Vienna University of Technology (TU Wien,Vienna) scientists have now developed a completely new material with a ZT value of 5 to 6. It is so effective that it could be used to provide energy for sensors or even small computer processors.

Thermoelectric materials convert heat into electrical energy. The amount of energy that can be generated is measured by the so-called ZT value. The best thermoelectrics to date were measured at ZT values of around 2.5 to 2.8. The higher the ZT value of a material, the better its thermoelectric properties. This is due to the so-called Seebeck effect: If there is a temperature difference between the two ends of such a material, electrical voltage can be generated and current can start to flow.

The scientists have now succeeded in developing a completely new material with the ZT value raised to 5 to 6. It is a thin layer of iron, vanadium, tungsten and aluminum applied to a silicon crystal. Instead of connecting small electrical devices to cables, they could generate their own electricity from temperature differences.

The new material information has been published in the journal Nature.

Professor Ernst Bauer from the Institute of Solid State Physics at TU Wien said, “A good thermoelectric material must show a strong Seebeck effect, and it has to meet two important requirements that are difficult to reconcile. On the one hand, it should conduct electricity as well as possible; on the other hand, it should transport heat as poorly as possible. This is a challenge because electrical conductivity and thermal conductivity are usually closely related.”

Image Credit: Vienna University of Technology. Click image for the largest view.

At the Christian Doppler Laboratory for Thermoelectricity, which Professor Bauer established at TU Wien in 2013, different thermoelectric materials for different applications have been studied over the last few years. This research has now led to the discovery of a particularly remarkable material – a combination of iron, vanadium, tungsten and aluminum.

Bauer said, “The atoms in this material are usually arranged in a strictly regular pattern in a so-called face-centered cubic lattice. The distance between two iron atoms is always the same, and the same is true for the other types of atoms. The whole crystal is therefore completely regular.”

However, when a thin layer of the material is applied to silicon, something amazing happens: the structure changes radically. Although the atoms still form a cubic pattern, they are now arranged in a space-centered structure, and the distribution of the different types of atoms becomes completely random. “Two iron atoms may sit next to each other, the places next to them may be occupied by vanadium or aluminum, and there is no longer any rule that dictates where the next iron atom is to be found in the crystal,” explained Bauer.

This mixture of regularity and irregularity of the atomic arrangement also changes the electronic structure, which determines how electrons move in the solid. “The electrical charge moves through the material in a special way, so that it is protected from scattering processes. The portions of charge traveling through the material are referred to as Weyl Fermions,” explained Bauer. In this way, a very low electrical resistance is achieved.

Lattice vibrations, on the other hand, which transport heat from places of high temperature to places of low temperature, are inhibited by the irregularities in the crystal structure. Therefore, thermal conductivity decreases. This is important if electrical energy is to be generated permanently from a temperature difference – because if temperature differences could equilibrate very quickly and the entire material would soon have the same temperature everywhere, the thermoelectric effect would come to a standstill.

Bauer noted the high points of the progress, “Of course, such a thin layer cannot generate a particularly large amount of energy, but it has the advantage of being extremely compact and adaptable. We want to use it to provide energy for sensors and small electronic applications.”

The demand for such small-scale generators is growing quickly: In the “Internet of Things,” more and more devices are linked together online so that they automatically coordinate their behavior with each other. This is particularly promising for future production plants, where one machine has to react dynamically to another.

This significantly important progress in a very useful and rich field. An incredible amount of heat is just lost to the atmosphere that could be put to work. The promise now with a doubling of the ZT value looks way better than only a few weeks ago. A sincere thanks is noted and congratulations sent about the results.


1 Comment so far

  1. Andrew on December 17, 2019 4:38 AM

    Enjoyed reading the article above , really explains everything in detail,the article is very interesting and effective.Thank you and good luck for the upcoming articles.

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