Enhanced Cryogenic Thermoelectric Performance of Textured Bi_{1- x}Sb_x Ribbons with Electronic Phase Transition

Bi_1-xSb_x alloys are promising cryogenic thermoelectric materials for generator and refrigeration devices at temperatures below 200 K. Herein, we prepared highly (00l) textured Bi_1-xSb_x (x = 0-0.05) ribbons by a melt-spinning technique and tuned its band structure with a Dirac electronic phase transition via Sb doping for improving the thermoelectric performance. The results indicate that the lamellar grains with (00l) orientation facilitate the alignment of the Fermi pocket of ribbon samples and cause a higher Seebeck coefficient compared with the nonoriented Bi_1-xSb_x bulk. Meanwhile, the Fermi level of Bi_1-xSb_x ribbons moves down by Sb doping, inducing the decrease of the carrier concentration and the increment of the Seebeck coefficient. Particularly, the Dirac electron phase is modulated when x reaches 0.04, which enlarges the carrier mobility and results in a well-maintained conductivity. Therefore, the optimized transport properties yield a large power factor of 61.1 μW·cm^-1·K^-2 at 140 K for the x = 0.04 sample, a significant 65% increase compared to the x = 0 ribbon. Besides, a planar thermoelectric device composed of 8 legs was assembled with the optimized ribbon, which produces a high open-circuit voltage of 39.8 mV. The output power maximum and the corresponding power density reach up to 402 nW and 125.7 μW·cm^-2 under a temperature gradient of 80 K, respectively. Our work suggests that modulating the Dirac phase transition can effectively enhance the thermoelectric performance of Bi_1-xSb_x alloys.