Title: Contrasting SnTe–NaSbTe₂ and SnTe–NaBiTe₂ Thermoelectric Alloys: High Performance Facilitated by Increased Cation Vacancies and Lattice Softening

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,more » 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.« less

Authors:

Slade, Tyler J. ^[1]; Pal, Koushik ^[1]; Grovogui, Jann A. ^[1]; Bailey, Trevor P. ^[2]; Male, James ^[1]; Khoury, Jason F. ^[1]; Zhou, Xiuquan ^[3]; Chung, Duck Young ^[3]; Snyder, G. Jeffery ^[1]; Uher, Ctirad ^[2]; Dravid, Vinayak P. ^[1]; Wolverton, Chris ^[1]; Kanatzidis, Mercouri G. ^[4]

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+ Show Author Affiliations

1. Northwestern Univ., Evanston, IL (United States)
2. Univ. of Michigan, Ann Arbor, MI (United States)
3. Argonne National Lab. (ANL), Lemont, IL (United States)
4. Northwestern Univ., Evanston, IL (United States); Argonne National Lab. (ANL), Lemont, IL (United States)

Publication Date:

Mon Jul 06 00:00:00 EDT 2020

Research Org.:

Argonne National Laboratory (ANL), Argonne, IL (United States); Northwestern Univ., Evanston, IL (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Office of Basic Energy Sciences (BES); National Science Foundation (NSF); US Dept. of Commerce; National Institute of Standards and Technology (NIST), Center for Hierarchical Materials Design (CHiMaD); USDOE Office of Science (SC), Basic Energy Sciences (BES)

OSTI Identifier:

1657192

Alternate Identifier(s):

OSTI ID: 1778879

Grant/Contract Number:  

AC02-06CH11357; SC0014520; DMR-1720139; DGE-1324585; 70NANB19H005

Resource Type:

Accepted Manuscript

Journal Name:

Journal of the American Chemical Society

Additional Journal Information:

Journal Volume: 142; Journal Issue: 28; Journal ID: ISSN 0002-7863

Publisher:

American Chemical Society (ACS)

Country of Publication:

United States

Language:

English

Subject:

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; Thermal conductivity; alloys; lattices; defects in solids; electrical conductivity