🔬 materials science

Break-down of the relationship between α-relaxation and equilibration in hydrostatically compressed metallic glasses

The study demonstrates that hydrostatic compression of metallic glasses creates unique metastable states that cannot be erased by simple $\alpha$ -relaxation upon heating, revealing that pressure-induced structural changes require an additional process beyond standard relaxation to reach equilibrium.

Original authors: Antoine Cornet, Jie Shen, Alberto Ronca, Shubin Li, Nico Neuber, Maximilian Frey, Eloi Pineda, Thierry Deschamps, Christine Martinet, Sylvie Le Floch, Daniele Cangialosi, Yuriy Chushkin, Federico Zont

Published 2026-02-10

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CC BY 4.0

Original authors: Antoine Cornet, Jie Shen, Alberto Ronca, Shubin Li, Nico Neuber, Maximilian Frey, Eloi Pineda, Thierry Deschamps, Christine Martinet, Sylvie Le Floch, Daniele Cangialosi, Yuriy Chushkin, Federico Zontone, Marco Cammarata, Gavin B. M. Vaughan, Marco di Michiel, Gaston Garbarino, Ralf Busch, Isabella Gallino, Celine Goujon, Murielle Legendre, Geeth Manthilake, Beatrice Ruta

Original paper licensed under CC BY 4.0 (http://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

The Mystery of the "Stubborn" Glass: Why Pressure Changes Everything

Imagine you have a large container of colorful LEGO bricks. Usually, if you shake the container (add heat), the bricks jumble around, settle into a predictable pattern, and eventually become a smooth, uniform soup of plastic. In the world of science, this "soup" is called a supercooled liquid, and the process of the bricks settling is called $\alpha$ -relaxation.

For decades, scientists believed that no matter how you messed up the arrangement of those bricks—whether you squeezed them, shook them, or froze them mid-jumble—once you heated them up into that "liquid soup" state, the bricks would "forget" their past and return to their original, standard arrangement.

This paper proves that, for certain metallic glasses, the bricks have a very long memory.

The Experiment: The High-Pressure Squeeze

The researchers took a specific type of "metallic glass" (a metal that is frozen in a messy, disordered state rather than a neat crystal lattice) and put it under immense pressure—like being at the bottom of a deep ocean, but much more intense.

They tested two main ways of squeezing:

The "Quick Freeze" (HPQG): Squeezing the liquid and then cooling it down fast. This made a very dense, stable glass.
The "Slow Squeeze" (HPAG): Squeezing the solid glass itself while it was still solid.

The Surprise: The "Rejuvenated" Glass

You might think that squeezing something makes it more "relaxed" and stable. But when they squeezed the solid glass (the HPAG), something weird happened. Instead of becoming a tighter, more organized structure, the atoms actually pushed apart in certain ways.

Analogy: Imagine squeezing a sponge. You expect it to get smaller and tighter. But imagine if, by squeezing it, you actually caused the internal fibers of the sponge to snap and rearrange into a springier, more "energetic" shape. The sponge hasn't just changed size; it has changed its personality.

The Big Discovery: The Memory That Won't Fade

Here is the "breakdown" mentioned in the title. Usually, heating a glass above its transition temperature is like hitting a "Reset Button." It’s supposed to erase the history of how the material was made.

However, the researchers found that when they heated these "squeezed" glasses, the Reset Button didn't work.

Even when the metal turned into a liquid, it didn't turn into the normal liquid. It turned into a new kind of liquid—one that flowed faster and had a different atomic structure. The "memory" of the high pressure stayed trapped in the atoms.

Why does this matter? (The "Broken Relationship")

The paper points out a "breakdown" in a fundamental rule of physics.

In most materials, there is a direct link between $\alpha$ -relaxation (the atoms moving around) and equilibration (the material returning to its natural state). It’s like saying, "Once the dancers start moving freely on the floor, the party is officially back to normal."

But in these compressed metallic glasses, the dancers (atoms) started moving, but the party never went back to normal. The music changed, the floor layout changed, and the dancers were following a completely different rhythm.

The takeaway: There is a "hidden" process happening. The $\alpha$ -relaxation (the movement) isn't enough to fix the structural damage or changes caused by the pressure. There is a much slower, deeper structural reorganization required to truly "reset" the material.

Why should we care?

This isn't just academic curiosity. If we can use pressure to "engineer" glasses that have specific, permanent properties—like being harder, more flexible, or more stable—we can create new high-tech materials for aerospace, electronics, or medical implants that are "tailor-made" by their history.

In short: Scientists have discovered that by squeezing glass, they can write a "permanent note" into its atomic structure that even heat cannot erase.

Technical Summary: Break-down of the relationship between $\alpha$ -relaxation and equilibration in hydrostatically compressed metallic glasses

1. The Problem

In the study of amorphous materials, a fundamental paradigm holds that the "memory" of any thermo-mechanical treatment (which places a glass in a metastable state) can be erased by heating the material into the supercooled liquid phase. It is generally assumed that this erasure—the return to the equilibrium liquid state—is controlled by the primary structural relaxation process, known as $\alpha$ -relaxation.

While this assumption holds for thermally treated glasses, its validity under extreme mechanical constraints is unknown. Specifically, it is unclear whether high-pressure annealing (HPA) creates a state that can be "reset" to the pristine liquid state simply by heating it back to ambient pressure above the glass transition temperature ( $T_g$ ).

2. Methodology

The researchers investigated a series of $\text{Pt}_{42.5}\text{Cu}_{27}\text{Ni}_{19.5}\text{P}_{21}$ metallic glasses using a multi-modal experimental approach:

Sample Preparation: They distinguished between two compression protocols at 5 and 10 GPa:
- High-Pressure Quenched Glasses (HPQGs): Compressed and cooled from the supercooled liquid phase ( $T_{comp} > T_g(P)$ ).
- High-Pressure Annealed Glasses (HPAGs): Compressed while in the glassy state ( $T_{comp} < T_g(P)$ ).
Thermodynamics: Flash Differential Scanning Calorimetry (FDSC) was used to measure enthalpy recovery, $T_g$ , and fictive temperature ( $T_f$ ) using ultra-fast heating rates (up to 1000 K/s) to prevent premature relaxation during measurement.
Structure: Synchrotron X-ray Diffraction (XRD) and Pair Distribution Function (PDF) analysis were employed to probe the static structure factor $S(q)$ , medium-range order (MRO), and atomic cluster connectivity (e.g., icosahedral vs. P-centered clusters).
Dynamics: X-ray Photon Correlation Spectroscopy (XPCS) was used to measure the Intermediate Scattering Function (ISF) and structural relaxation times ( $\tau_\alpha$ ) in the supercooled liquid phase to determine if the system reached equilibrium.

3. Key Results

Counterintuitive Stability (HPAGs): Unlike HPQGs, which become more stable and relaxed, HPAGs exhibit structural rejuvenation. Despite being compressed, they show a higher fictive temperature ( $T_f$ ) and lower thermal stability compared to the reference glass.
Anomalous Structural Expansion: Upon heating, HPAGs undergo a surprising structural expansion of the first coordination shells (up to $\sim 9$ Å) before densifying. This is accompanied by a decrease in structural order (increased FWHM of the first sharp diffraction peak) during the transition, contrasting with hyper-quenched glasses which order upon heating.
Cluster Reorganization: The structural changes are linked to a redistribution of atomic motifs. While as-cast glasses favor 2- and 3-atom connection modes (associated with icosahedral and P-centered clusters), HPAGs show a decrease in these modes and an increase in 4-atom connection modes (suggesting the formation of octahedrons) during the pressure-release/heating process.
Breakdown of $\alpha$ -relaxation/Equilibration Link: Most significantly, when HPAGs are heated above $T_g$ at ambient pressure, they do not revert to the pristine supercooled liquid. Instead, they transform into a new, distinct liquid state characterized by faster dynamics (lower $\tau_\alpha$ ) and different structural signatures. XPCS confirmed that these new dynamics are stationary, meaning the system is in a stable, non-equilibrium state relative to the original liquid.

4. Key Contributions

Discovery of Irreversibility: The study proves that high-pressure annealing can induce a permanent change in the material's potential energy landscape that cannot be erased by simple thermal cycling.
Identification of a New Mechanism: The authors propose that the $\alpha$ -relaxation is not the sole process governing equilibration in these systems. An additional, slower mechanism must exist to facilitate the full structural recovery to the equilibrium liquid.
Polyamorphic Implications: The results suggest the possibility of a length-scale-dependent devitrification process or a pressure-induced glass-glass transition that creates new metastable liquid states.

5. Significance

This work challenges a cornerstone of glass physics: the idea that the supercooled liquid is a unique equilibrium state that erases all prior history. By demonstrating that pressure can be used to "engineer" new, stable, non-equilibrium liquid and glassy states with tailored properties, the research opens new avenues for materials design via extreme conditions. It also highlights the necessity of using microscopic probes (like XPCS and XRD) to define thermodynamic equilibrium, as macroscopic measurements may fail to capture the complexity of disordered systems under pressure.