晶格振动和离子扩散介导的塑性晶体中的巨大可逆压热效应
Colossal reversible barocaloric effects in a plastic crystal mediated by lattice vibrations and ion diffusion
摘要：
固态冷却和加热方法有望成为目前温室气体压缩循环和低效燃料燃烧加热器的更可持续的替代方案。静水压力（$p$）驱动的压热效应（BCE）在大的绝热温度变化（$|ΔT| \sim 10$ K）和巨大的等温熵变（$|ΔS| \sim 100$ JK $^{-1}$ kg $^{-1}$）方面特别令人鼓舞。然而，由于不可逆性问题，BCE通常需要大的压力变化，并且相当大的$|ΔT|$和$|ΔS|$很少在相同的材料中实现。在这里，我们证明了存在的巨大的和可逆的BCE在LiCB $_{11}$ H $_{12}$，一个众所周知的固体电解质，在其附近的有序-无序相变在$\approx 380$ K。具体来说，对于$Δp \approx 0.23$ $(0.10)$ GPa，我们测量了$|ΔS_{\rm rev}| = 280$ $(200)$ JK $^{-1}$ kg $^{-1}$和$|ΔT_{\rm rev}| = 32$ $(10)$ K，它们分别与在类似压力条件下获得的最先进的压热位移相媲美。此外，在宽的温度范围内，$0.1$ GPa量级的压力变化产生巨大的可逆压热强度$\approx 2$ JK $^{-1}$ kg $^{-1}$ MPa $^{-1}$。进行了分子动力学模拟，以量化的晶格振动，分子重新取向和离子扩散上公开的巨大的BCE的作用。有趣的是，晶格振动被发现对$|ΔS|$贡献最大，而锂离子的扩散，尽管只轻微地增加了伴随的熵变，但在实现分子有序-无序相变方面至关重要。我们的工作扩大了知识的塑料晶体，并应激励调查的BCE在各种固体电解质显示离子扩散和伴随的分子取向紊乱。
英文摘要：
Solid-state methods for cooling and heating promise a more sustainable alternative to current compression cycles of greenhouse gases and inefficient fuel-burning heaters. Barocaloric effects (BCE) driven by hydrostatic pressure ($p$) are especially encouraging in terms of large adiabatic temperature changes ($|ΔT| \sim 10$ K) and colossal isothermal entropy changes ($|ΔS| \sim 100$ JK$^{-1}$kg$^{-1}$). However, BCE typically require large pressure shifts due to irreversibility issues, and sizeable $|ΔT|$ and $|ΔS|$ seldom are realized in a same material. Here, we demonstrate the existence of colossal and reversible BCE in LiCB$_{11}$H$_{12}$, a well-known solid electrolyte, near its order-disorder phase transition at $\approx 380$ K. Specifically, for $Δp \approx 0.23$ $(0.10)$ GPa we measured $|ΔS_{\rm rev}| = 280$ $(200)$ JK$^{-1}$kg$^{-1}$ and $|ΔT_{\rm rev}| = 32$ $(10)$ K, which individually rival with state-of-the-art barocaloric shifts obtained under similar pressure conditions. Furthermore, over a wide temperature range, pressure shifts of the order of $0.1$ GPa yield huge reversible barocaloric strengths of $\approx 2$ JK$^{-1}$kg$^{-1}$MPa$^{-1}$. Molecular dynamics simulations were carried out to quantify the role of lattice vibrations, molecular reorientations and ion diffusion on the disclosed colossal BCE. Interestingly, lattice vibrations were found to contribute the most to $|ΔS|$ while the diffusion of lithium ions, despite adding up only slightly to the accompanying entropy change, was crucial in enabling the molecular order-disorder phase transition. Our work expands the knowledge on plastic crystals and should motivate the investigation of BCE in a variety of solid electrolytes displaying ion diffusion and concomitant molecular orientational disorder.
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