Broad temperature plateau for thermoelectric figure of merit ZT>2 in phase-separated PbTe_0.7S_0.3

摘要

Thermoelectrics interconvert heat to electricity and are of great interest in waste heat recovery, solid-state cooling and so on. The efficiency of thermoelectric materials depends directly on the average ZT (dimensionless figure of merit) over a certain temperature range, which historically has been challenging to increase. Here we report that 2.5% K-doped PbTe_0.7S_0.3 achieves a ZT of >2 for a very wide temperature range from 673 to 923?K and has a record high average ZT of 1.56 (corresponding to a theoretical energy conversion efficiency of ~20.7% at the temperature gradient from 300 to 900?K). The PbTe_0.7S_0.3 composition shows spinodal decomposition with large PbTe -rich and PbS -rich regions where each region exhibits dissimilar types of nanostructures. Such high average ZT is obtained by synergistically optimized electrical- and thermal-transport properties via carrier concentration tuning, band structure engineering and hierarchical architecturing, and highlights a realistic prospect of wide applications of thermoelectrics.