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

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(Se_0.94Br_0.06)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.