Fabrication of Bi-Te based thermoelectric semiconductors by using hybrid powders

초록

BACKGROUND Thermoelectric semiconductors are functional materials using the effect of conversion between thermal energy and electric energy, and single crystal and unidirectionally solidified materials are widely used as thermoelectric semiconductors. These single crystal and unidirectionally solidified materials have excellent thermoelectric properties, whereas their bending strengths are 10~20MPa because of van der Waals bonds between Te-Te along c-axis. Powder metallurgy has been studied in order to improve the mechanical property, and powder metallurgy such as hot press and hot extrusion have been employed as fabrication process of thermoelectric semiconductors having a high bending strength in comparison with single crystal or unidirectionally solidified materials. Despite improvement of mechanical property, thermoelectric property is decreased by effect of oxidation, plastic deformation and decrease of orientation factor. In this study, we minimized the effect of oxidation and plastic deformation, and fabricated the thermoelectric semiconductors having excellent mechanical and thermoelectric property. RESULTS Orientation factors were increased with increasing ratio of coarse powders, whereas electric conductivities were decreased. Also densities and bending strengths were decreased because of lots of defects in matrix after sintering. Orientation factors were decreased with increasing ratio of fine powders, whereas electric conductivities, densities and bending strengths were increased. CONCLUSIONS In this study, we could obtain 70~80MPa of bending strength and 2.6~2.8×10-3/K of figure of merit by controlling mixture ratio of two different size powders. It is considered that thermoelectric properties were improved by using hybrid powders without degrade of mechanical properties.