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Origin of high thermoelectric performance of FeNb 1 − x Zr/Hf x Sb 1 − y Sn y alloys: A first-principles study

View Article: PubMed Central - PubMed

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.

No MeSH data available.


Calculated total and partial density of states of Hf atoms for 15.625% Hf-doped FeNbSb (a) and the total nearest Fe states of X (Zr/Hf) atoms for 15.625% X-doped FeNbSb (b).
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f8: Calculated total and partial density of states of Hf atoms for 15.625% Hf-doped FeNbSb (a) and the total nearest Fe states of X (Zr/Hf) atoms for 15.625% X-doped FeNbSb (b).

Mentions: In addition, to deeply study the influence of different dopants (Zr/Hf) and different doping contents, we calculated the partial charge densities of FeNb1−xZr/HfxSb (x = 0.125 and 0.15625) alloys for valence bands from −0.104 eV to 0.104 eV and for valence bands from −2.104 eV to −0.104 eV. From Figs 3 and 7, we find that Hf atoms obviously change the charge distribution around Fe and Nb atoms, while Zr atoms have a relatively weak effect on their charge distribution, and additionally, the doping atoms (Zr/Hf) have more obvious hybridization with Fe atoms than Nb atoms near the EF. Figure 7(a–c) show that Zr/Hf atoms have a much stronger hybridization with their nearest Fe atoms than Nb atoms from −0.104 eV to 0.104 eV, while, Fig. 7(d–f) show that the hybridizations between Zr/Hf atoms and Fe atoms become much weaker than that between Nb and Fe atoms from −2.104 eV to −0.104 eV, indicating that the strong hybridization between Zr/Hf atoms and Fe atoms only occurs in the vicinity of EF. It suggests that the increased effective hole-pockets and total DOS of X-doped FeNbSb, and decreased m* are partially derived from the stronger hybridization between X d-states and their nearest Fe d-states near the EF. Near the EF, the contribution of Hf f-states can be ignored, and Hf atoms make their nearest Fe atoms supply more states to participate in transport than Zr atoms (Fig. 8). It can well explain why Hf-doped FeNbSb has more effective hole-pockets than Zr-doped FeNbSb. Additionally, the σtot of 15.625% Hf-doped FeNbSb is higher than that of 12.5% Hf-doped FeNbSb, which is likely derived from the fact that a higher Hf content can make their nearest Fe atoms supply more d-states to hybrid with Hf d-states and to participate in transport.


Origin of high thermoelectric performance of FeNb 1 − x Zr/Hf x Sb 1 − y Sn y alloys: A first-principles study
Calculated total and partial density of states of Hf atoms for 15.625% Hf-doped FeNbSb (a) and the total nearest Fe states of X (Zr/Hf) atoms for 15.625% X-doped FeNbSb (b).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5015081&req=5

f8: Calculated total and partial density of states of Hf atoms for 15.625% Hf-doped FeNbSb (a) and the total nearest Fe states of X (Zr/Hf) atoms for 15.625% X-doped FeNbSb (b).
Mentions: In addition, to deeply study the influence of different dopants (Zr/Hf) and different doping contents, we calculated the partial charge densities of FeNb1−xZr/HfxSb (x = 0.125 and 0.15625) alloys for valence bands from −0.104 eV to 0.104 eV and for valence bands from −2.104 eV to −0.104 eV. From Figs 3 and 7, we find that Hf atoms obviously change the charge distribution around Fe and Nb atoms, while Zr atoms have a relatively weak effect on their charge distribution, and additionally, the doping atoms (Zr/Hf) have more obvious hybridization with Fe atoms than Nb atoms near the EF. Figure 7(a–c) show that Zr/Hf atoms have a much stronger hybridization with their nearest Fe atoms than Nb atoms from −0.104 eV to 0.104 eV, while, Fig. 7(d–f) show that the hybridizations between Zr/Hf atoms and Fe atoms become much weaker than that between Nb and Fe atoms from −2.104 eV to −0.104 eV, indicating that the strong hybridization between Zr/Hf atoms and Fe atoms only occurs in the vicinity of EF. It suggests that the increased effective hole-pockets and total DOS of X-doped FeNbSb, and decreased m* are partially derived from the stronger hybridization between X d-states and their nearest Fe d-states near the EF. Near the EF, the contribution of Hf f-states can be ignored, and Hf atoms make their nearest Fe atoms supply more states to participate in transport than Zr atoms (Fig. 8). It can well explain why Hf-doped FeNbSb has more effective hole-pockets than Zr-doped FeNbSb. Additionally, the σtot of 15.625% Hf-doped FeNbSb is higher than that of 12.5% Hf-doped FeNbSb, which is likely derived from the fact that a higher Hf content can make their nearest Fe atoms supply more d-states to hybrid with Hf d-states and to participate in transport.

View Article: PubMed Central - PubMed

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.

No MeSH data available.