In a major advancement, researchers have demonstrated negative thermal expansion with a large coefficient of −14.4(2) × 10-6 °C-1 in oxygen-redox (OR) active materials, offering new possibilities for designing zero-thermal-expansion materials.
Study: Negative thermal expansion and oxygen-redox electrochemistry. Image Credit: Tum ZzzzZ/Shutterstock.com
A recent article published in Nature details how this unusual behavior arises from thermally driven disorder–order transitions in OR-active materials. This discovery provides a practical framework for developing functional materials that could greatly benefit industries like construction.
Understanding the Science Behind the Breakthrough
To appreciate the significance of this breakthrough, it helps to first understand how structural disorder affects materials. Structural disorder in materials often leads to unique phenomena, stemming from the complex interactions between thermodynamic and electrochemical properties. OR electrochemistry, in particular, has shown the potential to push material capacity limits by introducing structural disorder, though sometimes at the expense of electrochemical reversibility.
Typically, the thermal expansion of solids is explained through the Grüneisen relationship, which links expansion to the anharmonic behavior of the crystal lattice. However, OR materials appear to behave differently, suggesting that dynamic disorder–order transitions play a major role.
Methods
Building on this idea, a team from the University of Chicago’s Pritzker School of Molecular Engineering (UChicago PME), together with visiting scientists from the University of California, San Diego, set out to explore the thermal and electrochemical behaviors of metastable OR-active materials.
Their approach involved putting these materials through their paces, subjecting them to heat, pressure, and electric fields, and then comparing their responses to those of more conventional materials. They also carefully examined how applying an electrochemical driving force could alter the materials' internal structures.
What They Found — and Why It Matters
The results were striking: the OR-active material exhibited a strong negative thermal expansion, with a coefficient of −14.4(2) × 10-6 °C-1, directly linked to a disorder–order transition triggered by heat.
Even more impressive, the researchers discovered that they could largely restore structural disorder by tweaking the electrochemical driving force—specifically, by adjusting the cut-off voltages. Voltage changes during discharge hinted at almost complete recovery of the material’s original structure.
This ability to fine-tune the OR behavior gave researchers a powerful tool to precisely control the material’s thermal expansion properties. It also led them to propose a practical design strategy for crafting materials with zero thermal expansion, while offering new ways to tackle persistent challenges like voltage decay in electrochemical systems.
Adding another layer of fascination, the OR materials seemed to challenge traditional thermodynamics. In their stable state, they behaved normally. But in a metastable state, they flipped the script—shrinking when heated instead of expanding. Such unique tunability through redox chemistry opens up exciting possibilities, especially for applications in construction and advanced engineering.
Why It’s a Big Deal for Construction and Beyond
The successful demonstration of negative thermal expansion in metastable OR-active materials marks a major step forward. With this level of control, engineers could engineer how materials respond to heat, pressure, and electricity, which could transform the way we approach material design.
Zero-thermal-expansion materials are especially valuable in construction, where even small changes in material volume can cause cracks, warping, or mechanical failure over time. The materials studied here also exhibited negative compressibility under gigapascal-level pressure, meaning they could actually expand when compressed, a rare and highly desirable property for designing earthquake-resistant structures.
In short, by creating materials that shrink with heat and expand under pressure, researchers may be rewriting the basic rules of how we think about material behavior, with powerful implications for engineering, architecture, and energy technologies.
Journal Reference
Qiu, B. et al. (2025). Negative thermal expansion and oxygen-redox electrochemistry. Nature. DOI: 10.1038/s41586-025-08765-x, https://www.nature.com/articles/s41586-025-08765-x
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