Research of High Performance Thermoelectric Materials with Nano-size Cages by focusing Random Host Structure of Quaternary Sn-based Clathrate Semiconductors

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We studied improve of a thermoelectric performance for Ba-Ga-Sn clathrate semiconductors with nano-size caged structure. The Sn-based clathrates have high abilities as high performance thermoelectric materials, in spits of a random structure of Ga and Sn in the host lattice. Therefore it is expected that transport properties are robust for additional element doping in Ba-Ga-Sn. In this study we tried to enhance the mobility of carrier by atomic doping to host sites or guest sites. In theoretical approaches we calculated the electronic structure by an ab-initio method and calculated the thermoelectric properties by using calculated band structure. In the calculation of the thermoelectric properties the semi-classical theory was used by the Boltzmann equation. In the experimental researches, new materials were synthesized, and a thermoelectric power, an electrical conductivity, and a thermal conductivity were measured.