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The Zintl compound Eu 2 ZnSb 2 was recently shown to have a promising thermoelectric figure of merit, zT ∼ 1 at 823 K, due to its low lattice thermal conductivity and high electronic mobility. In the current study, we show that further increases to the electronic mobility and simultaneous reductions to the lattice thermal conductivity can be achieved by isovalent alloying with Bi on the Sb site in the Eu 2 ZnSb 2−x Bi x series ( x = 0, 0.25, 1, 2). Upon alloying with Bi, the effective mass decreases and the mobility linearly increases, showing no signs of reduction due to alloy scattering. Analysis of the pair distribution functions obtained from synchrotron X-ray diffraction revealed significant local structural distortions caused by the half-occupied Zn site in this structure type. It is all the more surprising, therefore, to find that Eu 2 ZnBi 2 possesses high electronic mobility (∼100 cm 2 V −1 s −1 ) comparable to that of AM 2 X 2 Zintl compounds. The enormous degree of disorder in this series gives rise to exceptionally low lattice thermal conductivity, which is further reduced by Bi substitution due to the decreased speed of sound. Increasing the Bi content was also found to decrease the band gap while increasing the carrier concentration by two orders of magnitude. Applying a single parabolic band model suggests that Bi-rich compositions of Eu 2 ZnSb 2−x Bi x have the potential for significantly improved zT ; however, further optimization is necessary through reduction of the carrier concentration to realize high zT .
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This content will become publicly available on December 29, 2025
Defect Engineering of Bi 2 SeO 2 Thermoelectrics
Abstract Bi2SeO2is a promisingn‐type semiconductor to pair withp‐type BiCuSeO in a thermoelectric (TE) device. The TE figure of meritzTand, therefore, the device efficiency must be optimized by tuning the carrier concentration. However, electron concentrations in self‐dopedn‐type Bi2SeO2span several orders of magnitude, even in samples with the same nominal compositions. Such unsystematic variations in the electron concentration have a thermodynamic origin related to the variations in native defect concentrations. In this study, first‐principles calculations are used to show that the selenium vacancy, which is the source ofn‐type conductivity in Bi2SeO2, varies by 1–2 orders of magnitude depending on the thermodynamic conditions. It is predicted that the electron concentration can be enhanced by synthesizing under more Se‐poor conditions and/or at higher solid‐state reaction temperatures (TSSR), which promote the formation of selenium vacancies without introducing extrinsic dopants. The computational predictions are validated through solid‐state synthesis of Bi2SeO2. More than two orders of magnitude increase are observed in the electron concentration simply by adjusting the synthesis conditions. Additionally, a significant effect of grain boundary scattering on the electron mobility in Bi2SeO2is revealed, which can also be controlled by adjusting TSSR. By simultaneously optimizing the electron concentration and mobility, azTof ≈0.2 is achieved at 773 K for self‐dopedn‐type Bi2SeO2. The study highlights the need for careful control of thermodynamic growth conditions and demonstrates TE performance improvement by varying synthesis parameters according to thermodynamic guidelines.
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- Award ID(s):
- 2102409
- PAR ID:
- 10576089
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Advanced Functional Materials
- Volume:
- 35
- Issue:
- 10
- ISSN:
- 1616-301X
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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