Thermoelectric performance of large single crystal clathrate Ba8Ga16Ge30
L. Bertini1, K. Billquist2, D. Bryan3,M. Christensen4, C. Gatti1, L. Holmgren5, B.B. Iversen4, E. Mueller6, M. Muhammed2, G. Noriega7, A.E.C. Palmqvist8,D. Platzek6, D.M. Rowe9, A. Saramat8, C. Stiewe6, G.D. Stucky3,G. Svensson8, M. Toprak2, S.G.K. Williams9,Y. Zhang2
A method for growing large single crystals of the clathrate Ba8Ga16Ge30 has been developed. Several samples were cut from the as-grown single crystal ingot (diameter 8 mm and length 46 mm) and were analyzed for chemical composition, crystal structure and thermoelectric properties. These samples were found to be n‑doped with average Seebeck coefficients increasing from –60 mv/K at 300 K to –185 mv/K at 900 K. The thermal conductivity was found to be close to 2 W/mK and slightly decreasing with increasing temperature. The resistivity of the sample increased from 0.65 mW/cm at 300 K to 1.8 mW/cm at 900 K. Combining these results, the dimensionless thermoelectric figure-of-merit ZT was found to increase from 0.08 at room temperature to ~ 0.90 at 900 K, and did not show signs of reaching a maxima up to 900 K. These results indicate that the thermoelectric performance of the Ba8Ga16Ge30 clathrate is within the same range as current state of the art materials in the medium to high temperature range.