Thermoelectric performance in a Si allotrope with ultralow thermal conductivity: a first-principles study combining phonon-limited electronic transport calculations

By structure prediction, we found a complex semiconducting Si metastable phase, named pentasilicon, which is stable at room temperature. The consists of sp2-sp3 hybrid bonds, has an ultralow thermal conductivity about 1.7 W/mK temperature, similar to those many high-performance thermoelectric materials. We the low pentasilicon originated from strong anharmonicity and crossover effect due interactions between LA mode several low-frequency quasi-local vibrations, originate bonding character. Additionally, such also leads negative expansion in pentasilicon. Furthermore, obtained energy-dependent electron relaxation lifetimes by considering electron-phonon coupling, predicted properties For example, maximum values ZT are 0.35 0.27 doping level 1019/cm3 × 1020/cm3 for p- n-type around 12 5 times silicon, respectively, 500 K. Our work provides alternative strategy improve performance Si-based