Significantly improving thermoelectric module performance using a new material developed by NIMS

1. Mg₃Sb₂ is a thermoelectric compound composed of cheap and abundant elements. NIMS has successfully improved the thermoelectric performance of Mg₃Sb₂ by doping it with indium and precisely controlling the sintering duration. This approach resulted in substantially increased electronic conductivity while effectively reducing thermal conductivity. The Mg₃Sb₂-based material exhibited a very high figure of merit (zT) of approximately 2.0 at 723 K. In addition, a module made of this material achieved a thermoelectric conversion efficiency of approximately 12.6%—the highest efficiency ever recorded for a single-leg module. These results may greatly advance the development of practical thermoelectric devices.

2. Solid thermoelectric devices capable of directly converting waste heat into electricity are potentially effective technologies for achieving carbon neutrality and making society more sustainable. However, their wide use has been hindered by their inadequate thermoelectric performance, scarcity and high cost. Improving the performance of thermoelectric materials requires simultaneously maximizing their electric conductivity and minimizing their thermal conductivity. Despite decades of strategic efforts, only a few high-performance thermoelectric materials (e.g., GeTe, PbTe, AgSbTe₂ and SnSe) have achieved or exceeded a zT of 2.0. Moreover, commercial application of these materials is considered difficult due to their toxicity, high cost, the scarcity of their constituent elements, instability and/or other undesirable characteristics.

3. NIMS recently succeeded in creating an Mg₃Sb₂-based alloy microstructure with enhanced atomic-level structural ordering which is still capable of inducing intense phonon scattering. This was achieved by doping Mg₃Sb₂ with indium and precisely controlling the sintering duration. The improved atomic structural ordering enhanced electronic transport by reducing electron localization, while crystalline defects in the microstructure induced lattice distortions, limiting phonon transport. These effects synergistically improved the material's thermoelectric performance, achieving a zT of approximately 0.5 at room temperature, 2.0 at 723 K and an average of 1.36 across temperatures between 300 and 723 K—the highest values reported to date for an Mg₃Sb₂-based alloy. In addition, a single-leg module made of this material achieved an unprecedented thermoelectric conversion efficiency of approximately 12.6% (see the graphs).

4. These results demonstrate the feasibility of developing practical thermoelectric modules that contain virtually no scarce chemical elements, supporting their potential for widespread use. Such modules may serve as stand-alone power sources for the numerous sensors needed to put Japan’s Society 5.0 vision into practice, and also greatly contributing to energy savings. Furthermore, achieving the highest thermoelectric performance by reducing charge localization through enhanced band structure ordering may stimulate further research into controlling complex, defect-rich microstructures in thermoelectric materials.

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5. This project was carried out by Takao Mori (Group Leader, Thermal Energy Materials Group, Research Center for Materials Nanoarchitectonics (MANA), NIMS).
This work was conducted as part of a large-scale project entitled “Development of innovative thermoelectric materials and devices using magnetism” (project leader: Takao Mori) supported by the JST-Mirai Program.

6. This research was published in Nature Communications, an open access journal, on August 9, 2024.