Application of mechanical spectroscopy to the study of high performance (Bi1-xSbx)2(Te1-ySey)3 extruded thermoelectric alloys

Decreasing the length of thermoelectric (TE) module legs results in a significant increase in power density, both for cooling applications and electricity generation. However, this reduction also results in a significant increase of mechanical stress in the legs materials. Thus, it is important to implement an effective method to characterize the mechanical properties, such as mechanical spectroscopy, which has so far not yet been applied to TE materials. High performance quaternary N- and P-type (Bi_1-xSb_x)₂(Te_1-ySe_y)₃ alloys, as well as Bi₂Te₃ N-type compounds were produced by mechanical alloying of pure elements following by hot extrusion. They were then characterized by mechanical spectroscopy, scanning electron microscopy, and electrical transport measurements. Free longitudinal and transverse oscillations with natural resonance frequencies in the kHz range were excited and fast Fourier transform analyzed for rod specimens with circular section 25 mm in diameter. This analysis provides quantitative information of the elastic properties of these materials, which we have correlated to transport and structural properties, such as porosity, texture, electrical conductivity and thermoelectric performance. We also provide results on several internal friction mechanisms of energy dissipation in TE alloys, which have been identified analyzing oscillation damping.