抄録
In this study, we developed a method for fabricating high-performance p-type nano-grained bulk Si-Ge thermoelectric materials by optimizing both the electronic structure with impurity elements and the reduced-grain-size with high-energy ball milling and a modified sintering process. In previous studies of p-type materials, oxidization of nano-grained sample led to unexpectedly high electrical resistivity. Besides, the high sintering temperature required for B-doping induced grain growth, consequently increased thermal conductivity. We found that co-sintering with Zr, which acts as an oxygen getter, effectively reduces the oxygen concentration in the nano-grained bulk Si-Ge samples. The sample co-sintered with Zr contained a reduced oxygen concentration of 2.1 at. %, and the electrical resistivity was also reduced to less than 3 mΩcm at 1000 K due to suppression of carrier localization. A high Seebeck coefficient and a low thermal conductivity were achieved simultaneously through constructive modifications to the electronic structure and suppressed grain growth via Ga doping, respectively. As a consequence, we achieved a record-high dimensionless figure of merit for p-type Si-Ge materials, ZT = 2.5 at 1023 K.
