Strained Endotaxial PbS Nanoprecipitates Boosting Ultrahigh Thermoelectric Quality Factor in n‐Type PbTe As‐Cast Ingots

Abstract Lead telluride (PbTe) has long been regarded as an excellent thermoelectric material at intermediate temperature range (573–873 K); however, n‐type PbTe's performance is always relatively inferior to its p‐type counterpart mainly due to their different electronic band structures. In this work, an ultrahigh thermoelectric quality factor ( µ /κ L ≈ 1.36 × 10 5 cm 3 KJ −1 V −1 ) is reported in extra 0.3% Cu doped n‐type (PbTe) 0.9 (PbS) 0.1 as‐cast ingots. Transmission electron microscopy (TEM) characterization reveals that excess PbS exists in PbTe matrix as strained endotaxial nanoprecipitates, which affect electrical and thermal conduction discriminately: (1) coherent PbTe/PbS lattice minimizes the interface scattering of charge carriers; (2) periodic strain centers at PbTe/PbS interface exhibit intensive strain contrast, which can strongly scatter heat‐carrying phonons. Electron backscattered diffraction (EBSD) characterization illustrates very large PbTe grains (≈1 mm) in these as‐cast ingots, ensuring an extremely low grain boundary scattering rate thus a very high charge carrier mobility. Eventually, a remarkably high ZT max ≈ 1.5 at 773 K and an outstanding ZT avg ≈ 1.0 between 323 and 773 K are simultaneously achieved in the (PbTe) 0.9 (PbS) 0.1 +0.3%Cu sample; these values are highly competitive with reported state‐of‐art n‐type PbTe materials.