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.

► Single crystals of type-VIII clathrate Ba8Ga16Sn30 doped with Cu were grown. ► The size of p-type single crystals is twice as large as that grown without Cu. ► The thermoelectric figure of merit ZT was assessed for 300 ⩽ T ⩽ 600 K. ► The ZT values of the p- and n-type crystals reach 0.88 and 1.45, respectively.