Progress of high efficiency thermoelectric oxide ceramic materials generated at high temperature

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1.Trial manufacture of an apparatus for the measurement of Hall coefficient at high temperature The apparatus was trial manufactured for the measurement of Hall coefficient up to 1000 ﾟC under various oxygen partial pressure. Because the individual measurement of carrier concentration and the mobility is essential for the understanding of the conductive mechanism of the material at high temperature. The disc-shape sample with 0.3-0.4 mm in thickness was prepared by conventional sintering methods and was shaped into like a clover. The Hall coefficient of (La,Sr)FeO_3 was measured by van der Pauw methods. The measurement was performed by positive and negative current direction under the two magnetic field direction to cancel the effect of sample shape,.2. The thermoelectric power of Sb doped BaSnO_3 The electrical conductivity of BaSnO_3 increased from 10^<-8> to 10^2 s/cm by substitution of Sn to Sb. Among Ta, Nb and Sb, Sb is the most effective substitute material for the improvement of the electrical conductivity. From the results of electrical conductivity and Seebeck coefficient measurements, it was clarified that the conduction mechanism of Sb doped BaSnO_3 was extrinsic conduction caused by impurity atom up to 500ﾟC, and was intrinsic one above 500ﾟC. From the result of the present study, it will be expected that this material has high thermoelectric power at higher temperature.3. Research of the materials with higher thermoelectric power The degree of thermoelectric power is the product of electrical conductivity by Seebeck coefficient. The investigation of the Seebeck coefficient will be more important for the research of the materials with higher thermoelectric power. Therefore the understanding of not only the carrier concentration but also the scattering factor and density of the states will be necessary.