Here we report that CdTe alloying and Sb doping increase the density-of-states effective mass and introduce endotaxial nanostructuring in n-type PbTe, resulting in enhanced thermoelectric performance. A prior theoretical prediction for the presence of resonance states in the conduction band of this system, however, could not be confirmed. An amount of 3 mol % CdTe alloying widens the band gap of PbTe by 50%, leading to enhanced carrier effective mass and Seebeck coefficient. This effect is even more pronounced at high temperatures where the solubility of CdTe increases. At 800 K, when the carrier concentration is the same (4 × 1019 cm-3), the Seebeck coefficient of CdTe-alloyed PbTe is -195 μV K-1, 16% higher than that of the Cd-free control sample (-168 μV K-1). Sb doping considerably increases the electron concentration of Pb0.97Cd0.03Te, giving rise to optimized power factors of ∼17 μW cm-1 K-2 at 800 K. More importantly, Sb induces strained endotaxial nanostructures evenly distributed in the matrix. These Sb-rich nanostructures account for the ∼40% reduction in the lattice thermal conductivity over the whole measured temperature range. As a result, a maximum ZT of 1.2 is attained at 750 K in 0.5 mol % Sb-doped Pb0.97Cd0.03Te alloys.
Keywords: electronic structure; lead telluride; nanostructuring; thermal conductivity; thermoelectric.