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Paper
Dalton Trans., 2010, 39, 1113 - 1117, DOI: 10.1039/b914382c
Preparation and thermoelectric properties of sintered type-I clathrates K8GaxSn46-x
Masahiro Hayashi, Kengo Kishimoto, Kazuma Kishio, Koji Akai, Hironori Asada and Tsuyoshi Koyanagi
Polycrystalline clathrate samples of nominal K8GaxSn46-x were prepared by the spark plasma sintering method to investigate their crystal structures, mobilities and thermoelectric properties. The samples almost had a single-phase type-I clathrate structure, and their relative densities reached as high as 98%. The room-temperature mobility of the K8Ga8Sn38 sample was 25 cm2 V-1 s-1, which substantially exceeded the reported mobilities of Rb- and Cs-containing Sn clathrates. Moreover, the mobility was larger than those of the type-I Ba8Ga16Sn30, which had more Ga substituting atoms in unit cell. A higher mobility might accordingly be achieved in thermoelectric clathrates with a smaller number of substituting atoms. Their electrical conductivities and Seebeck coefficients in the temperature range 300–450 K were typical of n-type doped semiconductors in the extrinsic region while their room-temperature lattice thermal conductivities were as low as
11 mW cm-1 K-1. The maximum dimensionless figure of merit ZT was estimated to be 0.27 at 490 K from the Seebeck coefficient of -262 
V K-1 and the electrical conductivity of 96 S cm-1 for the K8Ga8Sn38 sample with a carrier concentration of 2.9 × 1019 cm-3
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