| Summary: | 碩士 === 國立彰化師範大學 === 物理學系 === 97 === Bismuth telluride based solutions have been widely used as thermoelectric materials in Peltier cooling modules and power generation. Improving thermoelectric performance of these materials is deeded for practical applications. It was reported that the substitution of Sb for Bi can enhance thermoelectric properties of Bi-Te system. Among them, the composition of Bi0.5Sb1.5Te3 showed the best thermoelectric performance. To prepare bulk Bi2Te3 based-compounds with good combination of thermoelectric and mechanical properties, many powder metallurgical methods such as mechanical alloying, hot pressing, hot-extrusion, ingot-extrusion have been extensively applied. However, these methods have some drawbacks such as time consuming, involving complicated procedures, high productions cost, contamination from milling container and balls, ect.
In this study, the hydrothermal method thoroughly by high-temperature and high pressure process was applied to prepare the powders of Bi0.5Sb1.5Te3 and Bi1.5Sb0.5Te3. In this method, ethylene diamine tetraacetic acid (EDTA) was uses as chelating agent, Borohydride (NaBH4) as a reducing agent, bismuth chloride (BiCl3), antimony chloride (SbCl3) and tellurium (Te) as starting materials. Deionized water was used as the solvent in the hydrothermal system. The bulk compounds were obtained using spark-plasma sintering (SPS) technique, applied for Bi0.5Sb1.5Te3 and cold-pressing sintering (CPS) one for Bi1.5Sb0.5Te3 samples and investigate their thermoelectric properties. The quality of the samples was checked by XRD, SEM measurements.
SEM observations and XRD FWHM analyses revealed that the SPS-bulk Bi0.5Sb1.5Te3 sample has large particles, small holes, and sharp XRD peaks. At room temperature, the resistivity, thermoelectric power, and thermal conductivity are 156 μV/K, 5.16 mΩ-cm, and 0.95 mW/K2, respectively.
The bulk sample of Bi1.5Sb0.5Te3, prepared by cold-pressing sintering, also showed the sharp XRD FWHM peaks. The sintered temperature at 340 ℃ gives the best thermoelectric properties. At room temperature, thermoelectric power, electrical resistivity, and thermal conductivity are 152 μV/K, 9.24 mΩ-cm, and 0.3 mW/K2, respectively and the ZT value is 0.25 at room temperature.
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