Defect engineering for high-performance n-Type PbSe thermoelectrics

Abstract

Introducing structural defects such as vacancies, nanoprecipitates, and dislocations is a proven means of reducing lattice thermal conductivity. However, these defects tend to be detrimental to carrier mobility. Consequently, the overall effects for enhancing ZT are often compromised. Indeed, developing strategies allowing for strong phonon scattering and high carrier mobility at the same time is a prime task in thermoelectrics. Here we present a high-performance thermoelectric system of Pb-0.95(Sb-0.033 square(0.017))Se1-yTey (square = vacancy; y = 0-0.4) embedded with unique defect architecture. Given the mean free paths of phonons and electrons, we rationally integrate multiple defects that involve point defects, vacancy-driven dense dislocations, and Te-induced nanoprecipitates with different sizes and mass fluctuations. They collectively scatter thermal phonons in a wide range of frequencies to give lattice thermal conductivity of similar to 0.4 W m(-1) K-1, which approaches to the amorphous limit. Remarkably, Te alloying increases a density of nanoprecipitates that affect mobility negligibly and impede phonons significantly, and it also decreases a density of dislocations that scatter both electrons and phonons heavily. As y is increased to 0.4, electron mobility is enhanced and lattice thermal conductivity is decreased simultaneously. As a result, Pb-0.95(Sb-0.033 square(0.017))Se0.6Te0.4 exhibits the highest ZT similar to 1.5 at 823 K, which is attributed to the markedly enhanced power factor and reduced lattice thermal conductivity, in comparison with a ZT similar to 0.9 for Pb-0.95(Sb-0.033 square(0.017))Se that contains heavy dislocations only. These results highlight the potential of defect engineering to modulate electrical and thermal transport properties independently. We also reveal the defect formation mechanisms for dislocations and nanoprecipitates embedded in Pb-0.95(Sb-0.033 square(0.017))Se0.6Te0.4 by atomic resolution spherical aberration-corrected scanning transmission electron microscopy.