The synthesis and the pressureless sintering of Bi₂Te₃ for thermoelectric application

Recently, interest in thermoelectric generation and cooling has increased; thus, placing greater emphasis on the thermoelectric material properties as well as on the manufacturing process. Bi2Te3 is a material that exhibits outstanding thermoelectric properties at room temperature, but it is manufactured in the form of monocrystalline ingots, which makes it difficult to process the material, and it is associated with significant material losses. In order to overcome this disadvantage, the pressureless sintering process has been investigated, but densification is difficult, and mainly the HIP and SPS methods are currently being studied. However, there is a lack of research on pressureless sintering without an additional driving force such as pressure or electric current application. In this study, a regular sintering furnace was modified to combine rapid sintering and ambient sintering in order to obtain dense Bi2Te3 pellets. First, Bi2Te3 powder was synthesized mechanochemically and a wet-milling process was established so that densification can occur easily during the sintering process. Using the synthesized powder, dense Bi₂Te₃ pellets were obtained after 10 min sintering at 520 °C after rapid heating at a rate of 120 °C/sec in a H2 and Te atmosphere. During the rapid sintering process, abnormalities were not produced from the oxidation reaction, and by preventing Te volatilization using Te atmosphere powder, no peculiar phenomena related to Te volatilization were observed in the pellets. Through this study, the feasibility of mass production of Bi2Te3 by the pressureless sintering process was investigated using rapid and ambient sintering.