Enhanced thermoelectric performance and observation of WAL effect in Se-substituted BiSbTe3 single crystals

Bi–Sb–Te-based materials are benchmark thermoelectrics for room temperature applications owing to their optimal electronic band structure that yields a large value of thermopower (S ∼ 300 μV/K), ultralow thermal conductivity (∼1 W/mK), combined with a convenient synthesis procedure. To further improve the thermoelectric performance of these materials, new strategies are required without compromising their intrinsic electronic properties. The isoelectronic substitution can be a rational approach, as it is primarily employed to reduce the lattice thermal conductivity with minimal alteration of the electronic structure of the material system. Therefore, in the present work, we investigated the effect of Se substitution in BiSbTe3 single crystals grown by the modified Bridgman method. X-ray diffraction studies confirm that the crystal structure of the material is maintained with Se substitution. Contrary to the simple expectation, we observe a dramatic non-monotonic evolution in its electronic transport behavior, in particular, the optimized composition BiSbTe2.5Se0.5 exhibits a sevenfold enhancement in its thermoelectric power factor compared to the pristine BiSbTe3, which can be attributed to a massive reduction in its electrical resistivity. Upon further increasing Se substitution drives a metal-to-semiconductor transition in BiSbTe1.5Se1.5, displaying a negative magnetoresistance and weak antilocalization signatures. Density functional theory calculations performed using Vienna ab initio simulation package reveal that isoelectronic substitution induces significant modifications in the electronic structure of Bi–Sb–Te-based alloys, which is in accordance with the experimentally observed transport properties. Our findings therefore demonstrate that controlled isoelectronic substitution can effectively tune the electronic properties of Bi–Sb–Te-based alloys and thereby provide a reliable route for thermoelectric performance optimization.