Using 4D synchrotron X-ray microtomography rigs for time-resolved X-ray diffraction experiments: applications with the Mjölnir suite

Damien Freitas, Dominik Daisenberger, Simon Hunt, Ian Butler, Danielle Duggins, James Gilgannon, Christina Reinhard, Zhixin Liang, Neil Bourne

Synchrotron 4D X-ray microtomography provides unique insights into evolving microstructures during deformation, fluid flow and mineral transformations, but offers limited access to crystallographic information such as phase composition, lattice strain, and stress. Conversely, synchrotron X-ray diffraction (XRD) provides direct crystallographic measurements but is commonly restricted to small sample volumes and specialised sample environments. Here, we demonstrate the use of the Mjölnir and Heitt Mjölnir miniature triaxial deformation rigs, originally developed for 4D synchrotron microtomography, as platforms for time-resolved high-energy XRD experiments. Using experiments performed at beamline I15 (Diamond Light Source) supported by theoretical analysis, we evaluate diffraction contributions from pressure vessels and ancillary components, establish practical beamline setup and acquisition procedures, and assess controls on diffraction quality. We show that high-quality diffraction data can be acquired through X-ray-transparent pressure vessels, enabling phase identification, reaction tracking and lattice-strain measurements in representative sample volumes of geological materials. The rotational symmetry of the rigs further enables rocking, sweeping and mapping acquisition strategies, improving powder statistics while preserving realistic sample geometries and boundary conditions. These results provide a practical framework for integrating XRD with synchrotron microtomography and open new opportunities for linking crystallographic evolution to four-dimensional microstructural evolution during in situ experiments.