Band convergence and nanostructure modulations lead to high thermoelectric performance in SnPb_0.04Te-y% AgSbTe₂

SnTe is a lead-free and promising mid-temperature thermoelectric material while its performance is largely hindered owing to the relatively high hole carrier concentration originating from the existence of extraordinary Sn vacancies in intrinsic SnTe. In this study, we firstly introduced excess Pb into SnTe matrix to compensate the Sn vacancies, leading to the greatly decreased carrier concentration. Then, we found that the ternary compound AgSbTe₂ plays synergistic roles in optimizing the thermoelectric transport properties of SnTe. Namely, alloying AgSbTe₂ can induce the electronic band convergence and band flattening in SnTe, leading to the significantly enhanced band effective mass (m∗) and Seebeck coefficient. Additionally, alloying AgSbTe₂ produces plentiful Ag-rich nanoprecipitates, which strengthens the scattering of phonons, leading to the lowest lattice thermal conductivity of ∼0.47 Wm⁻¹K⁻¹. By this stepwise strategy, an outstanding ZT value ∼1.1 can be attained at 823 K for the SnPb_0.04Te–12%AgSbTe₂ sample, while an average ZT can be obtained ∼ 0.72 from 400 K to 800 K for sample SnPb_0.04Te-12%AgSbTe₂. Our study further reveals the great potential for SnTe as promising thermoelectrics.