Enhanced Cryogenic Thermoelectric Performance of Textured Bi_1–xSb_x Ribbons with Electronic Phase Transition

Bi 1– x Sb x alloys are promising cryogenic thermoelectric materials for generator and refrigeration devices at temperatures below 200 K. Herein, we prepared highly (00 l ) textured Bi 1– x Sb 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 (00 l ) orientation facilitate the alignment of the Fermi pocket of ribbon samples and cause a higher Seebeck coefficient compared with the nonoriented Bi 1– x Sb x bulk. Meanwhile, the Fermi level of Bi 1– x Sb 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– x Sb x alloys.