成果報告書詳細
管理番号20160000000305
タイトル*平成27年度中間年報 エネルギー・環境新技術先導プログラム 超高性能バルク熱電材料(ZT20以上)の創製
公開日2016/5/20
報告書年度2015 - 2015
委託先名住友電気工業株式会社 学校法人トヨタ学園豊田工業大学
プロジェクト番号P14004
部署名イノベーション推進部
和文要約
英文要約Title: Advanced Research Program for Energy and Environmental Technologies / Development of super high performance bulk thermoelectric materials (ZT ≧ 20) (FY2015-2016) FY 2015 Annual Report

Thermoelectric generators (TEG), with which one can directly convert waste heat to useful electric power, have attracted considerable attention as one of the most efficient techniques leading to a low carbon, sustainable society. The figure of merit ZT of constituent thermoelectric materials is generally used as a measure for the efficiency of energy conversion in TE generators, and its value has not reached a large values exceeding 2 for the last half century, despite that ZT > 5 is required for automobile exhaust heat utilization system and ZT > 20 for power plant. This large gap between the required values and obtained values strongly let us believe that TEG is not usable in practical applications. We need to employ new, innovative techniques leading to a breakthrough for developing high-performance thermoelectric materials.
In this NEDO project, (i) we are going to propose a model of nanostructured thermoelectric materials capable of possessing a large ZT value exceeding 20, and try to prepare the samples characterized by the proposed nano-structure using some special techniques, such as liquid quenching, mechanical grinding, and/or molecular beam epitaxy. We shall also try to develop bulk materials consisting solely of the nano-structured grains for obtaining a large ZT value exceeding 5.

Contents and achievements of this project are as follows:
A) Modeling of atomic local arrangement and electronic structure for developing nano-structured high performance thermoelectric materials
As a consequence of theoretical considerations, we determined the conditions of electronic structure for obtaining a large value of A = S2σT / κel, that represents the upper limit of ZT for a given electronic structure. The materials should be a degenerate semiconductor, and it must be characterized by 1) a wide energy band gap of at least a several hundreds of meV, 2) a peak in electronic density of states within the energy range of several tens of meV from the chemical potential, and 3) presence of several bands in the same energy range. The peak in electronic density of states could be realized by the precipitation of nano-crystals in an amorphous semiconducting material.

B) Technological development of creating bulk materials
An amorphous bulk has been realized for magnetic material like NANOMET(c) by a melt-spinning method, however, it has not been realized yet for thermoelectric material. To develop amorphous thermoelectric materials, we have been searching lower-melting-point materials by changing the composition for Al-Mn-Si. By applying the melt-spinning method with some compositions of the materials, we succeeded in obtaining the amorphous ribbons of 2mm in width, showing halo pattern in X-ray diffraction.
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