Effect of in and Cd co-doping on the thermoelectric properties of Sn1-xPbxTe

Abstract

Pristine tin telluride (SnTe) with a similar electronic structure to PbTe shows inferior thermoelectric performance owing to high p-type hole concentration (1021 cm-3), high lattice thermal conductivity, κlatt (∼2.8 W mK-1 at room temperature) and large energy gap between light and heavy hole valence bands. Interestingly, 30 mol% substitution of lead in SnTe decreases the excess hole carrier concentration and lattice thermal conductivity (∼0.67 W m-1K-1 at 300 K) significantly. Here, we report the promising thermoelectric performance in Sn0.70Pb0.30Te by enhancing the Seebeck coefficient via the co-adjuvant effect of resonant level formation and valence band convergence. We obtain a Seebeck coefficient value of ∼141 μV K-1 at 300 K, which further increases to ∼260 μV K-1 at 708 K for Sn0.70Pb0.30Te - 3% Cd and 0.50% In sample. This is one of the highest S values for SnTe based system, to the best of our knowledge. In and Cd have discrete but complementary roles to augment the Seebeck coefficient value of Sn0.70Pb0.30Te where In acts as a resonant dopant and Cd serves as valence band convergent, respectively, as demonstrated by the well-known Pisarenko plot of SnTe. Finally, we have achieved a maximum thermoelectric figure of merit, zT, of ∼0.82 at 654 K for Sn0.70Pb0.30Te - 3% Cd and 0.25% In sample.