Unipd research. Fluctuating effects in x-ray exposed atoms as glass become fluid

24.01.2023

Glass is made by rapidly cooling a liquid - think of a common glass object formed by cooling a molten liquid. During this process, the glassy state atoms fluctuate, similar to liquids. However, their configuration remains almost fixed, meaning the atoms are constrained to their equilibrium position and move within the material only over extremely long times. Researchers found that when exposing glass to a beam of X-rays of sufficient intensity, it is possible to induce movement of the atoms inside the glass: subjected to X-rays, glass flows, like liquids.

The origin of this phenomenon remains debatable. Researchers aim to uncover this phenomenon with the publication of Stochastic atomic acceleration during the X-ray-induced fluidization of a silica glass in PNAS. The work of Francesco Dallari, Alessandro Martinelli, Federico Caporaletti, Michael Sprung, Giacomo Baldi, and Giulio Monaco is a collaboration between the Department of Physics and Astronomy of the University of Padua, the Physics Institute of the University of Amsterdam, the German DESY Research Centre of Hamburg, and the Physics Department of the University of Trento. The publication sheds new light on how atoms, exposed to X-rays, move within the disordered structure of glass over otherwise unattainable distances over a short amount of time.

This observable dynamic follows a law defined as HyperTransport, a motion where the distance travelled by the atoms accelerates over time. This motion not only occurs in a simple diffusion (think of a drop of coffee extending into a cup of milk) but even more when a particle moves at a constant speed in a certain direction.

After sufficient irradiation, these defects become dense (quite numerous). Atoms then move in response to the small charges that randomly "illuminate" the material. Normally, atoms move with a series of sudden accelerations, somewhat like balls in a pinball machine with a trajectory characterized by many short displacements interspersed with surprisingly long displacements following a probability known as the Lévy stable law of distribution.

This research shows a possible new strategy for modifying, and thus ultimately controlling, the physical properties of glass.