Thermoelectric properties of Co(MxSb/sub 1-x/)3 (M=Ge, Sn, Pb) compounds

The thermoelectric properties of CoSb/sub 3/, which was doped with IV elements of Sn, Ge and Pb, were investigated in order to improve the p-type thermoelectric performance of non-doped CoSb/sub 3/. Co(M/sub x/Sb/sub 1-x/)/sub 3/ (M=Ge, Sn, Pb) compounds were prepared by hot-pressing. The solubility limit of these dopants was determined from measurements of the X-ray photoelectron spectroscopy (XPS). The solubility limit of Ge and Sn are estimated to be about 1.4 and 2.4%, respectively, while Pb hardly substitutes for Sb. The Hall measurements reveal that the maximum carrier concentrations at room temperature were 1.5/spl times/10/sup 19/ cm/sup -3/ for Ge and 2.9/spl times/10/sup 19/ cm/sup -3/ for Sn. The change in the mobility with x can be explained qualitatively by taking account of conduction of both holes and electrons in doped CoSb/sub 3/. The electrical conductivity /spl sigma/ and Seebeck coefficient S of these samples were measured in the temperature range from 300 to 800 K. The p-type conduction is achieved in the whole temperature range by introducing Ge and Sn in CoSb/sub 3/. The values of the power factor S/sup 2//spl sigma/ for Co(Sn/sub x/Sb/sub 1-x/)/sub 3/ with x=1% are of the order of 10/sup -5/W/cmK/sup 2/ and 2/spl sim/10 times as high as those of the non-doped CoSb/sub 3/ in the wide temperature range.