Ultralow Lattice Thermal Conductivity and High ZT Beyond 1 Realized in BiS Nanocomposites via Bottom-Up Structure Design.

Bismuth sulfides (BiS), an n-type thermoelectric material, in expensive, and environmentally friendly. However, it has poor electrical conductivity due to its low electron concentration, and its thermoelectric properties need improvement. By adjusting the properties of microstructural units and then designing and preparing bulk materials, the transport properties are modulated to optimize thermoelectric properties. The textured structure and metal Bi dispersed in grain boundaries improved the carrier mobility, the Cl dopingimproved carrier concentration. The textured structure and metalBi dispersed in grain boundaries improved the carrier mobility, the Cl dopingimproved carrier concentration. The BiS-Cl samples reduce using NH·HO for 5 min at 673 K have a peak power factor (PF) reaching 676.6 µWmK, more than 6 times that of pristine BiS. Furthermore, the point defects, dislocations, and the micropores caused by a part of Bivolatilization contribute to the strong phonon scattering, resulting in a low lattice thermal conductivity of 0.28 WmK at 623K. Due to the synergistically optimized electrical and thermal transport properties, the values of the maximum thermoelectric figure of merit (ZT) and the average thermoelectric figure of merit (ZT) for the BiS-Cl samples reduce using NH·HO for 5 min are 1.01 at ≈673 K and 0.63 (323-673 K), respectively. This study demonstrates that bottom-up structure design can effectively strategize the improvement of thermoelectric performance.