Thermoelectric performance of large single crystal clathrate Ba8Ga16Ge30

A method for growing single crystals of the clathrate Ba 8 Ga 16Ge 30 has been developed and a suitable specimen prepared. The crystal with a diameter of 7 mm and a length of 46 mm was cut into discs, which were analyzed with respect to chemical composition, crystal structure and thermoelectric properties. Typical disc samples were found to be n-doped with the Seebeck coefficient increasing from -50 muV/K at 300 K to -185 muV/K at 900 K. The thermal conductivity was found to be close to 2 W/mK and only slightly decreasing with increasing temperature. The resistivity of the sample increased from 0.65 mOmegacm at 300 K to 1.8 mOmegacm at 900 K. Combining these results the dimensionless thermoelectric figure-of-merit, ZT (= TS 2/Rlambda), was found to increase from ZT = 0.08 at room temperature to ZT > 1.0 at 900 K. Preliminary data indicates that ZT appears to further increase with temperature above 900 K. These results emphasize the position of the Ba 8Ga 16Ge 30 clathrate as being in the same range of thermoelectric performance as the current state of the art materials at the medium to high temperature range