The project focused on two main scientific topics: i) the knowledge of the relaxation dynamics in supercooled liquids over different length scales from several interparticle distances down to the atomic scale, and ii) the connection between atomic motion and structure in glasses and its evolution under in-situ and ex-situ high pressure hydrostatic compression.
For the first topic, we probed the dynamics and structure in two different ultra-viscous metallic liquids on approaching the glass transition from the supercooled liquid phase. This work, discussed in Comm. Phys. 5, 316, (2022), helps elucidating the microscopic mechanisms beyond the glass transition, a dynamical process that keeps fascinating scientists since many decades. When a liquid glass-former is cooled close to the glass transition temperature, its viscosity increases rapidly over several order of magnitude in a very narrow temperature range until the system falls out of equilibrium and becomes a disordered solid, a glass, with no apparent structural changes. This process corresponds to an increasingly sluggish particle motion whose nature is still highly debated, mainly due to the lack of approriate experimental methods able to probe the particle motion. In our work, we provide such information from the wavelength dependence of the structural relaxation process and show that the dynamics not only reflects the topological order of the material, but also the chemical short-range order, which can lead to a surprising slowdown of the structural relaxation process at the mesoscopic scale. We also found a strong connection between the degree of heterogeneous dynamics of the supercooled liquid – a fascinating feature of all glass formers – and the rigidity of the melt structure, supporting the idea of a structural origin beyond the glass transition.
Additional progress has been made also in the study of the effect of in-situ high pressure compression in the atomic motion in metallic glasses by performing the first experiments that coupled in-situ high pressure technologies with X-ray Photon Correlation Spectroscopy. As discussed in PNAS, 120, e2302281120, (2023) and Acta Mat. 255,119065 (2023), we found a non-trivial evolution of the atomic motion under high pressure compressions which exhibits different intriguing features that could explain a surprising rejuvenation and strain hardening reported recently under ex-situ densifications.
