption, and yield 10% of greenhouse emissions. Solid-state cooling using barocaloric materials offers a promising alternative: these materials cannot escape into the atmosphere, are non-toxic and cheap, and offer greater cooling efficiency. The barocaloric effect is a change in entropy in response to pressure, and the largest of those effects are found in the family of molecular crystals. However, much is still unknown about the effect of atomic structure on the barocaloric properties; such insights would enable intelligent barocaloric design, allowing their features to be optimised and creating a pathway towards a sustainable revolution in cooling. This thesis looks to further the understanding of the barocaloric effect in molecular crystals on the atomic scale. The studies utilise neutron scattering and lattice dynamics calculations, often under pressure, providing unique insight into the geometry and dynamics under working conditions. Chapters 3 and 4 reveal that ammonium sulfate’s strong barocaloric reponse originates from competing hydrogen bond networks, opening up a novel avenue for barocaloric exploration. Chapter 5 focuses on adamantane, an archetypal ‘plastic’ crystal with characteristically weak intermolecular interactions. Adamantane has easily excited rotational modes, which are responsible for its extremely low driving pressure and low operating temperature, making it an ideal candidate for replacing toxic ultra-low temperature refrigerants such as ammonia. Finally, chapter 6 reveals that cation mobility in the ionic plastic crystal quinuclidinium hexafluorophosphate causes not only a strong barocaloric reponse, but also lies at the heart of its ion-conducting properties. This multifunctional behaviour could be harnessed to boost its cooling capacity, while the fact that ion mobility unusually decreases with temperature raises new questions in the still poorly understood mechanisms of ion mobility in plastic crystals.
Authors
Meijer, BCollections
- Theses [4125]