Pressure dependence of atomic dynamics in barocaloric ammonium sulfate: I. Rotations

Meijer, Bernet E.; Cai, Guanqun; Demmel, F.; Walker, Helen C.; Phillips, Anthony E.

doi:10.48550/arxiv.2201.11512

Cited by 1 publication

(2 citation statements)

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“…The structure of ammonium sulfate, with different hydrogen bond networks in the two phases, is rather unique, and it is perhaps difficult to see how these competing structures could have been rationally designed. However, as we noted in the first paper in this series [19] the entropic benefits of the flat energy landscape demonstrate that crystal engineering of structures with similar competing hydrogen-bond networks may provide a promising route to new caloric materials.…”

Section: Discussionmentioning

confidence: 86%

“…We have studied the dynamics of the molecular ions in ammonium sulfate in detail by neutron scattering as a function of pressure, under conditions equivalent to those that would be required in a device application, and present our results in two papers. In our first paper, we discussed quasielastic neutron scattering, focussing on the rotational motion of the individual ammonium ions [19]. In this second paper, we use inelastic neutron scattering (INS) combined with density-functional theory (DFT) simulation to study the collective vibrational motion of both ammonium and sulfate ions.…”

Section: Introductionmentioning

confidence: 99%

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Pressure dependence of atomic dynamics in barocaloric ammonium sulfate: II. Vibrations

Yuan¹,

Meijer²,

Cai³

et al. 2022

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Ammonium sulfate is a giant inverse barocaloric material that is cheaply and commercially available. Exploiting its potential for cooling applications requires an understanding of the mechanism driving the entropy change. Here we report an investigation by inelastic neutron scattering and density functional theory of the phonons under working conditions of temperature and pressure. We find excellent agreement between the experimental and calculated results. The ammonium librational modes that are crucial to the entropy change are identifiable by their negative Grüneisen parameter. Our results connect the differences in structure across the phase transition to those in the atomic dynamics, suggesting a route towards designing new caloric materials.

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Section: Discussionmentioning

confidence: 86%

Section: Introductionmentioning

confidence: 99%