M A T E R I A L S F O R T O M O R R O W ' S I N N O V A T I V E A N D S U S T A I N A B L E I N D U S T R Y

S C I E N T I F I C H I G H L I G H T S

5 8 H I G H L I G H T S 2 0 2 3 I

X-ray scattering techniques probe the multilevel organisation of magnetite mesocrystals

Advanced X-ray scattering techniques have been used to investigate mesocrystals nanostructured materials with multi-length-scale structure. A combination of methods applied to the assemblies of particles of varying size and shape enhances understanding of mesocrystal growth mode and choice of structural motif.

Mesocrystals a form of nanostructured material, usually defined as a nanocrystal superstructure with a common crystallographic orientation exhibit a multiple-length-scale structure, which is a prerequisite of many interesting phenomena. Mesocrystals can occur naturally in abiotic and biogenic minerals, or can be synthesised artificially [1]. Resolving the mesocrystal structure is quite challenging due to their structuration on different length scales. The combination of small- and wide-angle X-ray scattering (SAXS and WAXS) techniques offers the possibility of non-destructively probing mesocrystalline structures simultaneously, over multiple length scales to reveal their microscopic structure. A fundamental understanding of the multiscale organisation of mesocrystals is potentially beneficial for applications in various fields such as catalysis, surface- enhanced Raman scattering, electrodes, lithium-ion batteries and biomedicine. Magnetite nanoparticles have attracted significant attention in the past years due to their tendency to self-assemble into superstructures that exhibit superparamagnetic properties, even on the mesoscopic scale. Understanding both the external and internal structure of magnetite mesocrystals is therefore crucial to specify the complex structure magnetism relationship of the material.

Fig. 41: SEM images illustrating the morphology of magnetite

mesocrystals (1st column) related to WAXS (2nd column) and SAXS

(3rd column) high symmetry planes. Red arrows denote

reciprocal lattice translations of magnetite, black arrows denote reciprocal lattice translations of

the mesocrystalline packing. 4th column: Packing of nanoparticles

for corresponding trigonal, monoclinic, and tetragonal

structures. One family of facets is labelled by three orthogonal

directions of magnetite.