Thermoelectric properties of type-VIII clathrate Ba8Ga16Sn30 doped with Cu

The intermetallic clathrate Ba8Ga16Sn30 with type-VIII structure is one of the promising thermoelectric materials. We report on significant effects of Cu doping on both the crystal growth and thermoelectric properties of type-VIII clathrate Ba8Ga16Sn30. By using the Ga flux and Sn flux, respectively, the carrier type could be tuned as p-and n-types. The p-type single crystals were grown to approximately 6 mm in diameter, which is twice as large as that grown without Cu. The crystals were characterized by electron-probe microanalysis and powder X-ray diffraction and used for the measurements of the electrical resistivity, Seebeck coefficient, and thermal conductivity. The values of the dimensionless figure of merit ZT of the p-and n-type crystals reached 0.88 and 1.45 at around 500 K, respectively, the latter of which is the highest among all substituted systems of type-VIII Ba8Ga16Sn30. This enhancement of ZT is discussed in relation with the charge balance and modification of the band structure caused by Cu doping. (C) 2012 Elsevier B.V. All rights reserved.