The low and high temperature thermoelectric properties of Yb3Si5

Silicides have been of great interest for thermoelectric applications due to their abundant elements as well as thermal and chemical stability. In this paper, we examined the thermoelectric properties of Yb3Si5 polycrystalline samples in a wide temperature range from 10 to 800 K. The temperature dependence of the Seebeck coefficient was successfully analyzed by assuming a narrow 4f quasi-particle band, indicating the intermediate valence state of Yb2+-Yb3+ is responsible for the high power factor. A very large maximum power factor of similar to 4.70 mWm(-1)K(-2) was observed at 72 K and room temperature value similar to 1.56 mWm(-1)K(-2) for Yb3Si5. These results shows that Yb-Si compounds have large potential to be used as low temperature TE applications in the future. We also studied the Co-doping effect in Yb3Si5, namely, Yb3Co x Si5-x where x = 0, 0.1, 0.15, 0.20 and investigated their thermoelectric properties. While powder X-ray diffraction analysis confirmed all main peaks indexed to Yb3Si5 phase, SEM and EDX analyses revealed that Co is precipitated as metal particles, forming a composite material with Yb3Si5 phase. Thermoelectric properties of the Co-doped samples are also reported.