Abstract
The previous experimental work showed that Hf- or Zr-doping has remarkably improved the thermoelectric performance of FeNbSb. Here, the first-principles method was used to explore the possible reason for such phenomenon. The substitution of X (Zr/Hf) atoms at Nb sites increases effective hole-pockets, total density of states near the Fermi level (EF), and hole mobility to largely enhance electrical conductivity. It is mainly due to the shifting the EF to lower energy and the nearest Fe atoms around X atoms supplying more d-states to hybrid with X d-states at the vicinity of the EF. Moreover, we find that the X atoms indirectly affect the charge distribution around Nb atoms via their nearest Fe atoms, resulting in the reduced energy difference in the valence band edge, contributing to enhanced Seebeck coefficients. In addition, the further Bader charge analysis shows that the reason of more holes by Hf-doping than Zr in the experiment is most likely derived from Hf atoms losing less electrons and the stronger hybridization between Hf atoms and their nearest Fe atoms. Furthermore, we predict that Hf/Sn co-doping may be an effective strategy to further optimize the thermoelectric performance of half-Heusler (HH) compounds.
Highlights
Values of Ti/Zr-doped FeNbSb are smaller than that of Hf-doped FeNbSb, and the ZT of 14% Hf-doped FeNbSb can reach 1.5 at 1200 K
Our work shows that Hf-doping results in a higher hole mobility than Zr-doping by affecting on the valence band effective mass (m*) near the EF, and the nearest Fe atoms around Hf atoms supplying more d-states to hybrid with Hf d-states at the vicinity of the EF leads to the increased effective hole-pockets
From the further Bader charge analysis, we find that the stronger hybridization between Hf atoms and their nearest Fe atoms near the EF and the less lost electrons of Hf atoms possibly result in 15.625% Hf-doped FeNbSb supplying more holes than 15.625% Zr-doped FeNbSb
Summary
Edoped −756.322 −756.151 −749.842 −753.829 −472.780 −472.625 −468.866 −471.467. Our work shows that Hf-doping results in a higher hole mobility than Zr-doping by affecting on the valence band effective mass (m*) near the EF, and the nearest Fe atoms around Hf atoms supplying more d-states to hybrid with Hf d-states at the vicinity of the EF leads to the increased effective hole-pockets. From the further Bader charge analysis, we find that the stronger hybridization between Hf atoms and their nearest Fe atoms near the EF and the less lost electrons of Hf atoms possibly result in 15.625% Hf-doped FeNbSb supplying more holes than 15.625% Zr-doped FeNbSb. In addition, the charges are localized around Nb atoms near the Zr (or Hf) atoms in FeNb1−xZr/HfxSb (x = 0.10 and 0.15) systems, which likely leads to the reduced energy difference (⊿EA-M) in the valence band edge between the point A and M. We predict that the thermoelectric performance of FeNbSb can be largely increased by Hf/Sn co-doping
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