Low-Pressure Phase Transitions in a Layered Material

Researchers from Washington State University and the University of North Carolina at Charlotte have discovered a hybrid zinc telluride-based material, β-ZnTe(en)_0.5, that undergoes significant structural changes under relatively low pressure. This material could someday help computers store more data with less energy.

Phase change memory, a fast and durable form of data storage that operates differently from the memory in modern devices and does not require a continuous power source, may be well-suited for this material due to the observed structural modifications.

The research was made possible by a state-of-the-art X-ray diffraction system, valued at over $1 million, which was acquired in 2022 with funding from the Murdock Charitable Trust. This specialized equipment, located at WSU's Pullman campus, allows researchers to observe minute structural changes in the material as they happen. Such experiments typically require access to large national facilities, such as the Advanced Light Source at Berkeley National Laboratory in California.

Being able to do these high-pressure experiments on campus gave us the flexibility to really dig into what was happening. We discovered that the material did not just compress, it actually changed its internal structure in a big way.

Matt McCluskey, Professor and Study Co-Author, Department of Physics and Astronomy, Washington State University

The substance, known as β-ZnTe(en)_0.5, consists of layers of zinc telluride and ethylenediamine, an organic compound. McCluskey compares its composition to a sandwich.

McCluskey explained, “Imagine layers of ceramic and plastic stacked over and over. When you apply pressure, the soft parts collapse more than the stiff ones.”

Researchers used the new X-ray system and a diamond anvil cell, a device capable of applying extreme pressure, to observe that the material underwent two phase transitions at relatively low pressures (2.1 and 3.3 gigapascals). In both instances, the structure experienced a significant transformation, shrinking by as much as 8 %.

A phase transition occurs when a material changes its atomic structure, similar to how water turns into ice or steam, according to Julie Miller, the lead author of the study. In this case, the same atoms rearranged into a denser configuration during the transition between two solid states.

These transitions can significantly alter a material's physical properties, such as electrical conductivity or light emission. Phase change memory relies on the idea that different structural phases can be used to encode digital information because they often exhibit distinct electrical and optical properties.

Most materials like this need huge amounts of pressure to change structure, but this one started transforming at a tenth of the pressure we usually see in pure zinc telluride. That is what makes this material so interesting, it is showing big effects at much lower pressures.

Matt McCluskey, Professor and Study Co-Author, Department of Physics and Astronomy, Washington State University

Additionally, the researchers found that the material's behavior varies significantly depending on the direction of the applied pressure. Its layered structure and directional sensitivity make it more adaptable, enabling a broader range of potential applications.

Beyond memory, the material may have potential uses in photonics, a field that relies on light rather than electricity to transport and store data. The researchers suggest that because the material emits ultraviolet light, its glow may change depending on its phase, making it suitable for optical computing or fiber optics.

Although β-ZnTe(en)_0.5 is still in the early stages as a potential commercial memory material, this discovery represents a significant advancement.

We are just beginning to understand what these hybrid materials can do. The fact that we could observe these changes with equipment right here on campus makes it that much more exciting.

Matt McCluskey, Professor and Study Co-Author, Department of Physics and Astronomy, Washington State University

To develop a more detailed understanding of the material's behaviors and potential, the team will next examine its response to temperature changes and explore the effects of applying both pressure and heat.

The study was funded by the U.S. Department of Energy.

Journal Reference:

‌Miller, J. C., et al. (2025) Phase transitions of β-ZnTe(en)_0.5 under hydrostatic pressure. AIP Advances. doi.org/10.1063/5.0266352.