The ultralow thermal conductivity and ultrahigh thermoelectric performance of fluorinated Sn2Bi sheet in room temperature.

It has been a grand challenge to develop efficient thermoelectric materials for room temperature applications. Here, motivated by the recent experimental synthesis of Sn 2 Bi sheet on silicon wafer [ Phys. Rev. Lett. 121, 126801 (2018)], for the first time we find that fluorination not only can stabilize Sn 2 Bi sheet in free-standing condition but also can significantly enhance the thermoelectric performance. The fluorinated Sn 2 Bi sheet exhibits an enlarged three-phonon scattering phase space, reduced group velocity and enhanced anharmonicity, leading to an ultralow lattice thermal conductivity of 0.19 W m⁻¹ K⁻¹ and an ultrahigh ZT value of 2.45 (1.70) at 300 K for n- (p-) doping, which are much higher than the reported values for n -type Bi 2 Te 2.79 Se 0.21 polycrystalline alloy (ZT~1.2 at 357 K), and p -type nanocomposites Bi 0.48 Sb 1.52 Te 3 (ZT~1.4 at 475 K), thus the fluorinated Sn 2 Bi sheet can be a promising candidate for room-temperature thermoelectric applications. Image 1 Based on Sn 2 Bi sheet synthesized recently, for the first time we show that fluorination can significantly improve the thermoelectric performance in room temperature with the following features: • A high TE power factor of 4596 μW m − 1 K − 2 . • An ultralow lattice thermal conductivity of 0.19 W m⁻¹ K⁻¹. • An ultrahigh ZT of 2.45 (1.70) for n- (p-) doped sheet. [ABSTRACT FROM AUTHOR]