Enhancement of Thermoelectric Figure of Merit of p‐Type Nb_0.9Ti_0.1FeSb 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 Nb 0.9 Ti 0.1 FeSb 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 Nb 0.9 Ti 0.1 FeSb shows an %20% higher zT value at 1073 K than the non-nanostructured one, mainly due to the effective reduction of the thermal conductivity.

Advances in half-Heusler alloys for thermoelectric power generation

“…Perhaps the most impressive feature of this family is the ability to achieve extremely large S 2 σ between 5 -6 mW.m -1 .K -1 over a wide temperature range. [46][47][48][121][122][123] As first reported in 2016, careful processing allows for S 2 σ 300 K > 10 mW.m -1 .K -2 to be achieved in Nb 0.95 Ti 0.05 FeSb, using a hot pressing temperature of 1100 °C to eliminate the parasitic electrical resistance from grain boundary scattering observed with lower SPS temperatures, as illustrated in Figure 5. 99 This was later also demonstrated for the analogous systems with Zr and Hf dopants.…”