Microstructure and Thermoelectric Properties of P-Type Bi 0.5Sb 0.5Te 0.5 Compounds Fabricated by Hot Pressing and Hot Extrusion

Abstract

Bismuth telluride (Bi{sub 2}Te{sub 0.5}) compounds have been used as thermoelectric cooling and power conversion materials, since they have a high figure of merit at room temperature and can be fabricated easily and cost effectively. The crystal structure of Bi{sub 2}Te{sub 0.5} at room temperature is rhombohedral (a = 0.438 nm and c = 3.049 nm). This crystal structure is composed of atomic layers in the order of Te/Bi/Te/Te/Bi/Te/Bi/Te/Te/... along the c-axis. The Te/Te layers are considered to be weakly bound with van der Waals-like forces. The electrical and mechanical properties along the directions parallel to the cleavage planes are better than those along the c-axis. The distinct cleavage planes are perpendicular t the c-axis. Owing to the cleavage features, the crystal has poor mechanical properties and fabricating of miniature thermoelectric modules is difficult. Many attempts were made by sintering to fabricate miniature modules without cleavage. However, the sintering technique is not effective because the figure of merit of sintered compounds is lower than that of single crystals. In this work, the authors fabricated the p-type Te-doped Bi{sub 0.5}Sb{sub 0.5}Te{sub 0.5} compounds by both hot pressing and hot extrusion and then investigated the microstructure and thermoelectric properties of the compounds.