Abstract
We sintered a material composed of the raw material ZnO, the doping agent Al2O3 for resistivity reduction, and a sintering aid in which TiO2 and CoO are mixed at a predetermined ratio by pulse current sintering at 80 MPa and 1373-1423 K for 10 min, and studied its thermoelectric properties and microstructure. From the microstructures of a sintered material, we confirmed that TiO2 suppresses the grain growth, CoO promotes the grain growth and the development of intergrain neck connections. Because a decrease in resistivity of the material was observed when CoO was added to the specimen, the decrease in resistivity is considered to be caused by intergrain neck connections which seem to form a conduction channel. Moreover, from the analysis of EPMA, Al2O3 was localized in 100ZnO-2Al2O3 (ZA); however, Al2O3 was observed in the entire region of 100ZnO-2TiO2-2CoO-2Al2O3 (ZTCA). From the XRD analysis of these two specimens, the spinel phase of ZnAl2O4, which causes high resisitivity, was more prominent in ZA than in ZTCA. Among the materials studied, ZTCA showed the best thermoelectric properties and a dimensionless figure of merit (ZT) of approximately 0.28 was obtained at 1073 K.
