Role of Samarium as a composite in modifying the microstructure and thermoelectric properties of Bi_1.5Sb_0.5Te₃ alloy

Bi–Sb–Te-based thermoelectric (TE) materials have attracted considerable attention for solid-state cooling and low-temperature waste heat recovery owing to their excellent thermoelectric performance. In this work, the influence of samarium (Sm) incorporation on the structural, electronic, and thermoelectric properties of Bi_1.5Sb_0.5Te₃ composites synthesized via solid-state reaction followed by sintering is systematically investigated. XPS confirms the formation of Sm-rich phases at localized regions, indicating composite formation. Room-temperature Hall measurements reveal a significant enhancement in carrier mobility from 2.7 to 23 cm²V⁻¹ s⁻¹ with Sm incorporation, leading to a reduction in electrical resistivity attributed to grain-boundary passivation and defect engineering. The pristine sample exhibits the highest Seebeck coefficient due to a lower density of states and Fermi level positioning closer to the valence band, resulting in a maximum power factor of 0.26 mWm⁻¹ K⁻² at 350 K. Although Sm incorporation reduces the power factor, it substantially enhances the thermoelectric figure of merit (ZT) through a pronounced suppression of lattice thermal conductivity arising from enhanced phonon scattering at grain boundaries and secondary phase interfaces. A maximum ZT of 0.035 at 350 K is observed for the 3% Sm-doped sample, representing a 13% improvement over the pristine material. The present study provides mechanistic insights into the composite engineering of n-type Bi_1.5Sb_0.5Te₃, demonstrating the effect of rare-earth inclusion as a composite dopant in the Bi–Sb–Te alloy and its impact on thermoelectric properties.