During the conversion of energy, a lot of heat is lost. It could even be as high as 70% according to some estimates. The thermoelectric materials at TU Wien can convert heat into electricity. This effect, known as the Seebeck effect, can be applied in many areas of industry and everyday life.

Ernst Bauer’s research group recently discovered a new thermoelectric material made of iron, vanadium, and aluminum. This is called Fe2VAl. Nature Communications published the results of these researchers.

The ideal thermoelectric

Researchers are searching for materials with a variety of properties to maximize energy conversion. This is difficult, however, because the properties of these materials are interrelated and interdependent. The researchers therefore asked what a material should look like in order to meet all of these conditions.

Physicists from TU Wien were able to find a solution to this paradox and optimize all thermoelectric properties of one material. “The Anderson transition, which is a quantum phase change from mobile to localized electron states, provides the ideal conditions for a thermoelectric. Fabian Garmroudi is the first author of this study.

When impurity atoms, which strongly bind their electrons, are added to semiconductors, the Anderson transition takes place. These are analogous to the sea ice floes that can be stepped on but are initially isolated from one another. Fabian Garmroudi makes a similar comparison. In solids, this is similar: If the number of impurity-atoms exceeds a critical level, electrons can move quickly from one atom and electricity can flow.

When it gets hot, the atoms swap places

In close collaboration with researchers from Japan, Sweden, and Austria, the Anderson transition was shown. It was also linked to a significant shift in thermoelectric properties. The exciting discovery was made by the team when they heated the material to extremely high temperatures, near the melting point.

“At high temperatures, atoms vibrate strongly so that they sometimes swap their lattice locations. Iron atoms can then be found where vanadium and other atoms used to be. This ‘atomic confusion’ occurs at high temperatures and can be frozen by so-called “quenching”, which is rapid cooling in a hot bath. Ernst Bauer reports. These irregular defects serve the exact same purpose as those impurity atoms, and without changing the material’s chemical composition.

Energy conversion due to disorder

Many areas of solid-state Physics research are interested in materials with ideal crystal structures and that are as pure as possible. This is because the regularity in the atoms makes it easier to describe the physical properties. However, in the case of Fe2VAl it is precisely these imperfections that are responsible for the thermoelectric performance. In neighboring fields, it has been proven that irregularities can be beneficial: “Basic research in quantum materials is an example of this.” Andrej Pustogow is one of the co-authors. “Science has already shown that disorder can be the essential spice in quantum soup.” This concept is also being used in applied solid state research.