Band engineering and precipitation enhance thermoelectric performance of SnTe with Zn-doping

We have systematically studied the thermoelectric properties in Zn-doped SnTe. Strikingly, band convergence and embedded precipitates arising from Zn doping, can trigger a prominent improvement of thermoelectric performance. In particular, the value of dimensionless figure of merit zT has increased by 100% and up to ~0.5 at 775 K for the optimal sample with 2% Zn content. Present findings demonstrate that carrier concentration and effective mass play crucial roles on the Seebeck coefficient and power factor. The obvious deviation from the Pisarenko line (Seebeck coefficient versus carrier concentration) due to Zn-doping reveals the convergence of valence bands. When the doping concentration exceeds the solubility, precipitates occur and lead to a reduction of lattice thermal conductivity. In addition, bipolar conduction is suppressed, indicating an enlargement of band gap. The Zn-doped SnTe is shown to be a promising candidate for thermoelectric applications.