Dynamic doping and Cottrell atmosphere optimize the thermoelectric performance of n-type PbTe

TL;DR

This study enhances n-type PbTe thermoelectric performance by combining dynamic doping with Cottrell atmospheres, achieving an average zT of 1.0 over 400-825 K through defect engineering and temperature-dependent dopant behavior.

Contribution

It introduces a novel approach of using dynamic doping and dislocation interactions to optimize thermoelectric properties of PbTe across a broad temperature range.

Findings

Achieved an average zT of 1.0 between 400 and 825 K.

Demonstrated in situ dissolution of Ag2Te precipitates at high temperatures.

Showed that Ag atoms form Cottrell atmospheres along dislocations, reducing thermal conductivity.

Abstract

High thermoelectric energy conversion efficiency requires a large figure-of-merit, zT, over a broad temperature range. To achieve this, we optimize the carrier concentrations of n-type PbTe from room up to hot-end temperatures by co-doping Bi and Ag. Bi is an efficient n-type dopant in PbTe, often leading to excessive carrier concentration at room temperature. As revealed by density functional theory calculations, the formation of Bi and Ag defect complexes is exploited to optimize the room temperature carrier concentration. At elevated temperatures, we demonstrate the dynamic dissolution of Ag2Te precipitates in PbTe in situ by heating in a scanning transmission electron microscope. The release of n-type Ag interstitials with increasing temperature fulfills the requirement of higher carrier concentrations at the hot end. Moreover, as characterized by atom probe tomography, Ag atoms aggregate along parallel dislocation arrays to form Cottrell atmospheres. This results in enhanced phonon scattering and leads to a low lattice thermal conductivity. As a result of the synergy of dynamic doping and phonon scattering at decorated dislocations, an average zT of 1.0 is achieved in n-type Bi/Ag-codoped PbTe between 400 and 825 K. Introducing dopants with temperature-dependent solubility and strong interaction with dislocation cores enables simultaneous optimization of the average power factor and thermal conductivity, providing a new concept to exploit in the field of thermoelectrics.