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

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. [Display omitted] •P-type SiGe thermoelectric alloys have been prepared by compositing high oxidizing CrO3 into SiGe through ball milling and SPS.•Ultrafine nano phases were obtained in SiGe matrix through in-situ regeneration strategy.•The ultralow thermal conductivity of 2.14 W m−1 K−1 at 873 K was achieved for (CrO3)0.3-Si80Ge20B0.5.•The high average ZT reaches 0.62 at 323 − 873 K for (CrO3)0.3-Si80Ge20B0.5.•The sample (CrO3)0.3-Si80Ge20B0.5 achieves the highest (ZT)eng of 0.52 which related to the conversion efficiency of 10.1% for device.