Intrinsically Low Thermal Conductivity in BiSbSe 3 : A Promising Thermoelectric Material with Multiple Conduction Bands

Bi 2 Se 3 , as a Te‐free alternative of room‐temperature state‐of‐the‐art thermoelectric (TE) Bi 2 Te 3 , has attracted little attention due to its poor electrical transport properties and high thermal conductivity. Interestingly, BiSbSe 3 , a product of alloying 50% Sb on Bi sites, shows outstanding electron and phonon transports. BiSbSe 3 possesses orthorhombic structure and exhibits multiple conduction bands, which can be activated when the carrier density is increased as high as ≈3.7 × 10 20 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 BiSbSe 3 . Both first‐principles calculations and elastic properties measurements show the strong anharmonicity and support the ultra‐low thermal conductivity of BiSbSe 3 . Finally, a maximum dimensionless figure of merit ZT ∼ 1.4 at 800 K is achieved in BiSb(Se 0.94 Br 0.06 ) 3 , which is comparable to the most n ‐type Te‐free TE materials. The present results indicate that BiSbSe 3 is a new and a robust candidate for TE power generation in medium‐temperature range.