Nanostructured bulk YbxCo4Sb12 with high thermoelectric performance prepared by the rapid solidification method

High performance nanostructured bulk skutterudites YbxCo4Sb12 (x = 0.1, 0.2, 0.3) have been prepared by combining the melt spinning technique with spark plasma sintering (SPS). The effects of different linear speeds V of the spinning copper wheel on the microstructure and phase composition of ribbon samples and bulk materials are studied, and the influence of the nanostructure and Yb filling fraction on thermoelectric (TE) properties is investigated. The microstructure characterization results show that with increasing speed V, the ribbons possess finer nanostructure and a more homogeneous component distribution. As a result, the formation of the skutterudite phase during a brief SPS processing of the ribbons is very rapid. Moreover, the resulting bulk samples are single-phase, high density skutterudites with nano-scale size grains. The results of TE property measurements show that with the increasing linear speed V, i.e. with the formation of a finer nanostructure, the thermal conductivity of bulk samples decreases markedly without any significant effect on the electronic transport properties. In fact, we observe an enhancement in the Seebeck coefficient as the grain size decreases. The Yb0.3Co4Sb12 compound reaches its highest ZT of 1.22 at 800 K.