Intrinsically Low Thermal Conductivity and High Carrier Mobility in Dual Topological Quantum Material, n-Type BiTe.

A challenge in thermoelectrics is to achieve intrinsically low thermal conductivity in crystalline solids while maintaining a high carrier mobility (μ). Topological quantum materials, such as the topological insulator (TI) or topological crystalline insulator (TCI) can exhibit high μ. Weak topological insulators (WTI) are of interest because of their layered hetero-structural nature which has a low lattice thermal conductivity (κlat ). BiTe, a unique member of the (Bi2 )m (Bi2 Te3 )n homologous series (m:n=1:2), has both the quantum states, TCI and WTI, which is distinct from the conventional strong TI, Bi2 Te3 (where m:n=0:1). Herein, we report intrinsically low κlat of 0.47-0.8 W m-1  K-1 in the 300-650 K range in BiTe resulting from low energy optical phonon branches which originate primarily from the localized vibrations of Bi bilayer. It has high μ≈516 cm2  V-1  s-1 and 707 cm2  V-1  s-1 along parallel and perpendicular to the spark plasma sintering (SPS) directions, respectively, at room temperature.