Abstract
Defect chemistry is critical to designing high performance thermoelectric materials. In SnTe, the naturally large density of cation vacancies results in excessive hole doping and frustrates the ability to control the thermoelectric properties. Yet, recent work also associates the vacancies with suppressed sound velocities and low lattice thermal conductivity, underscoring the need to understand the interplay between alloying, vacancies, and the transport properties of SnTe. Here, we report solid solutions of SnTe with NaSbTe2 and NaBiTe2 (NaSnmSbTem+2 and NaSnmBiTem+2, respectively) and focus on the impact of the ternary alloys on the cation vacancies and thermoelectric properties. We find introduction of NaSbTe2, but not NaBiTe2, into SnTe nearly doubles the natural concentration of Sn vacancies. Furthermore, DFT calculations suggest that both NaSbTe2 and NaBiTe2 facilitate valence band convergence and simultaneously narrow the band gap. These effects improve the power factors but also make the alloys more prone to detrimental bipolar diffusion. Indeed, the performance of NaSnmBiTem+2 is limited by strong bipolar transport and only exhibits modest maximum ZTs ≈ 0.85 at 900 K. In NaSnmSbTem+2 however, the doubled vacancy concentration raises the charge carrier density and suppresses bipolar diffusion, resulting in superior power factors than those of the Bi-containing analogues. Lastly, NaSbTe2 incorporation lowers the sound velocity of SnTe to give glasslike lattice thermal conductivities. Facilitated by the favorable impacts of band convergence, vacancy-augmented hole concentration, and lattice softening, NaSnmSbTem+2 reaches high ZT ≈ 1.2 at 800-900 K and a competitive average ZTavg of 0.7 over 300-873 K. The difference in ZT between two chemically similar compounds underscores the importance of intrinsic defects in engineering high-performance thermoelectrics.
| Original language | English (US) |
|---|---|
| Pages (from-to) | 12524-12535 |
| Number of pages | 12 |
| Journal | Journal of the American Chemical Society |
| Volume | 142 |
| Issue number | 28 |
| DOIs | |
| State | Published - Jul 15 2020 |
Funding
This work is primarily supported by the U.S Department of Energy, Office of Science and Office of Basic Energy Sciences under award number DE-SC0014520. This work made use of the EPIC facility of Northwestern University’s NU ANCE Center, which has received support from the Soft and Hybrid Nanotechnology Experimental (SHyNE) Resource (NSF ECCS-1542205); the MRSEC program (NSF DMR-1720139) at the Materials Research Center; the International Institute for Nanotechnology (IIN); the Keck Foundation; and the State of Illinois, through the IIN. This work also made use of the MatCI Facility which receives support from the MRSEC Program (NSF DMR-1720139) of the Materials Research Center at Northwestern University. This material is based upon work supported by the National Science Foundation Graduate Research Fellowship under Grant No. DGE-1324585. G.J.S. and J.M. acknowledge the support of award 70NANB19H005 from the U.S. Department of Commerce, National Institute of Standards and Technology as part of the Center for Hierarchical Materials Design (CHiMaD). The work in the Materials Science Division of Argonne National Laboratory (low-temperature heat capacity measurements) was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division, under contract No. DE-AC02-06CH11357.
ASJC Scopus subject areas
- Catalysis
- General Chemistry
- Biochemistry
- Colloid and Surface Chemistry