Scientists unveil universal aging mechanism in glassy materials

Chinese Academy of Sciences Headquarters

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"Glass" has a unique and distinct meaning in physics—one that refers not just to the transparent material we associate with window glass. Instead, it refers to any system that looks solid but is not in true equilibrium and continues to change extremely slowly over time. Examples include window glass, plastics, metallic glasses, spin glasses (i.e., magnetic systems), and even some biological and computational systems.

When a liquid is cooled very quickly—a process called quenching—it doesn't have time to organize into a crystal but becomes stuck in a disordered state far from equilibrium. Its properties—like stiffness and structure—slowly evolve through a process called "aging."

Now, a research team from the Institute of Theoretical Physics of the Chinese Academy of Sciences has proposed a new theoretical framework for understanding the universal aging behavior of glassy materials.

The study reveals a fundamental mechanism that governs how glasses—from simple spin systems to complex network glasses such as amorphous silica—slowly evolve over time.

To understand the aging process, the researchers developed a generalized trap model (GTM) grounded in the material's energy landscape: a multidimensional map of all possible configurations and the energy barriers that separate them. According to the GTM, aging is driven by activated hopping across these energy barriers. A universal distribution of barrier heights, incorporating crucial finite-size corrections, governs the system's slow, nonequilibrium dynamics.

The theory predicts that during nonequilibrium aging, the system undergoes "weak ergodicity breaking" at a temperature higher than the conventional glass transition temperature. In statistical physics, "ergodic" refers to a system that explores all possible configurations consistent with its energy. In contrast, the term "ergodicity breaking" refers to an equilibrium system becoming trapped in a subset of possible states, unable to explore all configurations. Weak ergodicity breaking occurs in nonequilibrium systems and describes a system that continues to evolve but remains correlated with its initial configuration even after prolonged aging.

By applying the GTM to four distinct models, including the random energy model (a spin glass), the Weeks-Chandler-Andersen model (a simple atomic glass), and amorphous silica (a network glass), the researchers demonstrated that glass aging behavior follows universal mathematical laws. A key finding is that the logarithmic decay of the two-time correlation function, a hallmark of aging, is directly linked to the finite size of "activation clusters," or groups of particles that rearrange together during the aging process.

In the Weeks-Chandler-Andersen model, this insight allowed the researchers to extract a static length scale from the nonequilibrium dynamics, extending its observable growth range from a mere factor of two to three to a full order of magnitude. This provides strong supporting evidence for the random first-order transition (RFOT) theory, a leading theory of the glass transition.

This work provides a unified phase diagram that describes both ergodic and weakly non-ergodic phases in spin and structural glasses, offering a powerful tool for understanding these ubiquitous yet complex materials. These findings have implications not only for materials science but also for other complex systems, such as protein dynamics and even the training of deep learning algorithms, where similar slow relaxation processes are observed.

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Journal

Science Advances

DOI

10.1126/sciadv.aec4416 

Method of Research

Experimental study

Subject of Research

Not applicable

Article Title

Universal activated aging and weak ergodicity breaking in spin and structural glasses

ANCIENT NEW AGE

Chimps’ love for crystals could help us understand our own ancestors’ fascination with these stones

Ancestors of modern humans collected crystals for which they had no apparent use. A new chimp study could help researchers understand the roots of this infatuation

Frontiers

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image: 

Chimp Toti attentively observes the quartz crystal during Experiment 1. 

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Credit: García-Ruiz et al., 2026

Crystals have repeatedly been found at archaeological sites alongside Homo remains. Evidence shows hominins have been collecting these stones for as long as 780,000 years. Yet, we know that our ancestors did not use them as weapons, tools, or even jewelry. So why did they collect them at all?

Now, in a new Frontiers in Psychology study, scientists in Spain investigated which characteristics of crystals may have made them so fascinating to our ancestors. They designed experiments with chimpanzees – one of the two great ape species most closely related to modern humans – to identify the physical properties of crystals that may have attracted early hominins.

“We show that enculturated chimpanzees can distinguish crystals from other stones,” said lead author Prof Juan Manuel García-Ruiz, an Ikerbasque Research Professor on crystallography at the Donostia International Physics Center in San Sebastián. “We were pleasantly surprised by how strong and seemingly natural the chimpanzees’ attraction to crystals was. This suggests that sensitivity to such objects may have deep evolutionary roots.”

The Monolith

Modern humans diverged from chimps between six and seven million years ago, so we share substantial genetic and behavioral similarities. To find out if fascination with crystals is one of them, the researchers provided two groups of enculturated chimpanzees (Manuela, Guillermo, Yvan, Yaki, and Toti in group one and Gombe, Lulú, Pascual, and Sandy in group two) from the Rainfer Foundation with access to crystals.

In the first experiment, a large crystal – the monolith – was placed on a platform, along with a normal rock of similar size. While initially both objects caught the chimps’ attention, soon the crystal was preferred and the rock disregarded. Once they had removed it from the platform, all chimps inspected the crystal, rotating and tilting it so they could view it from specific angles. Yvan then picked up the crystal and decisively carried it to the dormitories.

Interest was strongest early after exposure and declined very gradually over time, the team observed. The same pattern is found in humans as the novelty of an objects fades. When caretakers tried to retrieve the crystal from the chimps’ enclosure, they had to exchange it for favored snacks: bananas and yogurt.

A crystal-clear preference

A second experiment showed that the chimps could identify and select smaller quartz crystals – similar in size to those collected by hominids – from a pile of 20 rounded pebbles within seconds. When pyrite and calcite crystals, which have different shapes than quartz crystals, were added to the pile, chimps still were able to pick out crystal-type stones. “The chimpanzees began to study the crystals’ transparency with extreme curiosity, holding them up to eye level and looking through them,” García-Ruiz said. Chimps repeatedly examined the crystals for hours.

Sandy, for example, carried pebbles and crystals in her mouth to a wooden platform where she separated them. “She separated the three crystal types, which themselves differed in transparency, symmetry, and luster, from all the pebbles. This ability to recognize crystals despite their differences amazed us,” García-Ruiz said. Chimps also do not usually use their mouths to carry objects, so this behavior could mean they were hiding them a behavior consistent with treating the crystals as valuable, the team pointed out.

Crystals in our minds

The study did not examine if some chimps were more interested or laid more claim to crystals than others, although future studies should take chimp personalities into account, the team said. “There are Don Quixotes and Sanchos: idealists and pragmatists. Some may find the transparency of crystals fascinating, while others are interested in their smell and whether they’re edible,” García-Ruiz pointed out. The chimps tested here also are used to contact with humans and familiar with objects not found in the natural world. Therefore, the same experiments should be carried out with less enculturated species, ideally wild apes.

The combined observations from the experiments identified both transparency and shape as alluring properties. It might have been the same qualities attracting early humans to these rocks. The clouds, trees, mountains, animals, and rivers of the natural world surrounding our ancestors were defined by curvature and ramification, so few items had straight lines and flat surfaces. Crystals are the only natural polyhedral, meaning the only natural solids with many flat surfaces. When early humans tried to make sense of their environment, their cognitive processes might have been drawn to patterns that were unlike what they knew. 

“Our work helps explain our fascination with crystals and contributes to the understanding of the evolutionary roots of aesthetics and worldview,” concluded García-Ruiz. “We now know that we’ve had crystals in our minds for at least six million years.”

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Journal

Frontiers in Psychology

DOI

10.3389/fpsyg.2026.1633599 

Method of Research

Experimental study

Subject of Research

Animals

Article Title

On the origin of our fascination with crystals

Article Publication Date

4-Mar-2026

Yvan's interaction with small crystals. He brought the crystal very close to his eye and inspected it carefully, repeating the action several times. This episodic inspection lasted for more than 15 minutes.

Credit

García-Ruiz et al., 2026

'The Monolith' used in experiment 1 is an elongated quartz crystal weighing 3.3 kg and 35 cm in height. 

In experiment 1, the crystal was placed on a pedestal which had been installed months prior to the experiments, so it did not constitute a novelty for the chimpanzees.

Credit

Aden Kahr

In experiment 2, Sandy separated three crystals from a pile of pebbles; on the right is close-up view of the three separated crystals: quartz (right), pyrite (up), and calcite (bottom left).

Credit

García-Ruiz et al., 2026

Yvan analyzing transparency of crystals. [VIDEO]1 

Yvan analyzing transparency of crystals. [VIDEO] 2

 

Electric field tunes vibrations to ease heat transfer

Smart ceramics reveal a new way to control heat transfer, boosting thermal conductivity nearly threefold

DOE/Oak Ridge National Laboratory

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image: 

Yellow waves show propagating atomic vibrations observed at ORNL’s Spallation Neutron Source. In a smart, switchable ceramic, an electric field aligns charges so vibrations along white field lines travel farther with fewer disruptions — boosting heat flow nearly threefold. 

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Credit: Phoenix Pleasant/ORNL, U.S. Dept. of Energy

New research from the Department of Energy’s Oak Ridge National Laboratory, in collaboration with The Ohio State University and Amphenol Corporation, challenges conventional understanding about controlling heat flow in solid materials. 

The study, published in PRX Energy, shows that applying an electric field to a ceramic material changes how phonons (tiny vibrations that carry heat) behave. Phonons with atoms moving along the field direction (poling direction) last longer than those with atoms moving perpendicular to the field. As a result, the material conducts heat almost three times more efficiently along the field direction than in perpendicular directions. This promising approach could lead to new solid-state devices that control heat flow in everyday technologies.

“Being able to control both how fast and in what manner heat flows could lead to devices that manage thermal energy far more efficiently,” said Puspa Upreti, an ORNL postdoctoral research associate.

Controlling heat flow is important for high-performance systems such as modern electronic coolers with no moving parts, energy converters that change heat into power, chip-based circuits used in everyday technology, and cogeneration systems, which capture and repurpose industrial heat. Regulating heat in these systems creates the right conditions for peak efficiency and performance.

The link between efficiency and heat flow is shown by the Carnot cycle, an idealized model of a heat engine that sets the highest possible efficiency by precisely controlling the transfer of heat between hot and cold reservoirs. In this study, applying an electric field removes barriers to phonon transport. This lets the vibrations travel farther, much like reducing traffic on a busy road, and improves heat conduction along the electric field direction, which leads to better efficiency.

Experiments took place at the Spallation Neutron Source, a DOE Office of Science user facility operated by ORNL. The researchers used advanced inelastic neutron scattering techniques to capture both the static arrangement of atoms (structure) and their movements (dynamics). Neutrons help scientists see exactly where the atoms are in the material and how they move, a concept recognized in the Nobel Prize-winning work by Clifford Shull and Bertram Brockhouse.

The detailed dataset from the Spallation Neutron Source offers a clear understanding of how adjusting the electric field not only speeds up the phonons but also extends their lifetimes, which is key for developing future ways to manage heat.

The study focused on a special type of ceramic called relaxor-based ferroelectrics. When these ceramics are exposed to an electric field, tiny electrical charges inside them align. This alignment reduces scattering of the heat-carrying vibrations, allowing energy to flow more efficiently. The crystals used in this study were carefully grown and then subjected to the electric field, or “poled,” by Raffi Sahul at Amphenol Corporation. The work produced solids that enable precise control of energy flow.

ORNL senior researcher Michael Manley designed and led the inelastic neutron scattering experiments along with ORNL senior R&D staff member Raphaël Hermann. “Earlier work on bulk ferroelectric materials achieved modest improvements in thermal conductivity of 5 percent to 10 percent, while the new measurements reveal an enhancement close to 300 percent — mainly because the phonons are able to travel much longer before they stop,” Manley said.

By integrating their thermal conductivity measurements with neutron scattering data, the researchers directly connected changes in heat flow to the behavior of atomic vibrations within the crystal. The late Professor Joseph Heremans of Ohio State designed the thermal conductivity experiments and guided doctoral candidate Delaram Rashadfar through the data interpretation. “While earlier work led us to expect only a modest effect, observing a threefold difference turned out to be a significant result,” said Rashadfar. “Professor Heremans always stressed the importance of trusting the data first and letting the theory follow.”

This work was funded by the DOE Basic Energy Sciences program, and other contributing partners.

UT-Battelle manages ORNL for the DOE’s Office of Science. The Office of Science is the largest supporter of basic research in the physical sciences in the United States and is committed to addressing some of the most pressing challenges of our time. For more information, visit energy.gov/science. — Scott Gibson

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DOI

10.1103/5d1z-wg4p 

Method of Research

Experimental study

Subject of Research

Not applicable

Article Title

Electric Field Control of Phonon Lifetimes and Thermal Conductivity in Relaxor-Based Ferroelectric