Microstructure control of Bi0.4Sb1.6Te3 thermoelectric material by pulse-current sintering under cyclic uniaxial pressure

The effect of the sintering holding time on the microstructure and thermoelectric properties of Bi0.4Sb1.6Te3 prepared by pulse-current sintering under cyclic uniaxial pressure was investigated. The sintering was performed at 400 °C under a cyclic pressure of 0 MPa and 100 MPa, and the holding time was varied from 0 to 60 min. The microstructure of samples, including grain size, hexagonal c-plane texture, and high-angle grain boundary, changed with holding time, that is, grain size and c-plane texture were enhanced and the high-angle grain boundary was reduced with increasing holding time. The thermoelectric properties changed corresponding to the change in the microstructures. The Seebeck coefficient was independent of the sintering parameters and had a value of approximately 200 μV/K. Nevertheless, electrical resistivity decreased with holding time because of the increase in the c-plane texture. As a result, the power factor was enhanced with increasing holding time. In contrast, thermal conductivity was insensitive with the holding time and had almost constant value. As a result, a dimensionless figure of merit of approximately 1 at 300 K was achieved with a large power factor of 4.3 × 10−3 W/K2m. Therefore, in the PCS-cyclic process, the holding time is an important sintering parameter for controlling the microstructure and electrical properties of Bi0.4Sb1.6Te3 thermoelectric materials.