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

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.

Our work directly addresses one of the most pressing concerns currently facing UK society, as recognised in the Government's Industrial Strategy: the need for clean cooling. Although our work on materials discovery is clearly only the first step of a long path towards commercial exploitation, the UK's existing strength in the field of cryogenics will be a substantial advantage in developing the materials identified in this project towards market as rapidly as possible. Furthermore, in the current uncertain economic climate, commercial research and development is necessarily conservative. Academic work, such as this, that contributes to understanding what makes a good material will reduce the need for trial-and-error searching, making subsequent targeted work more feasible.

Cryogenics is an important part of many other fields of science, and, for instance, both the Rutherford Appleton Laboratory and National Physical Laboratory have in-house cryogenics teams. Engaging with these engineers will offer a further possible route to exploitation, in bespoke apparatus for particular experiments; this will be faster than large-scale commercial application and may provide a good opportunity for proof-of-concept in future work originating from this project.

As well as its potential industrial impact, our work addresses the relationship of disorder to material functionality, a major and important research question in modern materials chemistry and physics. Our work will be of academic interest in the UK and internationally, as outlined above, across the broad fields of chemistry, physics, crystallography, and materials science. Our engagement with the Institute of Physics, Royal Society of Chemistry, Thomas Young Centre, and ISIS user community will help to generate a network of potential academic beneficiaries of this work.

All data and analysis associated with this work will be archived at ISIS and/or QMUL; we hope that this will provide a valuable reference for future academic and industrial work in this field.

Both of the applicants have substantial public engagement experience and are committed to continuing to engage the public in our work; in this we are supported by dedicated in-house teams at both QMUL and ISIS. Crystal engineering is visually appealing while environmental issues are sadly topical; we believe our work has the potential to capture the imagination of both school students and the public at large.

We note finally that this research project will be of direct benefit to the PDRA, who will receive training in cutting-edge experimental and computational research techniques and be well placed to continue a career in UK academia or industry.