Strained Endotaxial PbS Nanoprecipitates Boosting Ultrahigh Thermoelectric Quality Factor in n-Type PbTe As-Cast...

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 × 10⁵ cm³ 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.