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

点击翻译按钮获取中文摘要

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.