The pressure response of metallic glasses unveiled

Metallic glasses are disordered materials that interest scientists due to their combination of the strength of metals and the structural disorder of glass, which gives them elasticity, corrosion resistance and magnetic and electronic properties.

Researchers are currently exploring metallic glasses for a wide range of applications, from biomedical implants to microscale devices and industrial components. They also want to study them from a fundamental point of view, in order to find out how disorder affects the structure of materials. “Despite the importance of glasses, we still know little about the conditions under which they form and the dynamics of the atoms they comprise”, explains Beatrice Ruta, researcher at the CNRS’Institut Néel, visiting scientist at the ESRF and awardee of the ERC Starting Grant CoherentGlasses (Grant agreement ID: 948780).

Glasses and glass-like materials don’t stop moving completely when they “freeze” into a solid. Inside them, atoms and molecules are still shifting around in different ways, and this motion—called “relaxation”—controls how the glass ages and performs over time. The main type, called α-relaxation, is a slow, cooperative movement of many particles. It explains why liquids can flow and determines how fragile or strong a glass is when cooled. Another type, called β-relaxation, is fastr and more local—it’s like tiny “wiggles” of atoms that continue even below the glass transition temperature (when the glass stops flowing).

Pressure and temperature are the two key parameters both affect the relaxation modes. Whilst there are many temperature studies on glasses, pressure studies are scarce, owing to the experimental difficulties to perform in-situ high pressure experiments.

A team led by Ruta has now found the relaxation mechanisms in glasses under high pressure.

The scientists combined in-situ and ex-situ high-pressure experimental techniques with fast-scan calorimetry and synchrotron X-ray diffraction from the ESRF’s ID13 and ID15A beamlines.  “We wanted to test the belief that high pressure always makes materials denser and more stable and instead show that, in metallic glasses, compression depends on how atoms move and interact at the atomic level”, explains Jie Shen, postdoctoral researcher and co-corresponding author of the publication.

The results reveal two distinct relaxation mechanisms under high pressure: In the β-relaxation regime, compression drives the system with reduced atomic mobility and enhanced structural disorder, without appreciable density changes. On the other hand, α-relaxation under pressure promotes density-driven structural ordering that improves thermal stability.

The team noticed that the shift between these different behaviours always happens at the same relative temperature compared to the glass transition point, no matter how much pressure is applied.

“We can now separate the effects of structure and relaxation on glass stability and this opens the doors to design glasses with specific properties by carefully controlling heat and pressure”, concludes Ruta.

Reference:

Shen et al., Sci. Adv. 11, eadz7406 (2025) 3 October 2025

Text by Montserrat Capellas Espuny

Top image: Schematic of relaxation modes under high pressure and the resulting recovered glass states.