High-purity hexagonal bismuth telluride (Bi 2 Te 3 ) nanoplates were prepared by a solvothermal synthesis method, followed by the fabrication of nanoplate thin films by the drop-casting technique. The Bi 2 Te 3 nanoplates exhibited a single-crystalline phase with a rhombohedral crystal structure. The nanoplates had a flat surface with edge sizes ranging from 500 to 2000 nm (average size of 1000 nm) and a thickness of less than 50 nm. The resulting Bi 2 Te 3 nanoplate thin films were composed of well-aligned hexagonal nanoplates along the surface direction with an approximate film thickness of 40 µm. To tightly connect the nanoplates together within the thin films, thermal annealing was performed at different temperatures. We found that the thermoelectric properties, especially the Seebeck coefficient, were very sensitive to the annealing temperature. Finally, the optimum annealing temperature was determined to be 250°C and the Seebeck coefficient and power factor were %300 µV/K and 3.5 µW/(cm&K 2 ), respectively.

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The thermoelectric properties of bismuth telluride (Bi2Te3) nanoplate thin films were estimated using combined infrared spectroscopy and first-principles calculation, followed by comparing the estimated properties with those obtained using the standard electrical probing method. Hexagonal single-crystalline Bi2Te3 nanoplates were first prepared using solvothermal synthesis, followed by preparing Bi2Te3 nanoplate thin films using the drop-casting technique. The nanoplates were joined by thermally annealing them at 250 °C in Ar (95%)–H2 (5%) gas (atmospheric pressure). The electronic transport properties were estimated by infrared spectroscopy using the Drude model, with the effective mass being determined from the band structure using first-principles calculations based on the density functional theory. The electrical conductivity and Seebeck coefficient obtained using the combined analysis were higher than those obtained using the standard electrical probing method, probably because the contact resistance between the nanoplates was excluded from the estimation procedure of the combined analysis method.

High-purity hexagonal Sb 2 Te 3 fine-platelets were successfully synthesized with high efficiency via a solvothermal route using a high precursor concentration with the assistance of glucose. The solvothermal synthesis was carried out at 180 °C for 16 h while the solution was stirred at 500 rpm. To clarify the role of the chemical compounds, we replaced glucose in the precursor solution with polyvinyl pyrrolidone (PVP). Hexagonal Sb 2 Te 3 platelets with a size of 3-6 μm and approximate thickness of 0.25 μm were obtained when an optimal amount of glucose (0.8 g) was used, and the production efficiency reached 90%. In contrast, the solvothermal synthesis route using various amounts of PVP produced mainly Te rods, and the production efficiency was as low as 40%. A possible reason for the successful growth of hexagonal Sb 2 Te 3 platelets via glucose-assisted solvothermal synthesis was the double role of glucose as a reducing catalyst as well as a surfactant.