Local nanostructures enhanced the thermoelectric performance of n-type PbTe

Abstract

Microstructure control and carrier concentration engineering are effective approaches to optimize thermal transport and electrical properties in thermoelectric materials. Hereby, we have developed a facile strategy to construct locally nanostructured PbTe in a micro-sized PbTe frame (PbTe/PbTe@C:Ag) by using mixed building blocks of PbTe@C:Ag nanoparticles and PbTe nanocubes through spark plasma sintering (SPS). The carbon shell serves as a diffusion barrier to prevent grain growth leading to the formation of locally nanostructured PbTe parts with multiscale nano/micro-sized grain boundaries/interfaces, pores, Ag based nano-precipitates and other defects. They collectively scatter phonons in low-middle frequencies reducing lattice thermal conductivity significantly. In the micro-sized PbTe frame grown from pure PbTe nanocubes, temperature dependent X-ray diffraction and Hall measurements results suggest that Ag may show a dynamic doping behaviour at elevated temperature. This could further enhance the high-frequency phonon scattering and suppress the bipolar effect, resulting in a low lattice thermal conductivity of 0.39 W m⁻¹ K⁻¹. Furthermore, the micro-sized PbTe frame maintains relatively high carrier mobility. At 723 K, a high power factor of 20.4 μW cm⁻¹ K⁻² and ZT value of 1.65 have been achieved. Our strategy demonstrates superiority and versatility in constructing desired nano- and micro-structures and tuning the carrier concentration of PbTe towards high thermoelectric performance.