Thermoelectrics

Small band gap semiconducting C1b compounds such as TiNiSn and CoTiSb are ideal materials for new thermoelectric modules. These compounds show high figure of merit (ZT>1), are available as p and n-type semiconductors, cheap and non toxic. However new materials can be designed using more than 250 semiconductor combination candidates subject to the following characteristics:
1. Environmental friendliness and compliance with laws and regulations
2. Low cost and guaranteed future availability of raw materials.
3. High efficiency (integral average ZT values higher than 1 up to 800°C).
4. Operating temperature range of up to 700°C.
5. TE materials pairs (n- & p-type) with very similar coefficients of thermal expansion and good thermoelectric compatibility.
6. Possibility of industrial processing.
There are no currently available thermoelectric materials that fulfil all of these requirements. However, C1b materials class does meet nearly all of the requirements, including a high power factor. A general challenge in improving the C1b materials is to reduce the comparatively high thermal conductivity to the order of about 10 Wm-1K-1. To tackle the challenging goal of approaching a ZT~3, the thermal conductivity will be decreased by a factor of 5 using different techniques of nano-structuring. The concept of Functionally Graded Materials (FGM) and segmentation will be used to achieve a higher power factor values over the entire TEC temperature range of operation (Patent submitted with BOSCH).

 

Key papers and collaborators

Thermoelectric properties of CoTiSb based compounds, Joachim Barth, Benjamin Balke, Gerhard H. Fecher, G. H. Fecher, H. Stryhanyuk, A. Gloskovskij, S. Naghavi, and Claudia Felser, J. Phys. D: Appl. Phys. 42 (2009) 185401

 

International Collaborations

A. Weidenkaff, EMPA Zürich, J. Snyder, Caltech, Y. Gelbstein, Israel, M. Rosseinsky, Liverpool

 

Industrial Collaborations

Bosch, Stuttgart, BASF, Ludwigshafen, Isabellen Hütte, Dillenburg, Fraunhofer Institut, Freiburg Xiaoliang Qi and Shou-Cheng Zhang, Stanford University, L. Molenkamp, H. Buhmann, Würzburg, S.S.P. Parkin, IBM, Almaden