For years, most of the advanced polycrystalline thermoelectric (TE) materials are fabricated by spark plasma sintering (SPS) in the research field, mainly because of its high processing efficiency. However, issues like high energy consumption and an expensive apparatus have prevented the application of this strategy in industry. Herein, taking PbTe0.94Se0.06 (PTS) as a typical n-type mid-temperature material, we demonstrate that the cold sintering process (CSP) can serve as a green and cost-effective technology for preparing advanced TE materials. By selecting the solvothermal precursors as liquid sintering aids, the CSP-densified PTS shows a maximum figure of merit of 0.96 at 700 K, which is on par with, if not better than, the reported similar materials prepared by SPS. This remarkable performance is ascribed to the distinct densification procedure in the CSP: (1) the ultralow temperature alleviates the precipitation of Pb, which preserves the high carrier concentration of PTS; (2) the transient liquid phase forms intimate grain boundaries comparable to the high-temperature sintered one, leading to a high carrier mobility; (3) the dissolution-precipitation process greatly restrains the coarsening of precipitates, which effectively suppresses the bipolar effect and lattice thermal conductivity due to enhanced scattering. We believe that these results can greatly encourage the application of CSP in the future development of TE materials.
Keywords: PbTe; cold sintering process; liquid sintering aids; precipitates; thermoelectrics.