Meijer Bernet E, Dixey Richard J C, Demmel Franz, Perry Robin, Walker Helen C, Phillips Anthony E
School of Physical and Chemical Sciences, Queen Mary University of London, London E1 4NS, UK.
ISIS Neutron and Muon Source, Rutherford Appleton Laboratory, Didcot OX11 0QX, UK.
Phys Chem Chem Phys. 2023 Mar 29;25(13):9282-9293. doi: 10.1039/d2cp05412d.
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 kg. 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.
高熵有序-无序相变可用于高效且环保的压电热固态冷却。本文报道了原型塑性晶体金刚烷中的压电热效应。金刚烷具有106 J K⁻¹ kg⁻¹的巨大等温可逆熵变。极低的滞后现象意味着在小于200巴的压力差下即可实现这一熵变。构型熵仅占总熵变的约40%；其余部分归因于振动效应。通过中子光谱和超胞晶格动力学计算发现，这种振动熵变主要是由与分子旋转对应的声学模式在高熵相中的软化引起的。我们将这种动力学差异归因于低熵相中的“互锁”状态与高熵相中的球状行为之间的对比。尽管金刚烷是一种具有近似球形分子的简单范德华固体，但这种方法可用于设计更复杂的压电热分子晶体。此外，本研究表明超胞晶格动力学计算能够准确描绘取向无序对声子谱的影响，为研究更复杂材料中的振动熵、热导率及其他热力学效应铺平了道路。
