High Thermoelectric Figure of Merit by Resonant Dopant in Half-Heusler Alloys

TL;DR

This study demonstrates that resonant vanadium doping in half-Heusler alloys significantly enhances their thermoelectric figure of merit (ZT), achieving a record ZT of 1.3 near 850 K by increasing the Seebeck coefficient and reducing thermal conductivity.

Contribution

The paper provides a systematic investigation of vanadium as a resonant dopant in n-type half-Heusler alloys, revealing its unique role in boosting thermoelectric performance beyond previous doping strategies.

Findings

Vanadium doping increases Seebeck coefficient via resonant states.

Vanadium doping reduces thermal conductivity.

Achieved ZT of 1.3 near 850 K in optimized alloys.

Abstract

Half-Heusler alloys have been one of the benchmark high temperature thermoelectric materials owing to their thermal stability and promising figure of merit ZT. Simonson et al. early showed that small amounts of vanadium doped in Hf0.75Zr0.25NiSn enhanced the Seebeck coefficient and correlated the change with the increased density of states near the Fermi level. We herein report a systematic study on the role of vanadium (V), niobium (Nb), and tantalum (Ta) as prospective resonant dopants in enhancing the ZT of n-type half-Heusler alloys based on Hf0.6Zr0.4NiSn0.995Sb0.005. The V doping was found to increase the Seebeck coefficient in the temperature range 300-1000 K, consistent with a resonant doping scheme. In contrast, Nb and Ta act as normal n-type dopants, as evident by the systematic decrease in electrical resistivity and Seebeck coefficient. The combination of enhanced Seebeck coefficient due to the presence of V resonant states and the reduced thermal conductivity has led to a state-of-the-art ZT of 1.3 near 850 K in n-type (Hf0.6Zr0.4)0.99V0.01NiSn0.995Sb0.005 alloys.