Pressure dependence of rotational dynamics in barocaloric ammonium sulfate
Pressure dependence of rotational dynamics in barocaloric ammonium sulfate
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DOI：
10.1103/physrevb.106.064302
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发表时间：
2022-01
影响因子：
3.7
通讯作者：
Bernet E. Meijer;Guanqun Cai;F. Demmel;H. Walker;A. E. Phillips
中科院分区：
文献类型：
--
作者：
Bernet E. Meijer;Guanqun Cai;F. Demmel;H. Walker;A. E. Phillips
使用压热材料的固态冷却是一种环保、廉价和高效的冷却方式。为了设计出可供使用的压热化合物，必须了解它们在工作条件下的热力学行为。为此，我们研究了分子离子晶体硫酸铵在压力下的旋转动力学，提供详细的洞察其大的压热效应的起源。使用准弹性中子散射实验，我们表明，铵阳离子的旋转是由压力促进在低熵相，随着旋转的“跳跃”运动的频率增加的压力诱导相变的接近。我们解释这种不寻常的行为在竞争的氢键网络的两个阶段所代表的。这项工作包括最近开发的用于中子散射的低背景高压气体电池的第一批结果，展示了其在压力下获得高精度分子动力学测量的能力。
Solid-state cooling using barocaloric materials is a promising avenue for eco-friendly, inexpensive and highly efficient cooling. To design barocaloric compounds ready for deployment, it is essential to understand their thermodynamic behaviour 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 behaviour 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.