A team of researchers from the University of Chicago and UC San Diego has uncovered a class of materials that appear to defy conventional physics. Under certain conditions, these materials don’t behave as expected—instead of expanding when heated or compressing under pressure, they do the opposite.
The study, recently published in Nature, focuses on oxygen-redox (OR) materials, which have gained attention for their energy storage potential. These materials are of particular interest in battery development, as they can store higher amounts of energy than conventional compounds. However, they have long been hindered by stability issues caused by structural disorder.
In their stable state, these OR materials conform to the laws of thermodynamics. But when pushed into a metastable state—a delicate, temporary balance—they begin to behave in ways that challenge long-standing physical models. For instance, the researchers observed negative thermal expansion: the material contracts when heated. Specifically, the contraction rate was recorded at −14.4(2) × 10⁻⁶ °C⁻¹, directly contradicting the Grüneisen relationship, a principle that normally explains why materials expand with heat.
Things get even stranger under pressure. Instead of compressing, the material expands when subjected to uniform external force—a phenomenon known as negative compressibility. According to study co-author Prof. Minghao Zhang, this effect mirrors the inverse thermal response. “If you compress a particle of the material in every direction, it will expand,” he explained.
The research also revealed that these unusual behaviors are not permanent. By applying specific electrical voltages, scientists were able to return the material to its original state—restoring both its structure and performance. This finding could have significant implications for electric vehicle battery life. “When we apply the voltage, we drive the material back to its pristine state,” Zhang noted. “Your battery will be like new.”
The potential applications extend well beyond energy storage. Materials with near-zero or negative thermal expansion could prove valuable in precision engineering, where dimensional stability is critical—such as in aerospace, electronics, and even building construction. “In architecture, you don’t want key components to constantly shift in volume due to temperature changes,” Zhang said.
While the findings are still at an early stage, they offer a new way of thinking about how materials can be designed to interact with energy. Instead of merely storing or conducting electricity, these materials can be reshaped by it—reversing wear, managing stress, and potentially extending the lifespan of devices.
The next phase of research will focus on fine-tuning redox chemistry to control these effects more reliably and scale the findings for industrial applications. As co-author Bao Qiu put it, “One of the goals is bringing these materials from research to real-world use.”
