Effect of Cyclic Uniaxial Pressure in Pulse-Current Sintering on Microstructure of Bi₂Te₃-Based Thermoelectric Materials

Abstract

Various cyclic uniaxial pressure patterns have been applied to a powder of Bi_0.4Sb_1.6Te₃ thermoelectric material during the pulse-current sintering process. The cyclic uniaxial pressure pattern (0 MPa to 100 MPa) was varied by changing the number of pressure cycles and the ratio of the pressing time to the time during which no pressure was applied (i.e., pressing time/pressureless time). Sintering was performed at 400°C for 10 min in vacuum. Electron backscattered diffraction analysis revealed that both the number of pressure cycles and the pressing time ratio strongly affected the microstructure of the sintered materials. Increasing the number of pressure cycles led to a monotonic increase in the intensity of the c-plane orientation. Increasing the pressing time ratio also enhanced the intensity of the c-plane orientation, although the intensity of the c-plane orientation decreased at larger pressing time ratios. These results indicate that constant pressure and pressureless sintering are not effective for attaining c-plane orientation and that the cyclic uniaxial pressure pattern is important for controlling the microstructure of the sintered material. Consequently, the thermoelectric properties of sintered materials could be enhanced by varying the cyclic uniaxial pressure pattern.