Synthesis of Bi-Sb-Te-Se Thermoelectric Alloys

Reagent precursors metals Bi, Sb, Te, Se were ordered from Sigma-Aldrich Co., purity 5N grade. Quartz tubes were ordered from Technical Glass Products, Inc. with an outer diameter of 14 mm, inner diameter of 12 mm, and wall thickness of 2 mm for the ampoule. The raw materials were prepared with a Bi:Sb:Te:Se ratio of 1:1:1:2. The material total weight was 3 g mixed and crushed for 30 min, producing mixed fine powder. The powder was then loaded into the quartz tube to prepare for sealing. The inner tube wall was carbon-coated, preventing any possible reaction of the materials to the tube wall. Afterward, the tube was flushed with argon gas four times, displacing air, followed by vacuum pumping to reach a pressure below 10⁻⁶ torr to allow crystal growth in a vacuumed atmosphere. Finally, the tube was sealed by a hydrogen gas torch to a length of 6–8 cm.