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The significance of the often observed kinetic compensation effect (KCE) remains controversial. The assumption of its validity, as well as its ubiquity, has led to speculations on its significance with no general consensus in the scientific community. Efforts to understand the KCE have usually attempted connections between microscopic events, structures, and mechanisms involved in various kinetic processes. An alternative proposition, with no relation to specific mechanisms, is presented suggesting that there is no new conceptual physics in the KCE. An analysis of internal friction (IF) in the framework of linear response to weak perturbations highlights that the concomitant energy dissipation cannot exceed a maximum or peak value which depends solely on the anelastic properties of the material. The KCE is shown to be a consequence of this simple fact. This physical principle underpinning the KCE is able to explain its ubiquity because of its general nature beyond any specific kinetic rate mechanism. Examples of IF in different systems such as polycrystalline thermoelectric composites and Al bicrystals, which show evidence of the KCE, conform to this prediction. While the observation on Al bicrystals has previously been presented and interpreted as signaling a phase transition, the analysis presented here demonstrates the simpler alternative. A similar argument is presented to derive the KCE in the thermal desorption of gases, which involves kinetic processes unrelated to the above examples. It is proposed that a KCE can, in general, be deduced for any set of closely related relaxation processes having close peak values of energy dissipation. [ABSTRACT FROM AUTHOR]

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]