Enhancement of Thermoelectric Figure of Merit of p‐Type Nb0.9Ti0.1FeSb Half‐Heusler Compound by Nanostructuring

Abstract

Half‐Heusler compounds with 18 valence electron count show a large thermoelectric power factor. However, the thermal conductivity is high, so if the thermal conductivity can be reduced, the thermoelectric figure of merit zT can be enhanced. The key point to reduce the thermal conductivity is effective phonon scattering. Nanostructuring is a well‐known method of introducing phonon scattering centers by creating high‐density grain boundaries in nanoscale. Herein, NbFeSb, which is one of the best p‐type half‐Heusler compounds in thermoelectrics, is focused on. Nanostructured bulk Nb0.9Ti0.1FeSb is synthesized by melt spinning followed by spark plasma sintering. The cooling speed during melt spinning is changed to obtain nanostructures with different sizes. This study reveals that the zT at high temperatures is enhanced by nanostructuring. The nanostructured Nb0.9Ti0.1FeSb shows an ≈20% higher zT value at 1073 K than the non‐nanostructured one, mainly due to the effective reduction of the thermal conductivity.