金属材料の熱電能

—電子構造による理解—

抄録

  Recently thermoelectric materials have attracted a great deal of interests because of their ability in the practical use as one of the most effective energy-saving technologies. Unfortunately, however, the guiding principle to produce a high-performance thermoelectric material has not been established yet, and the most of the efforts to improve their performance have been conducted based on the empirical ideas. This unfavorable situation is not caused by a delay in the theoretical works but by the approximations employed in the theories. In order to clarify the problems in the frequently employed approximations and the resulting formulas, new ideas to calculate the thermoelectric power in the metallic samples and the obtained rigorous formula are explained in detail on the basis of the Mott's consideration. It is stressed with a help of the resulting rigorous formula that the accurate determination of the electronic structure near the Fermi level is of great importance to quantitatively evaluate the thermoelectric power, because thermoelectric power is directly calculated from the spectral conductivity σ(ε) in which the electronic structure plays a key role as the most important parameter. A simple method using the rigorous formula with the numerical data of the electronic structure is introduced to quantitatively evaluate the magnitude and the temperature dependence of the thermoelectric power. For the electronic structure determination, two different methods are introduced; the high-resolution photoemission spectroscopy and the LMTO-ASA band calculation with reliable structure parameters determined by the Rietveld analysis. In this review paper, it is clearly demonstrated by use of some practical examples that the thermoelectric power in metallic systems can be quantitatively estimated from the electronic structure near the Fermi level, and that the method newly introduced in this paper should be employed in the material-design of the high-performance thermoelectric devices.