X-ray and neutron scattering

Abstract:

In this work we expand the family of ZIFs capable of being melt-quenched into a vitreous phase with the first Mn-based glass. This is achieved by preparing two new Mn-based ZIFs with topologies dia-c and znivia solvent-free synthesis and subsequent melting. This study also provides a direct comparison of metal effects on melting and decomposition behaviour, highlighting the relationship between bond strength and thermal properties.

Abstract:

Carbon has a central role in biology and organic chemistry, and its solid allotropes provide the basis of much of our modern technology1. However, the liquid form of carbon remains nearly uncharted2, and the structure of liquid carbon and most of its physical properties are essentially unknown3. But liquid carbon is relevant for modelling planetary interiors4, 5 and the atmospheres of white dwarfs6, as an intermediate state for the synthesis of advanced carbon materials7, 8, inertial confinement fusion implosions9, hypervelocity impact events on carbon materials10 and our general understanding of structured fluids at extreme conditions11. Here we present a precise structure measurement of liquid carbon at pressures of around 1 million atmospheres obtained by in situ X-ray diffraction at an X-ray free-electron laser. Our results show a complex fluid with transient bonding and approximately four nearest neighbours on average, in agreement with quantum molecular dynamics simulations. The obtained data substantiate the understanding of the liquid state of one of the most abundant elements in the universe and can test models of the melting line. The demonstrated experimental abilities open the path to performing similar studies of the structure of liquids composed of light elements at extreme conditions.

Abstract:

We report the solvent-free synthesis of a crystalline heterometallic imidazolate derivative with formula [Fe₁Zn₂(im)₆(Him)₂], designated MUV-25, incorporating both iron and zinc. The structure imposes strict positional constraints on the metal centres due to the lattice containing distinct geometric coordination sites, tetrahedral and octahedral. As a consequence, each metal is exclusively directed to its specific coordination site, ensuring precise spatial organization within the lattice. Atom locations were meticulously monitored utilizing X-ray diffraction (single crystal and total scattering) and XAS techniques, demonstrating that the tetrahedral sites are occupied exclusively by zinc, and the octahedral sites are occupied by iron. This combination of metal centres results, upon heating, in a structural phase transformation to the zni topology at a very low temperature. Further heating causes the melting of the solid, yielding a heterometallic MOF-derived glass. The methodology lays the groundwork for tailoring crystalline structures to advance the development of novel materials capable of melting and forming glasses upon cooling.

Abstract:

We present 50-fs, single-shot measurements of the x-ray thermal diffuse scattering (TDS) from copper foils that have been shocked via nanosecond laser ablation up to pressures above ∼135 GPa. We hence deduce the x-ray Debye–Waller factor, providing a temperature measurement. The targets were laser-shocked with the DiPOLE 100-X laser at the High Energy Density endstation of the European X-ray Free-Electron Laser. Single x-ray pulses, with a photon energy of 18 keV, were scattered from the samples and recorded on Varex detectors. Despite the targets being highly textured (as evinced by large variations in the elastic scattering) and with such texture changing upon compression, the absolute intensity of the azimuthally averaged inelastic TDS between the Bragg peaks is largely insensitive to these changes, and allowing for both Compton scattering and the low-level scattering from a sacrificial ablator layer provides a reliable measurement of T /Θ2 D, where ΘD is the Debye temperature. We compare our results with the predictions of the SESAME 3336 and LEOS 290 equations of state for copper and find good agreement within experimental errors. We, thus, demonstrate that single-shot temperature measurements of dynamically compressed materials can be made via thermal diffuse scattering of XFEL radiation.