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Mechanical spectroscopy measurements are reported on rods of (Bi1−xSbx)2Te3 and (Bi1−xSbx)2(Te1−ySey)3 polycrystalline thermoelectric (TE) composite alloys produced by mechanical alloying and hot extrusion. Low internal friction (Q−1) and large stiffness coefficients obtained in the 293–573 K range corroborate the improved elastic properties of these hot extruded and highly textured polycrystalline materials that have enhanced TE properties. Their stiffness shows a quadratic (decreasing) temperature dependence, and the value for most composites is larger than that of conventional single-phase random alloys and hot extruded bismuth telluride. One particular damping mechanism in Q−1, believed to be due to grain boundary motion, is thermally activated at temperatures higher than 420 K. The prefactor of the Arrhenius law correlates with the activation enthalpy (Δh) for every composite. It varies exponentially with Δh for more than six orders of magnitude for activation enthalpies up to 0.9 eV. The observation of this enthalpy–entropy compensation effect results from the existence of a maximum in energy dissipation in a linear regime of weak perturbations. This simple explanation is proposed to apply to this ubiquitous effect which has been observed in many areas of physics, chemistry, and biology. [ABSTRACT FROM AUTHOR]

Bulk nanocomposites of (Bi0.2Sb0.8)2Te3 and (Bi0.95Sb0.05)2(Te0.95Se0.05)3 containing MoS2 nano-inclusions were obtained by mechanical alloying and hot extrusion. The nano-inclusions are observed to decorate the grain boundaries of the matrix, leading to a significant reduction of average grain size and crystallite size compared to those of the conventional single phase alloy. Consequently, the thermal conductivity of these nanocomposites also decreases (~1.4W/m·K at 450K for 0.4wt.% MoS2) when compared to the conventional alloy (~1.8W/m·K). The structural changes in the nanocomposites obtained by mechanical spectroscopy in the temperature range 293-540K show an increase of the internal friction accompanied by a systematic reduction of its activation energy with an increase in MoS2 content. [ABSTRACT FROM AUTHOR]