High thermoelectric performance of Cu substituted type-VIII clathrate Ba8Ga16–<i>x</i>Cu<i>x</i>Sn30 single crystals

Abstract

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 3.1−4.2×1019/cm3. Consequently, the electrical resistivity is decreased from 5.3 mΩcm for x = 0 to 3.2 mΩcm for x = 0.033. Irrespective of x, the Seebeck coefficient is largely negative and linearly changes with temperature in the range 300 &amp;lt; T &amp;lt; 600 K. 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.