Crystallography, a powerful lens for Materials Science

The humain evolution has been always favoured by the discovery of new materials. In the last decades, special materials with unique and amazing optoelectronic properties like, for example, perovskites, attracted a growing scientific interest and revealed themselves promising and appealing candidates for technological applications (e.g., solar cells, LEDs, lasers, photodetector devices,..). Among them, the hybrid organic-inorganic perovskites, consisting of alternating layers of organic cations and inorganic corner-sharing octahedra, offer a great potential, relying on the large tunability of their optoelectronic properties: e.g., by changing the type of organic cations and/or the number of layers in the inorganic slabs, strong differences in the emitted wavelength can be observed. To optimize and tune the optoelectronic properties of new crystalline materials Crystallography plays a fundamental guiding role: a successful structure determination process gives precious insights into the structure-property relationships of the investigated compounds. The ab-initio structure solution process of crystalline materials is not always straightforward, it can be hampered by their small size and/or their low crystallinity and weak diffraction power; for example, in the case of a few-?m-thick laminar single crystals, a crystallographic study based on conventional laboratory X-ray sources usually fails. The access to non-conventional high-brilliance X-ray sources (i.e., the use of synchrotron radiation) allows to reduce the size of the single crystals that can be successfully characterized and to increase the complexity of the crystal structures that can be determined by X-ray diffraction data. To enhance the power of Crystallography, making it an effective lens for studying also challenging cases, the use of synchrotron radiation is fundamental and can reveal itself an obliged choice, as proved by some recent cases of successful ab-initio structure solution of new hybrid organic-inorganic perovskites [1-4], via powder diffraction [1] and single crystal diffraction [2-4]. Very recently, the use of synchrotron radiation opened the door also to the structural investigation of metal chalcohalides nanocrystalline materials by powder diffraction: e.g., the ab-initio structure solution of bismuth chalcohalides [5] that belong to a still poorly explored world of new materials of interest for applied nanotechnology and that, similarly to perovskites, show appealing optoelectronic properties. The latest outcomes of the structural characterization by synchrotron X-ray diffraction data in the case of challenging compounds of interest for Materials Science (i.e., new hybrid organic-inorganic perovskites [1-4] and metal chalcohalides [5,6]) will be presented. References [1] A. Ray et al., Adv. Mater. 34 (2022) Article Number: 2106160. [2] L. Polimeno et al., Nat. Nanotechnol. 16 (2021) 1349-1354. [3] M. Cinquino et al., Adv. Mater. 33 (2021) Article Number: 2102326. [4] B. Dhanabalan et al., Adv. Mater. 33 (2021) 2008004. [5] D. Quarta et al., Angew. Chem. Int. Ed. (2022) Article Number: e202201747. [6] S. Toso et al., Nat. Commun. 13 (2022) Article Number: 3976.