High figure of merit in (Ti,Zr,Hf)NiSn half-Heusler alloys

High-performance thermoelectric half-Heusler alloys with nominal compositions of Ti0.37Zr0.37Hf0.26NiSn were investigated. Scanning electron microscopy compositional mapping showed a remarkable separation of Ti and Zr + Hf rich phases, while Ni and Sn are homogeneously distributed. Additionally, a nanoscale phase separation of different half-Heusler phases was observed. The thermoelectric properties of the compounds were measured at 2 K < T < 900 K and showed a high figure of merit, reaching a value of ZT = 1 at 725 K.