Thermal expansion properties of thermoelectric generating device component

We investigated the thermal expansion properties of a component in order to develop a thermoelectric generating device using a Pb-Te system comprising PbTe doped with 0.5 wt%PbI₂ and Pb_0.5Sn_0.5Te, which were selected for n- and p-type legs, respectively, and Ni and Fe, which were selected for the electrodes. [1] The dependence of the thermal expansion coefficient on the crystal grain size of the leg materials was measured. The coefficients of thermal expansion of sintered Pb_0.5Sn_0.5Te and PbTe doped with 0.5 wt%PbI₂ with a powder grain size greater than 25 mum in the temperature range from 373 to 773 K were approximately 2.0 times 10^-5 /K and 1.9 times 10^-5 /K, respectively. For a powder grain size less than 25 mum, the coefficients increased rapidly by 10 times above 623 K. The coefficients of thermal expansion of sintered Ni and Fe were larger than those of casting Ni and Fe, respectively, and exhibited a reduction with the holding time.