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

¹CNR-ISTM, Istituto di Scienze e Tecnologie Molecolari, via Golgi 19, 20133 MILANO, ITALY

²Royal Institute of Technology, Materials Chemistry Division, Stockholm, Sweden

³Department of Chemistry and Biochemistry, University of California, Santa Barbara, CA 93106

⁴Department of Chemistry, University of Aarhus, DK-8000 Aarhus C, Denmark

⁵Legelab, Sweden

⁶German Aerospace Centre (DLR), Institute of Materials Research, Köln, Deutschland

⁷CIDETE INGENIEROS S. L., c/Anselmo Clavé 98, 08800 Vilanova i la Geltrú, Barcelona, Spain

⁸Department of Materials and Surface Chemistry, Chalmers University of Technology, SE‑412 96 Göteborg, Sweden

⁹NEDO Centre for Thermoelectric Engineering, University of Cardiff, UK

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.

1CNR-ISTM, Istituto di Scienze e Tecnologie Molecolari, via Golgi 19, 20133 MILANO, ITALY

2Royal Institute of Technology, Materials Chemistry Division, Stockholm, Sweden

3Department of Chemistry and Biochemistry, University of California, Santa Barbara, CA 93106

4Department of Chemistry, University of Aarhus, DK-8000 Aarhus C, Denmark

5Legelab, Sweden

6German Aerospace Centre (DLR), Institute of Materials Research, Köln, Deutschland

7CIDETE INGENIEROS S. L., c/Anselmo Clavé 98, 08800 Vilanova i la Geltrú, Barcelona, Spain

8Department of Materials and Surface Chemistry, Chalmers University of Technology, SE‑412 96 Göteborg, Sweden

9NEDO Centre for Thermoelectric Engineering, University of Cardiff, UK