Dynamics in the ordered and disordered phases of barocaloric adamantane
Dynamics in the ordered and disordered phases of barocaloric adamantane
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高压金刚烷有序相和无序相的动力学
DOI：
10.1039/d2cp05412d
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发表时间：
2023
影响因子：
3.3
通讯作者：
Meijer B
中科院分区：
文献类型：
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作者：
Meijer B
高熵有序-无序相变可用于高效且环保的压热固态冷却。这里的压热效应是在一个典型的塑料晶体，金刚烷报告。金刚烷具有巨大的等温可逆熵变，为106 J K−1 kg−1。极低的滞后意味着这可以在压力差小于200 bar的情况下实现。振动熵只能占总熵变的40%左右，其余的是由于振动效应。利用中子能谱和超晶胞晶格动力学计算，发现这种振动熵变主要是由对应于分子旋转的声学模式的高熵相的软化引起的。我们将这种动力学上的差异归因于低熵阶段中的“互锁”状态与高熵阶段中的类球体行为之间的对比。虽然金刚烷是一种简单的具有近球形分子的货车范德华固体，但这种方法可以用于设计更复杂的压热分子晶体。此外，这项研究表明，超晶胞晶格动力学计算可以准确地映射取向无序对声子谱的影响，为研究更复杂材料中的振动熵，热导率和其他热力学效应铺平了道路。
High-entropy order–disorder phase transitions can be used for efficient and eco-friendly barocaloric solid-state cooling. Here the barocaloric effect is reported in an archetypal plastic crystal, adamantane. Adamantane has a colossal isothermally reversible entropy change of 106 J K−1 kg−1. Extremely low hysteresis means that this can be accessed at pressure differences less than 200 bar. Configurational entropy can only account for about 40% of the total entropy change; the remainder is due to vibrational effects. Using neutron spectroscopy and supercell lattice dynamics calculations, it is found that this vibrational entropy change is mainly caused by softening in the high-entropy phase of acoustic modes that correspond to molecular rotations. We attribute this difference in the dynamics to the contrast between an ‘interlocked’ state in the low-entropy phase and sphere-like behaviour in the high-entropy phase. Although adamantane is a simple van der Waals solid with near-spherical molecules, this approach can be leveraged for the design of more complex barocaloric molecular crystals. Moreover, this study shows that supercell lattice dynamics calculations can accurately map the effect of orientational disorder on the phonon spectrum, paving the way for studying the vibrational entropy, thermal conductivity, and other thermodynamic effects in more complex materials.