Study on Creation of Novel Clathrate Semiconductors and Their Application to Thermoelectric Materials

为了实现节能和环境共存的社会，人们迫切希望找到新的热电能转换材料，通过该材料可以直接从大量的废热产生电力。我们已经研究了材料的设计和控制的热电性能在硅和锗为基础的笼形半导体，利用高自由度的笼状晶体结构，它包括多面体网络（主机），包括客户原子内的空隙。通过对主体晶格和客体位置的元素取代的新颖的结构操纵和控制，由于电子结构的修改和由于增强的声子散射导致的晶格热导率的降低，导致热电功率的显著增加。本研究发现的笼形半导体在材料设计上的发展将导致具有高转换效率的新型热电材料的产生。

It is highly desired to find new materials for thermoelectric energy conversion, by which the electric power can be generated directly from an enormous amount of waste heat, toward the goal of realizing the energy conservation and environmental coexistence society. We have studied the material design and the control of the thermoelectric properties in silicon- and germanium-based clathrate semiconductors, utilizing a high degree of freedom in the cage-like crystal structure which consists of polyhedral networks (host) including guest atoms inside the voids. The novel structural manipulation and control by elemental substitutions on host lattice and guest sites cause a significant increase of the thermoelectric power due to the modifications of the electronic structure and a decrease of the lattice thermal conductivity due to the enhanced phonon scattering. The development of clathrate semiconductors on the material design found in this study will lead to the creation of novel thermoelectric materials with high conversion efficiency.