Microstructure and thermoelectric properties of CoSb3 synthesized by MA-SPS method

Single-phase polycrystalline CoSb3 skutterudite was prepared through a new combination of mechanical alloying (MA) and spark plasma sintering (SPS). In order to investigate the influence of MA conditions on the microstructure and thermoelectric properties, MA synthesis were carried out under various conditions with different milling times. The powder sample MAed for 6h still consisted of metal Sb, and then transformed to CoSb3 with a little amount of metal Sb and CoSb2 phases after MA for 15h. Further prolonging the MA time resulted in the decomposition of CoSb3 to CoSb2 phase. The average grain size of the SPSed samples decreased from 650nm to 250nm as MA-time was prolonged from 6 to 24h. Lattice parameters estimated form XRD patterns increase with the increasing MA time. All samples SPSed at 600 degrees C for holding 5 min show an n-type conduction. The electrical resistivity was 1030, 895, 410, 260 mu Omega m for the samples from the MA-derived powders with MA-time of 6, 15, 24 and 33h at room temperature, respectively, then reduced to 60 mu Omega m at 400 degrees C for all samples. An optimum MA time is 24 h in which the sample shows the highest power factor 612 mu W/m*K-2 at 150 degrees C.