Thermoelectric elements using environment-friendly materials with high thermoelectric
conversion efficiency and of these thermoelectric elements can be increased by using a structure
combining n-type and p-type semiconductors. From the above point of view, attention was
directed at ZnO as a candidate n-type semiconductor material and investigations were made. As the
result, a dimensionless figure of merit ZT close to 0.28 (1073K) was obtained for specimens
produced by the PCS (Pulse Current Sintering) method with addition of specified quantities of TiO2,
CoO, and Al2O3 to ZnO. It was found that the interstitial TiO2 in the ZnO restrains the grain growth
and CoO acts onto the bond between grains.
BaTiO3 ceramics including 0.2mol% Ta2O5, increases its compactness due to the agglomeration during the first sintering period, but the compactness decreases with decreasing the particle size of the starting BaTiO3. The inhomogeneous formation of necks among the particles and the inconsistent growth rate of neck were observed. This seems to result in a wide distribu tion of the particle size and the size of the pores among the particles. In the middle sintering period the agglomeration will proceed with disappearance of the voids in the cross-linked structure by adhesion among the particles. Eventually the compact ness of the ceramics increases, however, the agglomerating region are quite different in size. In the final sintering period the local formations of abnormally grown particles were observed in the agglomerating region. The inhomogeneous mixing of large and small particles has the responsibility to form various pores having many different diameter and results in a de crease of the density. In conclusion the decrease in the density seems to be due inhomogeneous distribution of pore caused by the rapid rearrangement of the fine particles and the irregular formation of the necks among the particles .
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