Enhancement of thermoelectric performance in n-type Si90Ge10-based alloy by metallic Zn doping

Abstract

Silicon–germanium (SiGe) alloy has become one of the representative high-temperature thermoelectric (TE) materials due to its advantages of stability, non-toxicity, oxidation resistance, and high mechanical strength. However, the high thermal conductivity and expensive Ge greatly limit the enhancement of zT value and its application. In this paper, n-type Si90Ge10P2Znx nanocomposites were prepared by ball milling and spark plasma sintering. By adjusting the Zn content and sintering time, multiple phonon-scattering centers, such as Zn precipitates, nano-pores, and layered structures, have been introduced into the SiGe matrix. The thermal conductivity was significantly reduced to 2.59 W m−1 K−1 without deteriorate power factor (PF), thus leading to a high zT value of 1.23 at 873 K. At 323–873 K, the average zT value (zTavg) also reached 0.6, increased by approximately 25% in comparison to the reported value using the same ratio of Si90Ge10. Compared with the conventional radioisotope TE generator with Si80Ge20 composition, the zTavg value increased by nearly 30% with only half of Ge, giving strong impetus to the application of SiGe-based TE materials.