Temperature Dependent Structure Stability Studies on Thermoelectric Yb 0.025 Fe 0.3 Co 0.7 Sb 3
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Temperature Dependent Structure Stability Studies on Thermoelectric Yb0.025Fe0.3Co0.7Sb3 Mohsen Y. Tafti1, Mohsin Saleemi1,2, Mats Johnsson2, Alexandre Jacquot3, and Muhammet S. Toprak1 1 Department of Material and Nano-Physics, KTH Royal Institute of Technology, Stockholm Sweden. 2 Department of Materials and Environmental Chemistry, Stockholm University, Stockholm, Stockholm, Sweden 3 Fraunhofer Institute for Physical Measurements, Freiburg, Germany ABSTRACT Depending on their application temperature thermoelectric (TE) materials are classified in three main categories; as low (up to 250°C), intermediate (up to 550°C) and high (above 600°C) temperature. Currently, Skutterudites (CoSb3) based materials have shown promising results in the intermediate temperature range (300-500°C). This family of material is highly suitable for automotive, marine transportation and industrial power generation applications to recover the waste heat from the exhaust and generate electricity. Conventional TE modules need p- and n-type semiconductor materials and for the skutterudite family, iron (Fe) has proven to be among the best candidates for the substitution of cobalt sites. Additionally, rare earths are introduced as rattlers in the crystal cages of the skutterudite to decrease the thermal conductivity, thus improving the figure of merit ZT of the TE material. For practical application for device fabrication, stability of these materials is of great importance. Compositional stability is being addressed as the material decomposes above certain temperature. Temperature dependent x-ray diffraction study was performed on Fe substituted, Yb-filled skutterudites, using Beam Line I711 at MAX LAB, to observe the crystal structure as a function of temperature. Diffraction patterns were collected from room temperature up to 500°C by utilizing Huber furnace. The results show success in filling process showing almost 80% reduction of the thermal conductivity from bulk. Additionally the thermal expansion coefficient value was within the average value for skutterudites which proves practical application of this powder for industrial applications. INTRODUCTION Thermoelectric (TE) materials have shown promising results in sustainable energy development. Their dual property of inter-conversion between heat and electricity gives them a huge advantage considering they don’t need any extra moving parts or carriers. Skutterudites are a family of material with MX3 (where M is Co, Fe, Ni) and X is either P, Sb, or As [1-3]. They demonstrated promising TE performance in the intermediate temperature region (200~500℃). Therefore there have been intensive investigations regarding their fabrication and enhancement of properties. Additionally Skutterudites crystal structure accommodates 2 voids, which can be partially or fully filled with heavy or rare earth elements that provide extra scattering points for phonons, thus reducing their thermal conductivity. One of the rare earth elements which are widely used for this purpose is Yb [1-7]. To be able to use
