Grain boundary Kapitza resistance analysis of nanostructured FeSb2

• We investigate grain size dependence of thermal conductivity of FeSb2 nanocomposites.
• Important features of thermal conductivity vs. temperature curve are explained.
• Interfacial thermal resistance plays an important role.
• Nanostructuring is very effective to reduce thermal conductivity of FeSb2.

We apply the effective medium approach model to determine the Kapitza resistance across the grain boundaries of nanostructured FeSb2 samples. A Kapitza resistance of 2.17 × 10−7 m2K W−1 at 10 K is observed. The results suggest a competition between the bulk thermal resistance and the Kapitza resistance. The suppression and peak shifting of the thermal conductivity to a higher temperature are caused by the large Kapitza resistance due to the decreasing grain-size in the nanocomposite. A large value of Kapitza length (Lk) of 390 nm at 10 K is also observed. Based on the results, it is proposed that nanostructuring could be a viable approach to improve thermoelectric properties of FeSb2.