Led by Saeed S. I. Almishal, a research professor of materials science and engineering at Penn State, a team of researchers has demonstrated that reducing oxygen during ceramic synthesis can unlock entire classes of materials previously considered impractical to make. By carefully controlling the oxygen environment inside a tube furnace, the group synthesized seven new high-entropy oxide ceramics, showing that stability in these complex systems can be achieved through deliberate thermodynamic control rather than trial and error.
Almishal, S. S. I., Furst, M., Tan, Y., Sivak, J. T., Bejger, G., Petruska, J., Ayyagari, S. V. G., Srikanth, D., Alem, N., Rost, C. M., Sinnott, S. B., Chen, L.-Q., & Maria, J.-P. (2025). Thermodynamics-inspired high-entropy oxide synthesis. Nature Communications, 16(1), 8211. https://doi.org/10.1038/s41467-025-63567-z
High-entropy oxides are ceramics made from five or more metal elements combined into a single crystalline phase. Their appeal lies in the way chemical disorder can produce useful mechanical, electrical, thermal, or magnetic behavior. At the same time, this disorder makes them difficult to synthesize. Many theoretically interesting compositions fail because certain metals shift into unwanted oxidation states under normal oxygen-rich conditions, destabilizing the crystal structure before it can fully form.
Saeed S. I. Almishal from Penn State stated,
“I am so grateful for the opportunities that I have had on this project and to be involved in every step of the research and publication process. Being able to present this material to a broad audience as an invited talk reflects my involvement and the excellent guidance I have received from my mentors. It means a lot to me to develop important communication skills as an undergraduate student, and I look forward to pushing myself further in the future!”
The Penn State team addressed this problem by treating oxygen as an active design parameter. Instead of firing samples in ambient air, they reduced the oxygen partial pressure during synthesis. This approach allowed iron and manganese, two elements that commonly over-oxidize, to remain in the 2+ oxidation state required for a stable rock salt structure. Under typical conditions, these elements would continue absorbing oxygen and disrupt the formation of a single-phase ceramic.
The researchers first demonstrated the concept using a composition containing magnesium, cobalt, nickel, manganese, and iron. Once stability was confirmed, they expanded the method to identify additional viable compositions. Machine learning tools were used to screen large numbers of possible metal combinations based on thermodynamic constraints, narrowing the search to systems likely to remain stable when oxygen availability was limited. Six additional compositions were then synthesized experimentally, all forming dense bulk ceramic pellets.
Rather than relying on empirical tuning, the study framed high-entropy oxide synthesis around fundamental thermodynamic principles. The key insight was that oxidation state control could be achieved by limiting how much oxygen the material is allowed to absorb during firing. By doing so, the researchers were able to guide multiple metal species into a shared crystal structure that would otherwise be inaccessible.
To verify that iron and manganese remained in the intended oxidation states, the team collaborated with researchers at Virginia Tech. Advanced X-ray absorption measurements were used to probe the electronic structure of the elements within the ceramics. The results confirmed that the reduced-oxygen strategy consistently stabilized the target oxidation states across all seven materials.
The findings are relevant beyond the specific compositions reported. High-entropy oxides are being investigated for applications in energy storage, electronics, catalysis, and protective coatings. A clear framework for stabilizing challenging compositions could shorten development cycles and expand the range of functional ceramics available for engineering use.
The researchers plan to further characterize the new materials, including testing their magnetic behavior, which is of particular interest given the presence of multiple transition metals. More broadly, the same oxygen-control approach may be applied to other oxide systems that have been considered unstable under conventional synthesis conditions.
The project also involved significant contributions from undergraduate researchers who participated in processing, fabrication, and characterization of the samples. Their involvement highlights how fundamental advances in materials science often emerge from collaborative laboratory work that bridges theory, computation, and experiment.
Overall, the study demonstrates that simplifying synthesis conditions can sometimes lead to more complex and useful outcomes. By removing oxygen at the right moment and in the right amount, the Penn State team showed that new regions of ceramic design space are not only theoretically interesting but experimentally reachable.
Adrian graduated with a Masters Degree (1st Class Honours) in Chemical Engineering from Chester University along with Harris. His master’s research aimed to develop a standardadised clean water oxygenation transfer procedure to test bubble diffusers that are currently used in the wastewater industry commercial market. He has also undergone placments in both US and China primarely focused within the R&D department and is an associate member of the Institute of Chemical Engineers (IChemE).
