Fig. 1. A schematic illustration of the process to remove surface tin oxides (SnOx) in polycrystalline SnSe, and to reveal the intrinsic thermoelectric properties of the material.
Our facile two-step process involves the successive purification of the tin starting reagent and the synthesized SnSe samples. The use of the purified samples minimizes the presence of SnOx in the SPS-processed dense pellets. As a result, the intrinsically ultralow thermal conductivity (κtot) is finally uncovered in the purified sample (green squares on the right) in sharp contrast to the controversially high values in the untreated sample (red circles), leading to the record-high thermoelectric figure of merit, ZT, of roughly 3.1 among all bulk thermoelectric systems.