Enhanced Thermoelectric Performance in Hf-Free p-Type (Ti, Zr)CoSb Half-Heusler Alloys
High thermal conductivity and exorbitant cost of Hf has for a long time limited the prospects of half-Heusler (HH) alloys for applicability in thermoelectric (TE) energy conversion devices. This work demonstrates the implication of nanostructuring and efficacy of p-type acceptor dopant in (Ti,Zr)CoSb based HH alloys for enhancing the figure of merit (ZT) while eliminating the use of Hf. A series of (Ti,Zr)CoSb1−x(Si,Sn)x HH composition was synthesized using arc-melting and consolidated employing spark plasma sintering (SPS). The optimal doping of acceptor dopants, namely, Si and Sn significantly improves the power factor and strengthens the phonon scattering resulting in an enhanced TE performance with maximum ZT of 0.26 and 0.5 at 873 K, obtained for TiCoSb0.8Sn0.2 and ZrCoSb0.8Sn0.2, respectively. For further optimization, microstructural modifications by fine-tuning of the Ti to Zr ratio induces strain field effects and mass fluctuation in (Ti,Zr)CoSb0.8Sn0.2 compositions, which remarkably introduces additional phonon scattering resulting in maximum ZT ∼ 0.8 at 873 K for the best performing Zr0.5Ti0.5CoSb0.8Sn0.2 compound. The current study provides a better understanding of p-type dopants in HH materials by which prospective high TE performance can be obtained in low-cost Hf-free p-type (Ti,Zr)CoSb half-Heusler alloys.
KeywordsThermoelectric p-type half-Heuslers doping
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The authors acknowledge the financial support from BRNS, India (Ref No: 37(3)/14/22/2016-BRNS) and UTAP-EXPL/CTE/0050/2017. Author N.S.C. acknowledges CSIR, India (Grant no: 31/001(0430)/ 2014-EMR-1) for financial support. The technical support rendered by Mr. R. Shyam, and Mr. N. K. Upadhyay is also gratefully acknowledged.
Conflict of interest
There is no conflict of interest to declare.
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