Subtle Roles of Sb and S in Regulating the Thermoelectric Properties of N-Type PbTe to High Performance

A high ZT (thermoelectric figure of merit) of ≈1.4 at 900 K for n-type PbTe is reported, through modifying its electrical and thermal properties by incorporating Sb and S, respectively. Sb is confirmed to be an amphoteric dopant in PbTe, filling Te vacancies at low doping levels (<1%), exceeding which it enters into Pb sites. It is found that Sb-doped PbTe exhibits much higher carrier mobility than similar Bi-doped materials, and accordingly, delivers higher power factors and superior ZT. The enhanced electronic transport is attributed to the elimination of Te vacancies, which appear to strongly scatter n-type charge carriers. Building on this result, the ZT of Pb_0.9875Sb_0.0125Te is further enhanced by alloying S into the Te sublattice. The introduction of S opens the bandgap of PbTe, which suppresses bipolar conduction while simultaneously increasing the electron concentration and electrical conductivity. Furthermore, it introduces point defects and induces second phase nanostructuring, which lowers the lattice thermal conductivity to ≈0.5 W m⁻¹ K⁻¹ at 900 K, making this material a robust candidate for high-temperature (500–900 K) thermoelectric applications. It is anticipated that the insights provided here will be an important addition to the growing arsenal of strategies for optimizing the performance of thermoelectric materials.