Dislocations Stabilized by Point Defects Increase Brittleness in PbTe

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.

Theoretical insights into the Peierls plasticity in SrTiO3 ceramics via dislocation remodelling

“…The method in this paper also handles the interaction between dislocations and vacancies, which the traditional GSF approach fails to deal with. It is widely believed that point defect usually shows a pinning effect on dislocation and accordingly, reduces the dislocation mobility [36][37][38][39][40][41] . However, the calculation based on our model indicates that oxygen vacancies in SrTiO 3 can reduce the average misfit energy and the Peierls stress, contributing to the nucleation and activation of 〈110〉{110} edge dislocation.…”

Mapping Thermoelectric Transport in a Multicomponent Alloy Space

“…Dislocation-phonon interactions have been shown to explain the high thermoelectric performance in numerous materials, as the lattice strain produced from high dislocation densities will lead to strong lattice softening and phonon scattering effects. [44][45][46][47] Alloying elements can immobilize dislocations, preventing dislocation glide and annihilation, in order to maintain higher dislocation densities, however this is shown to be accompanied by embrittlement. [45,[48][49][50][51] Since the perturbation to elastic constants in addition to the elastic strain around the defect is primarily responsible for this dislocation pinning, point defects with a high Γ R parameter would be most effective for this strategy.…”

“…[44][45][46][47] Alloying elements can immobilize dislocations, preventing dislocation glide and annihilation, in order to maintain higher dislocation densities, however this is shown to be accompanied by embrittlement. [45,[48][49][50][51] Since the perturbation to elastic constants in addition to the elastic strain around the defect is primarily responsible for this dislocation pinning, point defects with a high Γ R parameter would be most effective for this strategy. In the case of PbTe, co-doping with Na and Eu appears to best maintain a high dislocation density even when dislocations become more mobile at elevated temperatures, performing better than samples with just a single dopant.…”

Development of Solar Energy Systems Based on High Performance Bulk and Film Thermoelectric Modules

“…On the other hand, this TE material has satisfactory mechanical characteristics, in contrast with high-efficiency p-type PbTe [45][46][47][48]. This property is very important for application in thermoelectric energy modules [49][50][51].…”