A breakthrough discovery in thermoelectrics: Interpreting thermal conductivity with light

Breakthrough science is often the result of true collaboration, where researchers from different fields, different perspectives, and different experiences come together in a unique way.

This effort by researchers at Clemson University has led to a discovery that may change the way thermoelectric science advances.

Postgraduate research assistant Prakash Parajuli, research assistant professor Sriparna Bhattacharya and the founding director of the Clemson Nanomaterials Institute (CNI) Apparao Rao collaborated with an international team of scientists to use light to study an efficient thermoelectricity Material.

Their research has been published in the journal “Advanced Science” under the title “High zT and its origin in Sb-doped GeTe single crystals.”

Thermoelectric materials convert thermal energy into useful electrical energy; therefore, people are very interested in materials that can efficiently convert thermal energy. The key to measuring progress in this field is the merit value, denoted as zT, which is highly dependent on the properties of thermoelectric materials. Many thermoelectric materials exhibit a zT of 1-1.5, which also depends on the temperature of the thermoelectric material. Only recently have materials with a zT of 2 or higher been reported.

The team focused on studying the properties of germanium telluride (GeTe), which is a single crystal material, but ordinary GeTe without any doping does not show exciting properties. But once a little antimony is added to it, it can show good Electronic properties and very low thermal conductivity.

Although others have reported GeTe-based materials with high zT, these are polycrystalline materials. Polycrystals have boundaries between the many small crystals they form. Although such boundaries help hinder heat transfer, they obscure the origin of the basic process leading to high zT.

This low thermal conductivity is a surprise because the simple crystal structure of this material allows heat to flow easily throughout the crystal. The key is to block the flow of heat through quantitative lattice vibrations called phonons, while allowing electrons to flow.

This study found that adding an appropriate amount of antimony to GeTe can maximize electron flow and minimize heat flow. The presence of 8 antimony atoms in every 100 GeTe will generate a new set of phonons, thereby effectively reducing the heat flow, which has been confirmed experimentally and theoretically.

Together with the collaborators who grow crystals, in addition to density functional theory calculations, the team also performed electron and heat transfer measurements, and found this mechanism in two ways: first, by modeling, using heat transfer data; second, , Through Raman spectroscopy, detect the phonons inside the material.

A whole new perspective in thermoelectric research emerged: Scientists can now use light to decode the thermal conductivity of thermoelectric materials, and researchers realize that the results measured with light are very consistent with those found through heat transfer measurements. Future research on thermoelectrics should use light-this is a very powerful non-destructive method that can illuminate the heat transfer in thermoelectrics, illuminate the sample with light, and collect information to get accurate results without destroying the sample.

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