Broadening temperature plateau of high zTs in PbTe doped Bi0·3Sb1·7Te3 through defect carrier regulation and multi-scale phonon scattering

Abstract

(Bi, Sb)2Te3 alloys are a promising class of thermoelectrics family for ambient temperature application, which has been widely concerned by the community. However, due to the narrow bandgap, the bipolar excitation limits thermoelectric figure of merit (zT) improvement as temperature rises. We herein combinate extrinsic impurities with intrinsic point defects to regulate carrier concentration and enable multi-scale phonon scattering simultaneously. Multiple types of defects interaction are triggered by PbTe doping to tune the carrier concentration, as well as the band gap is further expanded to suppresses the bipolar excitation at high temperatures. This result leads to the overall enhancement of electrical transport properties. With PbTe addition, the homologous multi-scale defects (including point defects, Te nanoprecipitates and high-density grain boundaries) are produced to strengthen phonon scatterings effectively in BST matrix, resulting a declined in lattice thermal conductivity. Finally, a high zT of ∼1.25 at 425 K and a superior average zT (zTavg) of ∼1.21 (350–500 K) are obtained in BST samples, projecting a maximum conversion efficiency (ηmax) of ∼7.8% at ΔT = 200 K. Importantly, this enhancement of high ranged zTs achieved by rational defect design in BST provides a new insight for promoting high-efficiency thermoelectrics to real applications.