A novel valence-balanced double half-Heusler Ti2Zr2Hf2NbVFe5Ni3Sb8 alloy by high entropy engineering

The lattice thermal conductivity of stable 18-electron Ti2FeNiSb2 compound is remarkably lower than that of the traditional ternary half-Heusler alloy, and it is considered a promising thermoelectric material. Owing to the distinctive performance of high entropy alloys, we designed a novel valence-balanced double half-Heusler Ti2Zr2Hf2NbVFe5Ni3Sb8 alloy with high entropy sublattice. The experimental results showed that enhanced electrical transport properties and reduced thermal conductivity of the alloy were achieved. The thermal con-ductivity at room temperature was two fifths of that of reported Ti2FeNiSb2 and the maximum power factor improved three times. The ultralow theoretical minimum lattice thermal conductivity was estimated to be less than 0.2 W m- 1K-1, showing the possibility for further reduction. Phonon spectrum calculation showed that the high entropy strategy was valid for scattering phonons and limiting lattice thermal conductivity. A peak ZT-0.027 at 823 K was achieved, which is almost five times that of the Ti2FeNiSb2. This work demonstrates the effectiveness of the high entropy strategy in double half-Heusler compounds and the potential of the new concept of HE-DHH compounds as high-performance thermoelectric materials.