Band Convergence and Phonon Scattering Mediated Improved Thermoelectric Performance of SnTe–PbTe Nanocomposites

SnTe exhibits poor thermoelectric figure of merit owing to Sn vacancies that give rise to a low p-type Seebeck coefficient and high electrical–thermal conductivities. Here, we reported thermoelectric properties of a composite material synthesized by vacuum hot pressing a mixture of preformed p-type SnTe and n-type PbTe. Detailed characterization revealed that the composite material has SnTe alloyed with PbTe along with n-PbTe nanoinclusions. The cumulative effect of alloying-induced valence band convergence along with energy filtering of charge carriers at the SnTe–PbTe (p–n) interface resulted in an enhanced Seebeck coefficient in the composite material. A significant lowering of thermal conductivity was achieved by phonon scattering at coherent nano p–n junctions and substitution point defects due to alloying. The high Seebeck coefficient along with depressed thermal conductivity in the composite (SnTe)0.5(PbTe)0.5 resulted in the highest figure of merit (ZT) of ∼1.2 at 750 K (i.e., 724% higher compared to pure SnTe) and average ZT of ∼0.5 in a temperature range of 300–750 K. A single-leg thermoelectric power generator fabricated using optimized (SnTe)0.5(PbTe)0.5 showed a conversion efficiency of ∼4.9% for a temperature difference of 400 K.