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.