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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

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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.


The calculated band structures of Zr, Hf mono-doped and Hf/Sn co-doped FeNbSb systems using 2 × 2 × 2 (a–c,g) and 1 × 1 × 5 (d–f,h) FeNbSb supercell. The valence band valleys (hole-pockets) at the vicinity of the EF play a major role on their transport properties.
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f5: The calculated band structures of Zr, Hf mono-doped and Hf/Sn co-doped FeNbSb systems using 2 × 2 × 2 (a–c,g) and 1 × 1 × 5 (d–f,h) FeNbSb supercell. The valence band valleys (hole-pockets) at the vicinity of the EF play a major role on their transport properties.

Mentions: The electronic structures of FeNb1−xZr/HfxSb alloys were calculated to analyze their different transport coefficients using the first-principles method (Figs 5 and 6). It is known that multiple band valleys (multiple carrier-pockets) and large valley degeneracy are beneficial to achieve high ZT373839. Band degeneracy increases when multiple bands have the same or comparable energy within kBT, which can contribute to increasing the Seebeck coefficient (Stot). If the number of the valence band valleys (or conduction band valleys) near the Fermi level (EF) is m in the FeNb1−xZr/HfxSb systems, the total electrical conductivity (σtot) and Seebeck coefficient (Stot) can be expressed as:


Origin of high thermoelectric performance of FeNb 1 − x Zr/Hf x Sb 1 − y Sn y alloys: A first-principles study
The calculated band structures of Zr, Hf mono-doped and Hf/Sn co-doped FeNbSb systems using 2 × 2 × 2 (a–c,g) and 1 × 1 × 5 (d–f,h) FeNbSb supercell. The valence band valleys (hole-pockets) at the vicinity of the EF play a major role on their transport properties.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f5: The calculated band structures of Zr, Hf mono-doped and Hf/Sn co-doped FeNbSb systems using 2 × 2 × 2 (a–c,g) and 1 × 1 × 5 (d–f,h) FeNbSb supercell. The valence band valleys (hole-pockets) at the vicinity of the EF play a major role on their transport properties.
Mentions: The electronic structures of FeNb1−xZr/HfxSb alloys were calculated to analyze their different transport coefficients using the first-principles method (Figs 5 and 6). It is known that multiple band valleys (multiple carrier-pockets) and large valley degeneracy are beneficial to achieve high ZT373839. Band degeneracy increases when multiple bands have the same or comparable energy within kBT, which can contribute to increasing the Seebeck coefficient (Stot). If the number of the valence band valleys (or conduction band valleys) near the Fermi level (EF) is m in the FeNb1−xZr/HfxSb systems, the total electrical conductivity (σtot) and Seebeck coefficient (Stot) can be expressed as:

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.