Papers by Keyword: Aurivillius Compound

Abstract: Thermoelectric generator is expected as an independent source, an energy converter for co-generation with Refuse Derived Fuel (RDF) and so on. Thermoelectric materials were required high Seebeck coefficient, low electrical resistivity and low thermal conductivity. Thermoelectric oxides are suitable at the high temperature range because of chemical stability. Authors focus attention on Aurivillius compounds. The Aurivillius compounds consist of Perovskite layers and Bi-O layers. It is expected that nano-layered structure shows high Seebeck coefficient due to the quantum confinement of electron in Perovskite layers. It was reported that the Seebeck coefficient of Aurivillius phase Bi₂VO_5.5 was high value of -28.3 mVK^-1 at 1010 K, and the electrical resistivity of the one was also high value of 0.033 Ωm at 1010 K. We investigated about element substitution effects at V site on thermoelectric properties. Bi₂V_1-xM_xO_5.5 (M=Cu, Cr, x=0, 0.05, 0.1, 0.2) were prepared by solid-state reaction and hot pressing. From the results of the electrical resistivities and the Seebeck coefficients, Cu and Cr behaved as acceptor to Bi₂VO_5.5. Cr was effective for reducing the thermal conductivity of Bi₂VO_5.5. The maximum value of dimensionless figure of merit for Bi₂VO_5.5 was 0.06 at 910 K.

Abstract: Research and development of thermoelectric generators have been actively carried out to use waste heat. It is well known some p-type oxides show high thermoelectric performance. However, an n-type oxide with high performance has not been found. An n-type CaMnO3 is a promising material because of its high Seebeck coefficient. The electrical resistivity of this oxide is, however, too high to use it practically. Not only high Seebeck coefficient but also low electrical resistivity is required for practical use. At first, we investigated the effects of element substitution in order to decrease the resistivity. N-type CaMn0.9M0.1O3 (M=Cu, In) compounds were prepared by solid-state reaction and hot pressing. The maximum value of power factor for CaMn0.9In0.1O3 was 0.204 mWm-1K-2, which was the largest of all specimens at 673 K. This value was, however, not enough to use it practically. Secondly, we focus attention on Aurivillius compounds. The Aurivillius compounds consist of Perovskite layers and Bi-O layers. We expect that this crystal structure shows large Seebeck coefficient due to the quantum confinement of electron in Perovskite layer. Bi2VO5.5 with Aurivillius structure was prepared by solid-state reaction and hot pressing. The Seebeck coefficient of Bi2VO5.5 decreased with increasing temperature and was positive value below 600 K and was negative value above 600 K. The power factor of annealed Bi2VO5.5 showed the highest value of all specimens at the temperature range above 800 K.