Atomic structure and dynamics of barocaloric frameworks for solid-state cooling

从使摩天大楼适合居住到冷却核磁共振扫描中使用的高功率磁铁，各种温度下的制冷技术是现代社会的核心。然而，最常用的基于蒸汽压缩的制冷循环在环境上是不可持续的，它所依赖的气体会导致臭氧消耗和全球变暖。因此，全球迫切需要新的冷却技术。这类技术中最有前途的一种是基于一种被称为压热学的材料。当对这些材料施加压力时，组成原子排列的有序程度就会发生变化，从而提高或降低材料的温度。通过在高压和低压状态之间来回循环，可以形成一个冷却循环，将热量从冷藏区域抽出。然而，只有少数这样的材料是已知的。阻碍这项技术广泛应用的主要瓶颈是简单地确定和优化合适的高压材料。在这个项目中，我们将研究一系列新发现的属于金属有机框架的高压热电化合物。这些材料很有希望成为气压热学材料，原因如下：它们对压力的微小变化非常敏感；它们经常经历如上所述的有序-无序相变；从理论上讲，通过调整这些材料的成分来调整它们的特性是可能的，例如增加气压效应。然而，有太多可能的组件通过试错来测试它们。相反，我们需要的是系统地了解究竟是什么原子水平的特征产生了我们的目标材料的显著的压热特性。我们的研究计划旨在达到这种理解。我们将在我们的目标材料上进行中子（以及x射线和拉曼）散射实验：这些实验不仅适合绘制原子的位置，而且适合绘制原子的运动。为了补充我们的实验数据，我们还将对这些材料进行计算机模拟。我们的实验数据将证实我们的模型很好地符合现实，而我们的模拟数据将提供仅从实验中无法提取的信息。结合我们的实验和模拟数据，我们将阐明从这些材料的结构和动力学中产生气压效应的方式。基于这些结果，我们将预测在金属有机框架中实现更大的气压效应的方法。我们的研究结果将有助于指导未来的探索，为帮助尽快开发技术上可利用的材料提供路线图。

Refrigeration technologies across a wide range of temperatures are at the core of modern society, from making skyscrapers inhabitable to cooling the high-power magnets used in MRI scans. Yet the refrigeration cycle most commonly used, based on vapour compression, is environmentally unsustainable, relying on gases that contribute both to ozone depletion and global warming. As a result, there is an immediate and widely-recognised global need for new cooling technologies.One of the most promising such technologies is based on materials known as barocalorics. As pressure is applied to these materials, the degree of order with which the component atoms are arranged changes, which raises or lowers the temperature of the material. By cycling back and forth between high- and low-pressure states, a cooling cycle can be created that pumps heat out of a refrigerated area. However, only a few such materials are known. A major bottleneck delaying this technology from widespread use is simply identifying and optimising suitable barocaloric materials.In this project, we will investigate a series of newly-discovered barocalorics that belong to the broad family of metal-organic frameworks. These materials are promising barocalorics for several reasons: they are highly susceptible to small changes in pressure; they often undergo order-disorder phase transitions of the sort described above; and in theory it is possible to adjust the components of these materials in order to tune their properties, for instance to increase the barocaloric effect. However, there are far too many possible components to test them all by trial and error. Instead, what is needed is a systematic understanding of exactly what atomic-level features produce our target materials' remarkable barocaloric properties.Our research programme aims to achieve exactly this understanding. We will perform neutron (alongside X-ray and Raman) scattering experiments on our target materials: these are ideally suited to map not just the positions but also the motion of the atoms. To complement our experimental data, we will also perform computer simulations of these materials. Our experimental data will confirm that our models match reality well, while our simulated data will provide information that could not be extracted from experiment alone.Combining our experimental with our simulated data, we will elucidate the way in which the barocaloric effect emerges from these materials' structure and dynamics. Based on these results, we will predict ways to achieve an even greater barocaloric effect in metal-organic frameworks. Our results will help to direct future exploration, providing a road map to help develop technologically exploitable materials as quickly as possible.