Manipulating the Combustion Wave during Self-Propagating Synthesis for High Thermoelectric Performance of Layered Oxychalcogenide Bi1-xPbxCuSeO

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 Bi1-xPbxCuSeO (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 2Cu+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 similar to 1.2 has been attained at 923 K for Bi0.94Pb0.06CuSeO. 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.