Microstructural Engineering for Power Factor and ZT Optimization in Cu Alloyed n‑Type Bi_2-x Sb _x Te₃ Thermoelectric...

Bismuth telluride (Bi₂Te₃) alloys are widely used thermoelectric (TE) materials for near-room-temperature energy conversion. The performance of TE devices in this range critically depends on n-type Bi₂Te₃ alloys for performance parity with that of their p-type counterparts. This study presents a strategy for tuning the thermoelectric properties of selenium-free n-type Bi_2-x Sb _x Te₃ (BST) through controlled copper (Cu) alloying. Cu incorporation via ball milling enhanced the Seebeck coefficient but reduced electrical conductivity due to the formation of coarse Cu-rich precipitation. Subsequent melt-spinning recovered conductivity and promoted uniform Cu dispersion while inducing beneficial point defects and lowering lattice thermal conductivity. These combined effects shifted the peak ZT value toward room temperature, achieving better alignment with the operational range of the p-type materials. A four-pair TE device fabricated with 0.1 wt % Cu alloyed BST (melt-spun) demonstrated a 20% increase in output power at T _hot = 450 K compared to the pristine sample. This work demonstrates the role of Cu alloying and microstructural engineering in optimizing n-type BST for efficient thermoelectric power generation.