製備Bi0.5Sb1.5Te3熱電材料與熱電特性之研究

Abstract

This research focus on Bi0.5Sb1.5Te3 which is a room-temperature use thermoelectrical material. Higher ZT value can be achieved when used in room temperature. The material was prepared by using Zone melting process. In the beginning of the experiment, the smashed and screened powder was then conducted by cold pressing with omnipotent material experiment machine. During the cold pressing stage, observing the thermal-electrical properties by gradually increasing the pressure. The figure of merit was low due to the higher thermal conductivity. Therefore, in order to decrease the thermal conductivity, the powder was milled so that the carrier scattering possibility was increased. A higher ZT value was obtained from the 3-hour milling powder. However, the heat was generated accordingly during the milling which resulted in the decrease of electrical conductivity due to the oxidation of powder. To prevent the powder from oxidation, the de-oxidation process of powder was adopted but the result was not as good as expected. In another way to avoid the oxidation of powder, the N2 gas was introduced before milling. The conductivity and the ZT value were increased as a result. Furthermore, changing the compression temperature, applying hot pressing onto powder and wrapping the sample with graphite paper before sintering were considered. According to the final result, sample with milling for 3 hours under N2 atmosphere, pressing under 250 Mpa at 350oC for 10 minutes and sintering at 400oC for 2 hours can obtain the highest ZT value 0.51.