Professor Jong-Soo Rhyee's research team at the Department of Applied Physics has presented a new approach to significantly improve the thermal stability of thermoelectric materials

The thermoelectric effect refers to the phenomenon in which heat and electricity are converted to each other. Thermoelectric materials are eco-friendly energy conversion materials that convert heat into electricity and use it for power generation or use electricity to generate temperature differences to cool the surroundings. As of late, the performance index of thermoelectric materials has increased significantly, resulting in the launch of refrigerators incorporating thermoelectric effects. However, the problem of thermal instability of the material operating at high temperatures still remains to be resolved.

The research team headed by Professor Rhyee including Dr. Jin-hee Kim, and Dr. Jae-hyun Yoon took a different approach to the problem. With conventional thermoelectric materials, the silver-tellurium (Ag2Te) and antimony-tellurium (Sb2Te3) phases tend to separate at high temperatures, and electrons and holes become entangled, resulting in poor thermoelectric performance. The research team took advantage of this phase separation phenomenon and applied a thermal cycling process by quickly going back and forth between high temperature and room temperature under the condition that the phase separation was stabilized and there was no performance degradation. As a result, the particles of the thermoelectric material were thermally decomposed and stabilized. The metastable phase created in this process was thermally stabilized and showed stable characteristics thereafter. Professor Rhyee explained, “This is the result of increasing performance by exploiting the instability of the material.”

Increasing thermal stability and energy efficiency by exploiting the inherent instability of the material
High-efficiency thermoelectric modules with improved thermal stability increase energy efficiency through electrical energy conversion. This thermoelectric module is expected to contribute greatly to achieving carbon neutrality by allowing various new and renewable energies, such as solar heat, geothermal heat, and waste heat, to be converted into electricity more easily and efficiently. For example, if these thermoelectric modules are applied in a solar power generation system, more power can be produced by efficiently converting the solar heat absorbed during the day into electricity. This not only maximizes the efficiency of energy resources, but also reduces fossil fuel use and greatly contributes to environmental protection.

Changes in the industrial field are also expected. By converting waste heat generated from industrial machines or processes into electricity, energy loss can be minimized with a reduction in overall power consumption. The characteristics of thermoelectric materials allow them to be used even in extreme environments, so they are expected to be applied in a variety of fields.

Professor Rhyee, who led the research, explained the significance of the research and said, “We improved the thermal stability of thermoelectric materials in a quite simple way. This is a good result obtained through an out-of-the-box thinking.” He plans to continue to work on developing various application technologies utilizing the thermoelectric effect. This study was published in the May issue of Advanced Functional Materials, a world-renowned journal in the field of applied physics, under the title “Enhancement of Phase Stability and Thermoelectric Performance of Meta-Stable AgSbTe2 by Thermal Cycling Process.” The research was conducted with support from the National Research Foundation of Korea.