Intrinsically Low Thermal Conductivity in BiSbSe3: A Promising Thermoelectric Material with Multiple Conduction Bands

Abstract

Bi2Se3, as a Te-free alternative of room-temperature state-of-the-art thermoelectric (TE) Bi2Te3, has attracted little attention due to its poor electrical transport properties and high thermal conductivity. Interestingly, BiSbSe3, a product of alloying 50% Sb on Bi sites, shows outstanding electron and phonon transports. BiSbSe3 possesses orthorhombic structure and exhibits multiple conduction bands, which can be activated when the carrier density is increased as high as ≈3.7 × 1020 cm−3 through heavily Br doping, resulting in simultaneously enhancing the electrical conductivities and Seebeck coefficients. Meanwhile, an extremely low thermal conductivity (≈0.6–0.4 W m−1 K−1 at 300–800 K) is found in BiSbSe3. Both first-principles calculations and elastic properties measurements show the strong anharmonicity and support the ultra-low thermal conductivity of BiSbSe3. Finally, a maximum dimensionless figure of merit ZT ∼ 1.4 at 800 K is achieved in BiSb(Se0.94Br0.06)3, which is comparable to the most n-type Te-free TE materials. The present results indicate that BiSbSe3 is a new and a robust candidate for TE power generation in medium-temperature range.