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

SiGe alloys exhibit high thermoelectric performance in mid to high temperatures while intrinsic high thermal conductivities hinder its wide applications. Here, we report a new strategy on regeneration of ultrafine nano phases of CrSi2 and SiO2 with an average diameter of ∼130 nm by chemical reaction of Si with highly oxidizing CrO3 in p-type SiGe matrix. Based on the Debye-Callaway simulation, the nano-sized second phase leads to the reduction of phonon relaxation time, thereby reducing the thermal conductivity to ultralow value of 2.15 W m−1 K−1 at 873 K. The boundaries between the second phases (CrSi2) and the matrix (SiGe) established potential barriers, which allowed carrier filtering and phonon scattering, thus pushing up the power factor. Eventually, the sample (CrO3)0.3-Si80Ge20B0.5 reaches a peak ZT of ∼1.12 at 873 K, with an average ZT of ∼0.62 from 323 K to 873 K, achieved 55.56% improvement compared with Si80Ge20B0.5. Our method provides a promising approach for improving the thermoelectric performance of SiGe.