Phonon relaxation effect by regeneration of nano-inclusions in SiGe for ultralow thermal conductivity and enhanced thermoelectric performance

Abstract

SiGe alloys exhibit high thermoelectric performance at mid to high temperatures, but their wide applications are hindered by intrinsically high thermal conductivity. Here, we report a new strategy for regenerating ultrafine nano phases of CrSi2 and SiO2 with an average grain size of approximate 130 nm by chemical reaction of Si and strong oxidizing CrO3 in a p-type SiGe matrix. Based on the Debye-Callaway calculation, the nano-sized second phase leads to a reduction in phonon relaxation time, thereby lowering the thermal conductivity to an ultralow value of 2.15 W m−1 K−1 at 873 K. The boundaries between the second phases (CrSi2) and the matrix (SiGe) establish potential barriers, allowing carrier filtering and phonon scattering, thus increasing the power factor. Eventually, the sample (CrO3)0.3-Si80Ge20B0.5 reaches a peak ZT of approximately 1.12 at 873 K, with an average ZT of approximately 0.62 from 323 K to 873 K, representing a 55.56% improvement compared with Si80Ge20B0.5. Our method provides a promising approach for enhancing the thermoelectric performance of SiGe.