Synergetic Enhancement of the Power Factor and Suppression of Lattice Thermal Conductivity via Electronic Structure Modification and Nanostructuring on a Ni- and B-Codoped p-Type Si–Ge Alloy for Thermoelectric Application

In this study, the strategies of modifying the electronic structure, tuning carrier concentration, and nanostructuring were implemented to improve the power factor and reduce the thermal conductivity of Si–Ge simultaneously. The Si0.65–xGe0.32Ni0.03Bx (x = 0.01, 0.02, 0.03, and 0.04) nanostructure was synthesized by high-energy ball-milling. Subsequently, a high-pressure with low-temperature sintering process was carried out. A small amount of nickel (Ni) and boron (B) was introduced into Si–Ge to modify the electronic structure and optimize the carrier concentration. The sintered sample Si0.62Ge0.32Ni0.03B0.03 showed a high power factor of 2.3 mW m–1 K–2 at 1000 K, which was influenced by the modified electronic structure and optimized carrier concentration. In addition, the thermal conductivity was effectively decreased to 1.47 W m–1 K–1 due to the phonon scattering by the micro to nanoscale grain boundaries. Ultimately, a large dimensionless figure of merit ZT ∼1.56 was obtained at 1000 K. Therefore, following these strategies can improve the thermoelectric performance of earth-abundant, environmentally friendly, and nontoxic Si–Ge material.