Microwave-assisted Synthesis And Characterization Of Several Low-dimentional V/vi Group Thermoelectric Materials

Thermoelectric materials attract much attention because of its potential application for refrigerators or power generators. Recently, thermoelectric low dimensional structures such as quantum wells, quantum wires and quantum dots have been proven to have much high thermoelectric coeffcients according to both theoretical and experimental investigations. In this paper, low dimensional structures of Bi₂Te₃, Sb₂Se₃ and Te belonging to V/VI group materials (the best thermoelectric materials known at room temperature) were synthesized through a microwave-assisted method. Composition, microstructures and properties of power products synthesized were investigated. Formation mechanism of the products was studied. The main points were as follows:(1) Bi₂Te₃ hexagonal nanoplates have been successfully synthesized through the microwave assisted method. These Bi₂Te₃ hexagonal platelet-like crystals possess a fixed edge in the length of～0.5–2μm, and the thickness of these platelets is less than～100 nm. The effect of reaction time, ionic liquid, pH value, solvent and heating method were also studied. It was found that ionic liquid (BmimBr) played an important role in the formation of Bi₂Te₃ hexagonal nanoplates. The suitable quantity of BmimBr is in the range of 1-1.2 g and the suitable heating time is about 10 min. Thermoelectric parameters analysis indicated that these Bi₂Te₃ nanoplates possessing high Seebeck coefficient can improve thermoelectric property.(2) Sb₂Se₃ submicron tetragonal tubes and submicron spheres have been prepared by the microwave-assisted method. These submicron tubes possess tetragonal tubular structure with length in the range of 10-30μm, thickness in the range of 0.5-1μm and wall thickness in the range of 100-200 nm. Submicron spheres are 2-4μm in diameter. A novel transformation of Sb₂Se₃ microstructures from submicron tubes to submicron spheres during the microwave heating process was also found. After heating for 8-10 min, submicron tubes were generated. Prolonging the reaction to 30 min, submicron tubes were transformed into submicron spheres completely. The optical properties of Sb₂Se₃ submicron tubes and submicron spheres were characterized by UV–Vis diffuse reflectance spectroscopy, and the band gap (Eg) can be derived to be 1.161 and 1.173 eV, respectively.(3) Te nanotubes have been successfully synthesized through the microwave-assisted method. These Te nanotubes possess shuttle-like tubular structure with length in the range of 5-15μm, thickness in the range of 300-500 nm and wall thickness in the range of 100-150 nm. The surface of these nanotubes is decorated with spherical particles. It was found that reaction time and temperature played a significant role in the formation of shuttle-like Te nanotubes. When the reaction temperature was 150 oC, Te nanorods were obtained. When the reaction temperature was 170 oC, Te nanotubes with smooth surface were generated. Prolonging the reaction time, Te nanotubes decorated with spherical particles were obtained. The optical properties of Te nanotubes were characterized by photoluminescence spectrophotometer. Two strong PL emission peaks at 440 nm and 722 nm were observed with the excitation wavelength of 360 nm, which indicated that as-prepared Te nanotubes can give not only strong blue-violet emission but also strong red emission.