High thermoelectric performance of Cu substituted type-VIII clathrate Ba8Ga16-xCuxSn30 single crystals

Single crystalline samples of type-VIII clathrate Ba8Ga16-xCuxSn30 (0 <= x <= 0.033) were prepared by the Sn-flux method. Upon substituting Cu for Ga, the carrier mobility at 300 K increases twice while the carrier density stays in the range 3.1 - 4.2 x 10(19)/cm(3). Consequently, the electrical resistivity is decreased from 5.3 m Omega cm for x = 0 to 3.2 m Omega cm for x = 0.033. Irrespective of x, the Seebeck coefficient is largely negative and linearly changes with temperature in the range 300<600K. The thermal conductivity is in the range 0.68 - 0.74 W/Km at 300 K for all samples. The dimensionless figure of merit ZT for x = 0.033 reaches the maximum of 1.35 at 540 K. (C) 2011 American Institute of Physics. [doi:10.1063/1.3583570]