Influence of silver nanoparticle addition,porosity, and processing technique on the mechanical properties of Ba0.3Co4Sb12 skutterudites

The thermoelectric skutterudite Ba_0.3Co₄Sb₁₂ is a promising candidate for waste heat recovery applications. Recently, it was demonstrated that the addition of silver nanoparticles (Ag_NP) to Ba_0.3Co₄Sb₁₂ increases both the thermoelectric figure of merit and electrical conductivity. This study is the first to examine the effect of Ag_NP addition on the material’s mechanical properties. This study also found that the Young’s modulus, E, shear modulus, G, and bulk modulus, B, decreased linearly with increasing volume fraction porosity, P. Resonant ultrasound spectroscopy was employed to measure the elastic moduli, and Vickers indentation was used to determine the hardness, H, and fracture toughness, K _C. Trends in the mechanical properties as a function of grain size, porosity, and the Ag_NP are discussed in terms of the pertinent literature. While K _C was independent of Ag_NP addition, porosity, and grain size, both E and H decreased linearly with increasing porosity. In addition, this study is the first to identify (i) the Ag₃Sb phase formed and (ii) the enhanced densification that occurs when the Ag_NP is sintered with Ba_0.3Co₄Sb₁₂ powders, where both effects are consistent with the eutectic and peritectic reactions observed in the binary phase diagram Ag–Sb. These eutectic/peritectic reactions may also be linked to the enhancement of electrical conductivity previously observed when Ag is added to Ba_0.3Co₄Sb₁₂. Also, similar beneficial eutectic/peritectic reactions may be available for other systems where conductive particles are added to other antimonides or other thermoelectric systems.