Understanding relaxation processes in glasses is essential for linking their microscopic dynamics to macroscopic mechanical behavior. As a liquid is cooled toward the glass-transition temperature (Tg), its relaxation dynamics separate into two distinct processes: the structural (α) relaxation, involving large-scale cooperative rearrangements, and the faster Johari-Goldstein (JG) or β relaxation, …
The Johari–Goldstein or beta relaxation has a clear spectroscopic signature in fragile glass-formers, including many organic and metallic systems, while is less or not at all visible in strong glass-formers, including most network-forming systems as oxides and chalcogenides. This is often related to the reduced structural heterogeneity characteristic of strong …
The yield point marks the beginning of plastic deformation for a solid subjected to sufficient stress, but it can alternatively be reached by x-ray irradiation. We characterize this latter route in terms of thermodynamics, structure and dynamics for a series of GeSe3 chalcogenide glasses with different amount of disorder. We …
Synchrotron-radiation-based techniques are a powerful tool for the investigation of materials. In particular, the availability of highly brilliant sources has opened the possibility to develop techniques sensitive to dynamics at the atomic scale such as X-ray photon correlation spectroscopy (XPCS). XPCS is particularly relevant in the study of glasses, which …
A solid loaded beyond the yield stress loses its elastic properties and becomes plastic. From a microscopic point of view, this limit corresponds to the condition where plastic regions become so densely packed that they give rise to system-spanning structures. This limit for glasses is abrupt, which makes experimental investigations …
Upon X-ray irradiation, a number of glasses undergo a fluidization process: The atoms move from their original positions while keeping a similar distribution of interatomic distances, as for two snapshots of a liquid. This process has been studied looking at the atomic displacements over interatomic distances. We here extend these …
Speckle-based experiments, in particular X-ray Photon Correlation Spectroscopy (XPCS), are among the ones that benefit most from the development of next generation light sources. The key quantity that determines whether or not it will be possible to perform an XPCS experiment is the speckle contrast β, which measures the visibility of …
Despite the technological importance of supercritical fluids, controversy remains about the details of their microscopic dynamics. In this work, we study four supercritical fluid systems─water, Si, Te, and Lennard-Jones fluid─via classical molecular dynamics simulations. A universal two-component behavior is observed in the intermolecular dynamics of these systems, and the changing …
We introduce a setup to measure high-resolution inelastic x-ray scattering at the High Energy Density scientific instrument at the European X-Ray Free-Electron Laser (XFEL). The setup uses the Si (533) reflection in a channel-cut monochromator and three spherical diced analyzer crystals in near-backscattering geometry to reach a high spectral resolution. …
When a liquid is cooled to produce a glass its dynamics, dominated by the structural relaxation, become very slow, and at the glass-transition temperature Tg its characteristic relaxation time is about 100 s. At slightly elevated temperatures (~1.2 Tg) however, a second process known as the Johari-Goldstein relaxation, βJG, decouples from the …
