(Fe_<1-x>,Ti_x)_2O_3の熱電特性と電子構造

概要

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We have investigated α-Fe2O3 system as the oxide thermoelectric (TE) materials to convert energy from temperature differences to electricity. Generally, an oxide TE material has a large thermoelectric power (Seebeck coefficient) and lower thermal conductivity. However, this system has a large electrical resistivity (more than 10−5 Ωm) and thermal conductivity (35 Wm−1K−1 at room temperature) which are not good properties for TE material. The aim of this research is to reduce thermal conductivity mainly, and to reduce electrical resistivity as well. For our approach we calculate the electronic structures to know around Fermi energy level and bonding characteristics using ab-inito calculation with discrete variational Xα method (DV-Xα). DV-Xα is one of molecular orbital methods. Actual material of (Fe1-x, Tix)2O3 system was also formed by powder metallurgical method by adding TiO2 to α-Fe2O3. As the one of calculation results, the impurity level existed in an energy gap (about 3.5 eV) which lessen the energy gap. Electron behaviors are covalent according to the calculation results and combination of Fe and Ti seems to be better in terms of reduction-oxidation potential of them. Thermal conductivity reduced down to 3 Wm−1K−1 for 5 mol% specimen at 600 K and higher temperature. Furthermore, dimensionless figure of merit (ZT) was 0.04.
社団法人粉体粉末冶金協会の論文
2007-05-15