Computations have predicted good thermoelectric performance for a number of Zintl phases when doped n-type. Combined with the successful experimental realization of n-type KGaSb 4 , KAlSb 4 , and Mg 3 Sb 2 with zT ≳ 1, this has fueled efforts to discover novel n-type dopable Zintl phases. However, a majority of Zintl phases exhibit strong proclivity toward p-type doping and prior successes in finding n-type dopable Zintls were largely serendipitous. Herein we use modern first-principles defect calculations to study trends in the dopability of Zintl pnictides and find that the average oxidation state of the anion is a useful chemical guide to identify novel n-type dopable phases. Specifically, we observe that Zintl pnictides with average oxidation of the anion near −1 are n-type dopable. The trend is mainly a consequence of the high formation energy of native acceptor defects ( e.g. cation vacancies) and the resulting absence of charge (electron) compensation. Using the oxidation state guide in conjunction with a descriptor of thermoelectric performance, we conduct a large-scale materials search and identify promising candidates that are n-type dopable.
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Potential for high thermoelectric performance in n-type Zintl compounds: a case study of Ba doped KAlSb 4
High-throughput calculations (first-principles density functional theory and semi-empirical transport models) have the potential to guide the discovery of new thermoelectric materials. Herein we have computationally assessed the potential for thermoelectric performance of 145 complex Zintl pnictides. Of the 145 Zintl compounds assessed, 17% show promising n-type transport properties, compared with only 6% showing promising p-type transport. We predict that n-type Zintl compounds should exhibit high mobility μ n while maintaining the low thermal conductivity κ L typical of Zintl phases. Thus, not only do candidate n-type Zintls outnumber their p-type counterparts, but they may also exhibit improved thermoelectric performance. From the computational search, we have selected n-type KAlSb 4 as a promising thermoelectric material. Synthesis and characterization of polycrystalline KAlSb 4 reveals non-degenerate n-type transport. With Ba substitution, the carrier concentration is tuned between 10 18 and 10 19 e − cm −3 with a maximum Ba solubility of 0.7% on the K site. High temperature transport measurements confirm a high μ n (50 cm 2 V −1 s −1 ) coupled with a near minimum κ L (0.5 W m −1 K −1 ) at 370 °C. Together, these properties yield a zT of 0.7 at 370 °C for the composition K 0.99 Ba 0.01 AlSb 4 . Based on the theoretical predictions and subsequent experimental validation, we find significant motivation for the exploration of n-type thermoelectric performance in other Zintl pnictides.
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- PAR ID:
- 10079414
- Date Published:
- Journal Name:
- Journal of Materials Chemistry A
- Volume:
- 5
- Issue:
- 8
- ISSN:
- 2050-7488
- Page Range / eLocation ID:
- 4036 to 4046
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/c6ta09532a
