Diamond Light Source - Annual Review 2022/23 - Concise Edition

D I A M O N D L I G H T S O U R C E A N N U A L R E V I E W 2 0 2 2 / 2 3 D I A M O N D L I G H T S O U R C E A N N U A L R E V I E W 2 0 2 2 / 2 3 28 29 1 2 Crystallography Group T he Crystallography Group comprises the High-Resolution Powder Diffraction beamline (I11), the Extreme Conditions beamline (I15), the X-ray Pair Distribution Function (XPDF) beamline (I15-1), and the Small-Molecule Single-Crystal Diffraction beamline (I19). Having these beamlines together in one science group allows us to fully exploit the technical and scientific expertise within its teams to provide the basis for future development and pioneering experiments. The Group’s beamlines use various techniques to study structural properties of crystalline, amorphous, and liquidmaterials indifferent conditions. These powerful facilities are used in awide range of science disciplines, including Condensed Matter Physics, Chemistry, Engineering, Earth and Materials, and Life Sciences. Studies in the past year have included structural changes in MOF under pressure, understanding the movements of electrons in complex molecules and Lithium-ion batteries. Porous framework materials compress like a spring under highmechanical pressure. Metal-organic frameworks (MOFs) are modular porous materials possessing a wide range of functions. Some MOFs reversibly switch between two different states, an open pore state with voids accessible for guest molecules and a closed pore state, where the voids of the framework are inaccessible for guest molecules. Usually, this transition is discontinuous, and only two different states/structures are accessible. Researchers wanted to generate a MOF system featuring a continuum of available states/structures between the open and the closed states. They used Diamond’s I15 beamline to investigate the high-pressure structural behaviour of a series of MOFs of the ZIF-62 family, which feature the same framework structure but possess various fractions of small- and large-sized organic linker molecules. At I15, they could use a dedicated hydraulic high-pressure cell for the experiments. The required pressure for pore closure increases with increasing fraction of the large-sized linker included in ZIF-62. For very large fractions of the larger linker, ZIF-62 continuously transforms from the open pore to the closed pore form with increasing pressure. Structure refinement and detailed analyses revealed that the pore size of the continuously transforming ZIF-62 derivative also gets continuously narrower and narrower with increasing pressure. The pressure driven open-pore to closed-pore transition of ZIF-62 could lead to applications of these materials as shock absorbers or nano-dampers. The material can be fine-tuned for a specific molecular separation task by applying a pressure that sets an appropriate pore size cut-off. Song J. et al. DOI: 10.1002/anie.202117565 Electronmovement between components of mechanically interlockedmolecules Controlling photoinduced charge transfer within molecules is a significant challenge. An international team of researchers previously demonstrated that a macrocycle (wheel-shaped molecule) could reversibly lose an electron. They wanted to see if threading an electron-accepting molecule through this macrocycle could make a mechanically interlocked system, known as a rotaxane, where the electron could be stimulated to hop from the wheel to the thread. They obtained the single crystal structure of the most complex compound, a hetero[4]rotaxane, using data from Diamond’s I19 beamline. A [4]rotaxane is a molecular thread passing through three wheel-shaped molecules. Crystal structures of such intricate molecular systems are incredibly rare, so it was valuable for this work to obtain this structure that showed the position and arrangement of all the interlocked pieces. In this study, combining the data from the synchrotron X-ray source with electron diffraction studies allowed the complete determination of the structure of this fascinating molecule. The movement of the electron can be stimulated with photons (laser light), which causes an electron to rapidly hop from the wheel to the thread. This event occurs at different rates in the different systems, which led the research team to conclude that a distinct wheel molecule was supplying the electron in each system. Understanding how to control the movement of electrons in complex molecular systems is useful in the construction of organic electronic devices, such as OLEDs and solar cells. Pearce, N. et al. DOI: 10.1038/s41467-022-28022-3 Local cation ordering in ‘disordered’ Li-ion cathodes The modern world relies on high-performance lithium-ion (Li-ion) batteries for numerous applications. Demand for these batteries is increasing, but current cathode materials limit the energy density and dominate the cost. In recent years, there has been a surge of interest in lithium rich cathodes with a cation Disordered Rock Salt (DRS) structure. DRS cathodes are relatively low cost, and their high first charge capacities offer tantalising promise for high- energy-density Li-ion batteries. However, they suffer from a large irreversible capacity loss on the first charge-discharge cycle. The origin of the capacity loss in DRS is not well understood. Researchers used operando techniques to investigate the evolution of the average structure, short-range ordering and charge during the cycling of a DRS, using both spectroscopic and structural probes. To understand the structural evolution of nanostructured DRS cathodes operando , they acquired pair distribution function (PDF) data at Diamond’s I15-1 beamline. This work provides insight into the design of better DRS cathodes and highlights the importance of local structures in the cyclability of battery materials. Furthermore, successful control of the coexistence of layered and DRS sublattices offers a novel route to electrode design, opening a new path to developing high-performance cathode materials. This research is an example of how multimodal, operando experiments across complementary techniques including HERFD-XANES, XES (Kβ main line, V2C), and X-ray Total Scattering (Bragg, XPDF), can aid the complete understanding of complex electrochemical processes in new battery materials. Diaz-Lopez, M. et al. DOI: 10.1039/D2TA04262B