Long-term stability of phase-separated half-Heusler compounds

Abstract

Half-Heusler (HH) compounds have shown high figure of merit up to 1.5. Here, we address the long-term stability of n- and p-type HH materials. For this purpose, we investigated HH materials based on the Ti_0.3Zr_0.35Hf_0.35NiSn-system after 500 cycles (1700 h) from 373 to 873 K. Both compounds exhibit a maximum Seebeck coefficient of |α| ≈ 210 μV K⁻¹ and a phase separation into two HH phases. The dendritic microstructure is temperature resistant and upon cycling the changes in the microstructure are so marginal that the low thermal conductivity values (κ < 4 W m⁻¹ K⁻¹) could be maintained. Our results emphasize that phase-separated HH compounds are suitable low cost materials and can lead to enhanced thermoelectric efficiencies beyond the set benchmark for industrial applications.