Effect of Ge substitution on carrier mobilities and thermoelectric properties of sintered p-type Ba8Ga16+xSn30-x-yGey with the type-VIII clathrate structure

Ge substitution for Sn in Ba8Ga16Sn30 was attempted in order to improve its thermoelectric properties. Since the melting point was raised by the substitution, the sintering temperature could be increased. The resultant sintered samples exhibited higher thermal stabilities and fewer trapping state densities at grain boundaries, which weakened grain boundary scattering for carriers. For example, the Ba8Ga16.4Sn25.0Ge4.6 and Ba8Ga16.9Sn19.8Ge9.3 samples had larger room temperature mobilities of 6.7 cm(2) V-1 s(-1) and 13.3 cm(2) V-1 s(-1), respectively, than that of 2.3 cm(2) V-1 s(-1) of the Ba8Ga16.6Sn29.4 sample. Consequently, these Ge-substituted samples had higher figures-of-merit maxima of 0.62 at 550 K and 0.63 at 600 K, respectively, than that of 0.36 at 500K for the Ba8Ga16.6Sn29.4 sample.