Enhancing thermoelectric performance of p-type BixSb2−xTe3 by optimizing carrier concentration

Bismuth telluride-based alloys are widely used as commercial thermoelectric materials around room temperature. In this study, Bi_0.46Sb_1.54Te₃ alloys were synthesized using a solid-state reaction method with precise control of the Bi/Sb stoichiometric ratio. Increasing Bi content enhanced the bond polarity, raising the formation energy of antisite defects, and reducing carrier concentration. The carrier concentration decreased from $5.7\times 10^{19}$ cm⁻³ to $4.2\times 10^{19}$ cm⁻³. Additionally, SEM observations identified a significant presence of precipitates, while TEM analysis revealed nano-sized secondary phases within the matrix. Due to the scattering of phonons by precipitates on the grain surfaces and nano-sized secondary phases, the lattice thermal conductivity near room temperature was significantly reduced to 0.29 W/m K. The optimized composition achieved a peak ZT of 1.59 at 350 K and an average ZT (ZT${}_{\text{ave}}$) of 1.46 between 300–500 K. This work demonstrates that controlling the Bi/Sb ratio is an effective strategy to improve the thermoelectric performance of (Bi,Sb)${}_2$Te${}_3$ alloys.