High thermoelectric figure of merit by resonant dopant in half-Heusler alloys

Long Chen,Jian He,S Joseph Poon,Terry M Tritt,Yamei Liu

doi:10.1063/1.4986760

Long Chen, Jian He + Show 3 more

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https://doi.org/10.1063/1.4986760

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Journal: AIP Advances	Publication Date: Jun 1, 2017
Citations: 45	License type: cc-by

Affiliation: University of Virginia, Clemson University

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.

Highlights

Thermoelectric materials can directly convert heat to electricity and vice versa, making thermoelectrics an important component of the renewable energy technology
The performance of thermoelectric material is measured by the dimensionless figure of merit ZT, ZT = (S2σ/κ)T, where σ is the electrical conductivity, S is the Seebeck coefficient, κ is the total thermal conductivity
Among the state-of-the-art thermoelectric materials, the RNiSn (R = Hf, Zr and Ti) half-Heusler (HH) phases have been noted by their thermal stability,[1,2] scalability, and potential for large power output,[3,4,5,6] and the combination of high Seebeck coefficient and low thermal conductivity.[7,8,9,10,11,12]

Summary

Introduction

Thermoelectric materials can directly convert heat to electricity and vice versa, making thermoelectrics an important component of the renewable energy technology. High thermoelectric figure of merit by resonant dopant in half-Heusler alloys

Results

Conclusion