Periodic Reporting for period 2 - CoherentGlasses (A coherent view of Glasses: How coherent x-rays can elucidate the complex dynamics of glasses)
Período documentado: 2022-09-01 hasta 2024-02-29
Glasses are essential materials in our daily life due to their ubiquitous occurrence in Nature, biomedical applications, communications and industrial products. Glasses include many kind of materials, from soft systems as plastics, pharmaceutical compounds and clays, to hard materials as windows, screens and optical sensors. These materials have common microscopic relaxation processes which control their macroscopic properties. Predict the evolution of these properties is a formidable challenge for academic research and is fundamental to ensure reliability in service, safe applications and optimized performances. This goal requires the development of precise relationships between structure, dynamics and macroscopic properties, a challenging task in glasses due to their out-of-equilibrium nature and the spontaneous temporal evolution of any of their properties during applications. Measuring and understanding atomic-scale mechanisms responsible for the macroscopic properties of glasses is therefore fundamental for both technological applications as well as from the theoretical point of view, to help building up a microscopic theory for glasses which is still missing.
Among all glasses, metallic glasses have attracted interest in the last decades due to their outstanding mechanical, elastic and thermal properties which place them among the most studied metallic materials. Notwithstanding the atomic mechanisms responsible for the evolution of many of their macroscopic properties are still far from being understood. This is even more the case in the presence of mechanical deformations, although its relevance for technological applications. The CoherentGlasses project goes at the heart of this issue by proposing a novel experimental approach to provide information on the atomic motion and structure in metallic glasses in an unprecedented explored spatial range and under extreme conditions of high temperature and pressure, providing thus unique information on the effect of deformations at the atomic level. For this purpose, the project takes advantage of the coherent properties of the x-rays delivered in 4th generation synchrotron sources, such as the ESRS-EBS European synchrotron, to perform studies of the atomic motion in disordered systems at extreme conditions. Coupling these results with state-of-the-art calorimetric techniques and structural studies, it will be possible to understand the physical mechanisms behind several intriguing features of glasses.
Among all glasses, metallic glasses have attracted interest in the last decades due to their outstanding mechanical, elastic and thermal properties which place them among the most studied metallic materials. Notwithstanding the atomic mechanisms responsible for the evolution of many of their macroscopic properties are still far from being understood. This is even more the case in the presence of mechanical deformations, although its relevance for technological applications. The CoherentGlasses project goes at the heart of this issue by proposing a novel experimental approach to provide information on the atomic motion and structure in metallic glasses in an unprecedented explored spatial range and under extreme conditions of high temperature and pressure, providing thus unique information on the effect of deformations at the atomic level. For this purpose, the project takes advantage of the coherent properties of the x-rays delivered in 4th generation synchrotron sources, such as the ESRS-EBS European synchrotron, to perform studies of the atomic motion in disordered systems at extreme conditions. Coupling these results with state-of-the-art calorimetric techniques and structural studies, it will be possible to understand the physical mechanisms behind several intriguing features of glasses.
The first part of 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 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.
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.
In the first part of the project we have made substantial progress beyond the state of the art. We have dedicated a large effort to couple the brightest coherent x-rays available in synchrotrons with cutting edge high pressure technologies to perform high energy X-ray Photon Correlation Spectroscopy (XPCS) experiments at extreme conditions of in-situ high pressure and temperature. These are very challenging experiments that require preservation of the x-rays coherence properties, extremely high stability in terms of sample position, pressure and temperature.
Thanks to these developments, we have been already able to provide unique information on the microscopic structural and dynamical mechanisms occurring under in-situ high pressure compression and decompression of metallic glasses at ambient temperature, from the onset of the perturbation up to a severely-deformed state. Future studies, will be dedicated to investigate the interplay between temperature and pressure on the microscopic relaxation dynamics of metallic glasses across the glass transition.
Thanks to these developments, we have been already able to provide unique information on the microscopic structural and dynamical mechanisms occurring under in-situ high pressure compression and decompression of metallic glasses at ambient temperature, from the onset of the perturbation up to a severely-deformed state. Future studies, will be dedicated to investigate the interplay between temperature and pressure on the microscopic relaxation dynamics of metallic glasses across the glass transition.