Thermoelectric characteristics of solvothermally prepared (Bi,Sb)2Te3 mats containing nanosize of sheet-tubes

We report thermoelectric characterization of Bi_2-xSb_xTe₃ (x = 0.5, 1.0, and 1.5) synthesized by a solvothermal method using DMF as solvent. For Bi₂Te₃, the size of the edge and thickness of the hexagonal nanoplatelets are 200-250 nm and 20-25 nm, respectively. Bi₂Te₃ nanosheets appear to grow epitaxially from the surface of the Te tubes, which forms in the first step and acts as the template for the formation of the nanostructure. Upon doping with Sb, the morphology of Bi_1.5Sb_0.5Te₃ changes to a cluster of nanoparticles with the size of ~100 nm. The morphology of Bi_0.5Sb_1.5Te₃ consists of mainly nanoplatelets with a size of less than 100 nm and warped nanosheets growing along the Te tube. The nominal composition of Bi₂Te₃ mats containing sheet-tubes shows a negative thermopower of ca. -94 muV/K at 280 K, whereas Bi_0.5Sb_1.5Te₃ shows a positive thermopower of ca. 200 muV/K at 280 K.