How nanoparticles can change the figure of merit, ZT, and mechanical properties of skutterudites

Although filled Sb-based skutterudites have a high figure of merit, ZT, a successful route to further increase ZT is the incorporation of homogeneously dispersed nanoparticles into the thermoelectric matrix and this way to reduce the lattice thermal conductivity leaving the electrical resistivity and the Seebeck coefficient almost unchanged. In this paper we present a critical summary of literature data concerning the preparation methods and the change of ZT in skutterudite composites with oxides, metals, intermetallics, antimonides, nitrides, borides, tellurides, silicides and carbon based materials. As good mechanical properties are substantial for all TE applications, the influence of nanoparticles, dispersed in the skutterudite matrix, on the hardness, elastic moduli, fracture toughness, compressive and flexural strength is discussed in this paper and compared to other thermoelectric materials. Long-term durability of thermoelectric modules, built with p- and n-type materials, essentially depends on matching coefficients of thermal expansion of each leg-type material in the temperature gradient used. In case of skutterudites, it is well known that p-type skutterudites have generally a higher thermal expansion coefficient (CTE) than their n-type counterpart. We show that dispersed borides can reduce the CTE of p-type and enhance the CTE of n-type skutterudites. (c) 2017 Elsevier Ltd. All rights reserved.