Tunable Optimum Temperature Range of High-Performance Zone Melted Bismuth-Telluride-Based Solid Solutions

Bismuth-telluride-based solid solutions are unique, commercially available thermoelectric (TE) materials near room temperature for solid-state cooling, and the zone melting (ZM) technique is commonly applied to grow their commercial ingots with preferred orientation. Herein, we tailor the carrier concentration of zone-melted ingots by proper doping to adjust the optimum operating temperature for both solid-state cooling and low-temperature power generation at 300–500 K. A room temperature zT of ∼ 1.2 is obtained for both p-type and n-type ingots, and a maximum zT > 1.2 at 350 K in p-type Bi0.5Sb1.5Te3 + 2 wt % Te. Moreover, zT > 1.0 between 300 and 400 K is achieved for p-type, and zT > 1.0 between 300 and 475 K for n-type counterparts. It is found that the taper of the quartz tube affects the TE properties of Bi2Te3-based alloys. The different combinations of the growth rate with temperature gradient, 8 mm/h + 25 K/cm and 25 mm/h + 40 K/cm, contribute to equally high zT. In addition, the good homogeneity in both axial and radial directions implies the high quality of the ZM ingots in this work, which is significant for industrial manufacturing. These results are favorable for TE application in low-temperature power generation and show the possibility of improving the production efficiency of commercial bismuth-telluride-based solid solutions.