Specimens with a molar ratio of 100ZnO-2TiO2-2CoO-2Al2O3 (hereafter, ZTCA) were heat-treated by pulse current sintering (PCS) at a sintering temperature of 1423 K for 10 min and at applied pressures of 30-80 MPa. The thermoelectric characteristics of the obtained specimens were investigated from the viewpoint of their microstructure. On the basis of the resistivity-temperature characteristics of the specimens that were obtained by sintering ZTCA at 60 and 80 MPa, the resistance of the specimens locally increased at approximately 800 K during heating and the resistance during cooling remained higher than that during heating in the thermal history (hysteresis). The local increase and the hysteresis in the resistance were not observed for the specimen sintered at the low pressure of 30 MPa, which had large crystal grains and was densified, but they were observed for those sintered at the high pressures of 60 and 80 MPa, which had fine particles and were porous. In addition, a following problem has come up, that is, the local increase in the resistance of the ZTCA specimen observed at approximately 800 K may lead to a reduction in the power factor of the thermoelectric characteristics.
