Enhanced Thermoelectric Performance of ZrTaNiSn Half-Heusler Alloys by Diagonal-Rule Doping.

Although Sb doping is regarded as the most effective method to regulate the carrier concentration within the optimum range for ZrNiSn-based half-Heusler (HH) alloys, the resulting thermal conductivity remains high. Hence, the aim of this study was to investigate the effect of "diagonal-rule" doping; that is, the Zr site was displaced by Ta, which can simultaneously enhance the electrical conductivity and reduce the lattice thermal conductivity. The solid-solubility limit of Ta in the ZrNiSn matrix was determined to be = 0.04. The highest , 0.72, was achieved at 923 K for ZrTaNiSn. In addition, increased by 10.2% for ZrTaNiSn compared with that for ZrNiSnSb at 873 K, which was mainly attributed to the reduced lattice thermal conductivity of ZrTaNiSn. These results suggest that Ta doping is more effective than Sb doping in ZrNiSn-based HH alloys. In addition, the microhardness of ZrTaNiSn was substantially improved with increasing Ta content and was also much higher than that of other traditional thermoelectric materials.