NbFeSb-based p-type half-Heuslers for power generation applications

Abstract

We report a peak dimensionless figure-of-merit (ZT) of ∼1 at 700 °C in a nanostructured p-type Nb_0.6Ti_0.4FeSb_0.95Sn_0.05 composition. Even though the power factor of the Nb_0.6Ti_0.4FeSb_0.95Sn_0.05 composition is improved by 25%, in comparison to the previously reported p-type Hf_0.44Zr_0.44Ti_0.12CoSb_0.8Sn_0.2, the ZT value is not increased due to a higher thermal conductivity. However, the higher power factor of the Nb_0.6Ti_0.4FeSb_0.95Sn_0.05 composition led to a 15% increase in the power output of a thermoelectric device in comparison to a device made from the previous best material Hf_0.44Zr_0.44Ti_0.12CoSb_0.8Sn_0.2. The n-type material used to make the unicouple device is the best reported nanostructured Hf_0.25Zr_0.75NiSn_0.99Sb_0.01 composition with the lowest hafnium (Hf) content. Both the p- and n-type nanostructured samples are prepared by ball milling the arc melted ingot and hot pressing the finely ground powders. Moreover, the raw material cost of the Nb_0.6Ti_0.4FeSb_0.95Sn_0.05 composition is more than six times lower compared to the cost of the previous best p-type Hf_0.44Zr_0.44Ti_0.12CoSb_0.8Sn_0.2. This cost reduction is crucial for these materials to be used in large-scale quantities for vehicle and industrial waste heat recovery applications.