Abstract
Dislocations and the residual strain they produce are instrumental for the high thermoelectric figure of merit, zT ≈ 2, in lead chalcogenides. However, these materials tend to be brittle, barring them from practical green energy and deep space applications. Nonetheless, the bulk of thermoelectrics research focuses on increasing zT without considering mechanical performance. Optimized thermoelectric materials always involve high point defect concentrations for doping and solid solution alloying. Brittle materials show limited plasticity (dislocation motion), yet clear links between crystallographic defects and embrittlement are hitherto unestablished in PbTe. This study identifies connections between dislocations, point defects, and the brittleness (correlated with Vickers hardness) in single crystal and polycrystalline PbTe with various n- and p-type dopants. Speed of sound measurements show a lack of electronic bond stiffening in p-type PbTe, contrary to the previous speculation. Instead, varied routes of point defect–dislocation interaction restrict dislocation motion and drive embrittlement: dopants with low doping efficiency cause high defect concentrations, interstitial n-type dopants (Ag and Cu) create highly strained obstacles to dislocation motion, and highly mobile dopants can distribute inhomogeneously or segregate to dislocations. These results illustrate the consequences of excessive defect engineering and the necessity to consider both mechanical and thermoelectric performance when researching thermoelectric materials for practical applications.
Original language | English (US) |
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Article number | 2108006 |
Journal | Advanced Functional Materials |
Volume | 31 |
Issue number | 52 |
DOIs | |
State | Published - Dec 22 2021 |
Funding
This work made use of the MatCI Facility supported by the MRSEC program of the National Science Foundation (DMR‐1720139) at the Materials Research Center of Northwestern University. Work by J.P.M. was supported by a National Aeronautics and Space Administration (NASA) Space Technology Graduate Research Opportunity. J.P.M., N.P., and G.J.S. thank 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). L.A., S.Z., and S.S. acknowledge Dr. Stefan Zaefferer for fruitful discussions. Y.Y. and O.C.‐M. acknowledge the financial support of DFG (German Science Foundation) within the project SFB 917 nanoswitches.
Keywords
- brittleness
- doping
- hardness
- mechanical stability
- thermoelectrics
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- General Chemistry
- Biomaterials
- General Materials Science
- Condensed Matter Physics
- Electrochemistry