New hybrid materials boost energy conversion by 100 percent

An international research team has developed new, highly efficient thermoelectric materials that have the potential to compete with current state-of-the-art compounds, while offering enhanced stability and significantly lower production costs.

Led by Fabian Garmroudi, PhD, a Director’s Postdoctoral Fellow at Los Alamos National Laboratory (USA), the research team successfully developed hybrid materials that simultaneously suppress lattice vibrations and enhance charge carrier mobility by employing a novel approach.

The innovation, according to Garmroudi, lies in combining two materials with fundamentally different mechanical properties but similar electronic traits.

The idea behind the study emerged from the potential of thermoelectric materials to directly convert heat into electrical energy, making them especially appealing for the growing Internet of Things – particularly for powering microsensors and other miniature electronic components autonomously.

To improve their efficiency, it is essential to simultaneously suppress heat transport through lattice vibrations and enhance electron mobility, a challenge that has long impeded progress in the field.

Unlocking unknown properties

Efficient thermoelectric materials – solid-state semiconductors that transform heat into electric power- need to conduct electricity efficiently while minimizing heat transfer. This, however, presents a challenge on its own, as materials that conduct electricity well typically also conduct heat effectively.

“In solid matter, heat is transferred both by mobile charge carriers and by vibrations of the atoms in the crystal lattice,” Garmroudi says, emphasizing that researchers have devised advanced techniques to engineer thermoelectric materials with exceptionally low thermal conductivity over the past few decades.

“In thermoelectric materials, we mainly try to suppress heat transport through the lattice vibrations, as they do not contribute to energy conversion,” he adds.

Garmroudi recalls developing the novel hybrid materials during his research stay in Tsukuba, Japan, supported by the Lions Award and carried out at the National Institute for Materials Science as part of his work at TU Wien (Vienna University of Technology).

Under intense heat and pressure, he fused two distinct powders, one made from an iron-based alloy with vanadium, tantalum, and aluminum (Fe₂V_0.95Ta_0.1Al_0.95), and the other from a bismuth-antimony mix (Bi_0.9Sb_0.1). The result was a compact hybrid material with promising thermoelectric potential.

Additionally, because of their differing chemical and mechanical characteristics, the two materials did not blend on the atomic scale. Instead the bismuth-antimony component selectively accumulated at the micrometer-sized interfaces between the crystals of the FeVTaAl alloy.

Separating heat and electricity flow

According to Garmroudi, the two materials have vastly different lattice structures, which means their allowed quantum lattice vibrations don’t align. As a result, thermal vibrations can’t easily pass from one crystal to the other, significantly limiting heat transfer at their interfaces.

Because the two materials share similar electronic properties, charge carriers not only move freely but also accelerate significantly at the interfaces, the reason being that the BiSb component forms a topological insulator phase, a quantum state that blocks conduction inside while enabling nearly lossless surface transport.

“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,” concludes Garmroudi in a press release, adding that the targeted decoupling of heat and charge transport enabled the team to increase the efficiency of the material by more than 100 percent.

Bismuth telluride, introduced in the 1950s, is still regarded as the benchmark for thermoelectric materials today. However, the new hybrid materials offer a major advantage in being significantly more stable and more cost-effective.