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Thermoelectric materials facilitate the direct transformation of heat into electrical energy, positioning them as pivotal components in the evolving “Internet of Things.” They hold particular promise for providing autonomous energy sources for microsensors and other diminutive electronic devices. Enhancing the efficiency of these materials necessitates a reduction in heat transport via lattice vibrations while simultaneously boosting electron mobility—a dual challenge that has often proven to be a barrier in research.
An international research team, led by Fabian Garmroudi, has made significant strides by employing an innovative approach to develop hybrid materials that successfully address both these challenges: reducing the coherence of lattice vibrations and enhancing charge carrier mobility. Their findings are documented in the journal Nature Communications.
Innovative combinations yield new properties
Effective thermoelectric materials must balance high electrical conductivity with low thermal conductivity, a seemingly paradoxical requirement, as materials that excel in electrical conduction typically also conduct heat well.
“Heat within solid materials is conveyed by both mobile charge carriers and atomic vibrations in the crystal lattice. Our primary focus in thermoelectric materials is to mitigate heat transport through lattice vibrations, as these do not contribute to energy conversion,” explains Garmroudi, who obtained his doctorate at TU Wien and is currently a Director’s Postdoctoral Fellow at Los Alamos National Laboratory in the U.S. Over the past few decades, advancements in materials research have introduced sophisticated techniques aimed at developing thermoelectric materials that exhibit extremely low thermal conductivity.
“With the support of the Lions Award, I was able to devise new hybrid materials at the National Institute for Materials Science in Japan that display outstanding thermoelectric characteristics,” Garmroudi reflects on his research tenure in Tsukuba, Japan, associated with his postdoctoral work at TU Wien. Specifically, he combined a powder of an alloy composed of iron, vanadium, tantalum, and aluminum (Fe2V0.95Ta0.1Al0.95) with a powder of bismuth and antimony (Bi0.9Sb0.1) and subjected the mixture to high pressure and temperature to form a compact material. However, due to their disparate chemical and mechanical properties, the two components do not fully amalgamate at an atomic level. Instead, the BiSb phase preferentially accumulates at the micrometer-sized boundaries between the FeVTaAl alloy crystals.
Separating heat and charge transport
The distinct lattice structures and accordingly varied quantum mechanically allowed lattice vibrations of the two materials hinder the transfer of thermal vibrations from one crystal to the other. As a result, heat transfer is substantially restricted at the interfaces. Conversely, the movement of the charge carriers remains largely unobstructed, and can even be significantly accelerated along these interfaces. This improvement is attributed to the emergence of a topological insulator phase in the BiSb material—a unique class of quantum materials that remain insulating internally while permitting almost loss-free charge transport on their surfaces.
This deliberate separation of heat and charge transport has enabled the research team to enhance the efficiency of the material by over 100%. “This progress significantly brings us closer to achieving a thermoelectric material that can rival commercially available options, such as those based on bismuth telluride,” states Garmroudi. The latter was developed in the 1950s and is still regarded as the benchmark for thermoelectric performance. Notably, the new hybrid materials offer greater stability and cost-effectiveness, representing a substantial advancement in the field.
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