Thermoelectric materials convert heat directly into electricity. Achieving high efficiency in these materials requires suppressing heat flow through lattice vibrations while maintaining; or even boosting, the mobility of charge carriers. Until now, efforts to reduce phonon transport have often compromised electrical performance. A new study by an international collaboration, led by Fabian Garmroudi of Vienna University of Technology and Los Alamos National Laboratory. The research, published in Nature, can be found here:
Garmroudi, F., Serhiienko, I., Parzer, M., Ghosh, S., Ziolkowski, P., Oppitz, G., Nguyen, H. D., Bourgès, C., Hattori, Y., Riss, A., Steyrer, S., Rogl, G., Rogl, P., Schafler, E., Kawamoto, N., Müller, E., Bauer, E., de Boor, J., & Mori, T. (2025). Decoupled charge and heat transport in Fe2VAl composite thermoelectrics with topological-insulating grain boundary networks. Nature Communications, 16(1), 2976. https://doi.org/10.1038/s41467-025-57250-6
The team begins with a Heusler‐type alloy powder—Fe₂V₀.₉₅Ta₀.₁Al₀.₉₅—and a powder of bismuth‐antimony (Bi₀.₉Sb₀.₁), known for its topological insulator properties. Pressing these powders together under high temperature and pressure creates a composite in which the Bi–Sb phase localises at grain boundaries rather than forming a uniform solid solution. Fabian Garmroudi, a Director’s Postdoctoral Fellow at Los Alamos National Laboratory (U.S.) and lead authors stated:
“In solid matter, heat is transferred both by mobile charge carriers and by vibrations of the atoms in the crystal lattice. In thermoelectric materials, we mainly try to suppress heat transport through the lattice vibrations, as they do not contribute to energy conversion,”
Simultaneously, electrons and holes move along Bi–Sb “surface” networks that act as conductive channels, benefiting from the material’s topological‐insulator character to reduce scattering losses. The result: a measured increase in electrical mobility (μₑ) alongside a marked drop in κₗ—a rare coupling of two normally opposing attributes.
Testing across a range of temperatures revealed that the hybrid material more than doubles the thermoelectric figure of merit (zT) compared to the base Heusler alloy. The team reports over a 100% improvement in conversion efficiency, bringing performance within reach of commercial bismuth‐telluride systems that have dominated the field since the 1950s. Moreover, the composite offers enhanced thermal and mechanical stability, along with potentially lower raw‐material costs.
By localizing the Bi–Sb phase to grain boundaries, bulk properties remain tunable via composition and interface engineering. Garmroudi said:
“This brings us a big step closer to our goal of developing a thermoelectric material that can compete with commercially available compounds based on bismuth telluride,”
Efficient thermoelectrics can recover waste heat from engines, industrial processes, and even body heat, feeding small electronics without batteries. The hybrid composites improved stability and reduced reliance on expensive tellurides could lower barriers to deployment in harsh environments. As sensor networks proliferate, local power autonomy becomes critical; materials that convert ambient temperature gradients into reliable electrical output will lead to new paradigms in distributed monitoring.
Leading the effort was Fabian Garmroudi alongside co-authors Illia Serhiienko, Hieu Duy Nguyen, Cédric Bourgès, Yuya Hattori, Naoyuki Kawamoto, and Takao Mori of the National Institute for Materials Science in Tsukuba, Japan. From Vienna University of Technology, the team included Michael Parzer, Alexander Riss, and Sebastian Steyrer, while the German Aerospace Center (DLR) contributed Sanyukta Ghosh, Pawel Ziolkowski, and Gregor Oppitz. The University of Vienna group comprised Gerda Rogl, Peter Rogl, Erhard Schafler, and Ernst Bauer, and the consortium was rounded out by Johannes de Boor.
Hassan graduated with a Master’s degree in Chemical Engineering from the University of Chester (UK). He currently works as a design engineering consultant for one of the largest engineering firms in the world along with being an associate member of the Institute of Chemical Engineers (IChemE).
