0.51.53Microstructure and thermoelectric properties of p-type BiSbTe fabricated by hot pressing

Abstract

Bi2Te3-based compounds are well known to be good thermoelectric materials for the applications near room temperature. The crystal has distinct cleavage planes perpendicular to the c-axis. Owing to the cleavage feature, the crystal has low mechanical properties and poor ability in micro-processing for fabricating the miniature thermoelectric modules and is inappropriate for mass production of thermoelectric modules. Many attempts were made by sintering to fabricate miniature modules without cleavage. However, sintering technique is not effective because the figure of merit of sintered compounds is lower than that of single crystals. The p-type Bi0.5Sb1.5Te3 compound doped with 4.0 wt% Te was fabricated by the hot pressing at the temperature range 380 to 440 °C under 200 MPa in Ar. The microstructure and thermoelectric properties of the compound were investigated. Optical microscopy, scanning electron microscopy, and X-ray diffraction were used to examine the microstructure. The microstructure wasrelatively dense. The density was increased with increasing the pressing temperature. The grains were preferentially oriented through the hot pressing and also the degree of preferred orientation was increased with the pressing temperature. It was also found that the figure of merit was increased with increasing the hot pressing temperature. The highest figure of merit was obtained at 420 °C.