Enhancing the thermoelectric performance of a p-type half-Heusler alloy, HfCoSb by incorporation of a band-matched chalcogenide, Cu2Te

Abstract

The figure-of-merit of p-type half-Heusler alloys is low due to high effective charge carrier mass and concentration. To offset this decrease a composite strategy has been adopted wherein a modified HfCoSb alloy and Cu₂Te based chalcogenide have been selected as two p-type components. The composites with a maximum of 25 wt% chalcogenide have been synthesized by spark plasma sintering. The components retain their structure and composition with the half-Heusler alloy having a cubic F3m structure while the chalcogenide has a predominantly hexagonal structure. The power factor of the 25 wt% composite increases to 1.2 mW m⁻¹ K⁻² with a concurrent decrease in the thermal conductivity to 1.8 W m⁻¹ K⁻¹ compared to 0.4 W m⁻¹ K⁻² and 2.8 W m⁻¹ K⁻¹ for the half-Heusler alloy, respectively. This results in the composite exhibiting the highest figure-of-merit of 0.65 compared to 0.15 for the half-Heusler alloy at 1023 K, an increase of 320%. The leg power output increases from 0.3 W cm⁻² to 0.65 W cm⁻² while the efficiency increases from 1.5% to 5.5% at this temperature. These enhancements are due to band matching and bending at the half-Heusler/chalcogendie interfaces which facilitates charge transport while blocking the phonons.