Dislocations Stabilized by Point Defects Increase Brittleness in PbTe

Advanced Functional Materials, vol. 31

Abstract

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.

Authors 8

1. James Patrick Male

   Northwestern University

   Affiliation as printed

   Department of Materials Science and Engineering Northwestern University Evanston IL USA

   Department of Materials Science and Engineering, Northwestern University, Evanston, IL, USA

2. Lamya Abdellaoui

   Max-Planck-Institut für Nachhaltige Materialien

   Affiliation as printed

   Max‐Planck‐Institut für Eisenforschung GmbH 40237 Düsseldorf Germany

3. Yuan Yu Aachen Institute of Physics IA

   RWTH Aachen University

   Affiliation as printed

   Institute of Physics IA RWTH Aachen University 52056 Aachen Germany

   Institute of Physics IA, RWTH Aachen University, 52056 Aachen, Germany

4. Siyuan Zhang

   Max-Planck-Institut für Nachhaltige Materialien

   Affiliation as printed

   Max‐Planck‐Institut für Eisenforschung GmbH 40237 Düsseldorf Germany

5. Naomi A. Pieczulewski

   Northwestern University

   Affiliation as printed

   Department of Materials Science and Engineering Northwestern University Evanston IL USA

   Department of Materials Science and Engineering, Northwestern University, Evanston, IL, USA

6. Oana Cojocaru‐Mirédin Aachen Institute of Physics IA

   RWTH Aachen University

   Affiliation as printed

   Institute of Physics IA RWTH Aachen University 52056 Aachen Germany

   Institute of Physics IA, RWTH Aachen University, 52056 Aachen, Germany

7. Christina Scheu

   Max-Planck-Institut für Nachhaltige Materialien

   Affiliation as printed

   Max‐Planck‐Institut für Eisenforschung GmbH 40237 Düsseldorf Germany

8. Gerald Jeffrey Snyder corresponding

   Northwestern University

   Affiliation as printed

   Department of Materials Science and Engineering Northwestern University Evanston IL USA

   Department of Materials Science and Engineering, Northwestern University, Evanston, IL, USA