Abstract
Solid-state cooling using barocaloric materials is a promising avenue for ecofriendly, inexpensive, and highly efficient cooling. To design barocaloric compounds ready for deployment, it is essential to understand their thermodynamic behavior under working conditions. To this end, we have studied the rotational dynamics in the molecular-ionic crystal ammonium sulfate under pressure, providing detailed insight into the origin of its large barocaloric effect. Using quasielastic neutron scattering experiments, we show that rotation of the ammonium cations is facilitated by pressure in the low-entropy phase, with the rotational “hopping” motion increasing in frequency as the pressure-induced phase transition is approached. We explain this unusual behavior in terms of the competing hydrogen-bond networks represented by the two phases. This work includes the first results of a recently developed low-background, high-pressure gas cell for neutron scattering, showcasing its power in obtaining high-precision measurements of molecular dynamics under pressure.
- Received 27 January 2022
- Accepted 21 June 2022
DOI:https://doi.org/10.1103/PhysRevB.106.064302
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.
Published by the American Physical Society