An X-ray Diffractometer for Extreme Conditions Research

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We are interested in the effect of pressure on molecular solids. In organic materials pressure modifies and rearranges intermolecular contacts such as hydrogen bonds and van der Waals contacts leading to rich polymorphic diversity. Pressure is thus a very effective tool for exploring the structural flexibility, the so-called 'energy landscapes', of organic solids, a very important factor in the development of pharmaceuticals, which also provides valuable data for computational work such as first-principals prediction of crystal structures. Changes in primary molecular bond distances tend not to be observed in organic systems at least up to 10 GPa (100 000 atm). By contrast, work on metal coordination compounds has revealed that, unlike organic systems, intramolecular metal-ligand bonding can be affected by pressure. This makes pressure a perfect tool for exploring the relationship between structure and properties in functional coordination materials such as molecular magnets: a material can be studied in different states of distortion, providing the most direct way to study correlations between structure and properties. The same methodology can be used to study metals, minerals and other extended materials, to show, for example, how rocks change their structures in planetary interiors, how materials can be modified for advanced technological applications and how materials change structure under the influence of shock waves during detonations, and how transport can be made more efficient by controlling the response of additives to the extreme conditions of modern engines. Pressure can be applied to a sample using a diamond anvil cell, in which a sample is held between the faces of two diamonds. When load is applied to the diamonds, pressure many thousands of times atmospheric pressure can be generated at the sample. The sample can then be studied using single-crystal X-ray diffraction, which is the most precise and convenient way to obtain structural information on the atomic scale, to reveal how the material responds to pressure.In this project we seek funding for a diffractometer that will enable these studies to be carried out at The Centre for Science at Extreme Conditions, an institute dedicated to extreme conditions research at The University of Edinburgh. The new instrument will be equipped with state-of-the-art detector and X-ray sources, to enable data to be collected very quickly but with high precision. We will design and build new pressure cells which will enable data to be obtained simultaneously at high pressure and variable temperature. The new facility will enable much more complex supramolecular materials to be studied than has hitherto been possible. The combination of these facilities will provide a unique instrument which enables variation of two fundamentally important thermodynamic variables of temperature and pressure to provide deep insight into the factors which govern phase stability in solid materials.