Manipulating the Combustion Wave during Self-Propagating Synthesis for High Thermoelectric Performance of Layered Oxychalcogenide Bi_1-xPb_xCuSeO

Novel time- and energy-efficient synthesis methods, especially those adaptable to large-scale industrial processing, are of vital importance for broader applications of thermoelectrics. We herein reported a case study of layer-structured oxychalcogenides Bi_1-xPb_xCuSeO (x = 0-10%) with emphases on the reaction mechanism of self-propagating high-temperature synthesis (SHS) and the impact of SHS conditions on the thermoelectric properties. The combined results of X-ray powder diffraction, differential scanning calorimetry, and quenching experiments corroborated that the SHS process of BiCuSeO consisted two fast binary SHS reactions (2 Bi+3 Se → Bi₂Se₃ and 2 Cu+Se → Cu₂Se) intimately coupled with two relatively slow solid-state diffusion reactions (2 Bi₂Se₃+B₂O₃ → 3 Bi₂SeO₂ and then Bi₂SeO₂+Cu₂Se → 2 BiCuSeO). The formation rate of the reaction intermediate Bi₂SeO₂ was the bottleneck in the SHS process of BiCuSeO. Importantly, we found that adding PbO in the starting materials has (i) facilitated the formation of Bi₂SeO₂ and thus significantly reduced the SHS reaction time; (ii) improved the phase purity and sample homogeneity; (iii) increased the power factor via increasing both carrier concentration and effective mass; and (iv) reduced the lattice thermal conductivity via more point defect phonon scattering. As a result, a state-of-the-art ZT value ∼1.2 has been attained at 923 K for Bi_0.94Pb_0.06CuSeO. These results not only open a new avenue for mass production of single phased multinary thermoelectric materials but also inspire more investigation into the SHS mechanisms of multinary materials in diverse fields of material science and engineering.