Preparation And Thermoelectric Properties Of N-type CoSb₃ Based Materials With Sb-site Subsititution

Ranking in moderate temperature range, CoSb3 based thermoelectric material possessing great applying prospect, of which the optimization of thermoelectric properties is an international forefront research subject. Doping of partial Co or Sb-site substitution has also been widely studied to enhance the thermoelectric property. In previous studies, the substitution elements for Sb are mainly IVB or VIB-group elements (Te,Se,Ge and Sn) with very mean substitution fraction and almost sigle substitutions. In this research, we employed traditional solid-state reaction combining with spark plasma sintering technique to fabricate a series of single-substituted (Te), double-substituted (Ge,Te), triple-substituted (Ge,Te,Se) skutterudite compounds and the effects of substitution fraction on microstructures and thermoelectric properties are investigated systematically.For Co4Sb12-xTex (x=0.4,0.5,0.6,0.7) thermoelectric materials, the average particle size, carrier concentration and electrical conductivity exhibited a positive doping fraction dependence, and a maximum electrical conductivity of 16.29×104Sm-1 was obtained at 300K for Co4Sb11.3Te0.7. For the samples x=0.4-0.6, the values of the power factor were more than 4.0×10-3Wm-1K-2 as the temperature range in 650-800K, which were larger than the previous reports. Lattice thermal conductivity decreases monotonously over the whole investigated temperature and exhibits a negative doping fraction dependence except Co4Sb11.3Te0.7. The resultant dimensionless figure of merit ZT of all the samples increases monotonously over the whole investigated temperature, and a maximum value of 0.95 was achieved at 800K for Co4Sb11.4Te0.6.For Co4SbxGe5.9-0.5xTe6.1-0.5x(x=11,10,9,8,7,6) thermoelectric materials, the solubility limitations of IVB and VIB-group elements were expanded tremendously by Ge and Te codoping, the lattice parameter decreased linearly from 9.0252 (x=11) to 8.8995A (x=6). The behavior of electrical conductivity changed from semimetal-like character to semiconductor-like character along with the increase of substituting fraction. Thermal conductivities of all the specimens decreased first then increased with the increasing temperature. Furthermore, a minimumκL value of 1.56 Wm-K-1 was obtained at around 673K for Co4Sb8Ge1.9Te2.1. Co4Sb11Ge0.4Teo.6 showed the highest ZT=0.89 at about 773K.For Co4Sb11Ge1-x-yTexSey(x=0.70,0.75,0.80,0.85,y=0;x=0.60,0.65,0.70,0.75, y=0.1) thermoelectric materials, the average grain size of samples in group y=0 increased with the Te doping fraction, while it was relatively homogeneous and showed a weak dependence on Te doping fraction in group y=0.1. The electrical conductivity of the two groups of samples increased with the increase of Te doping fraction, but at diminishing rate. The thermal conductivity of the two groups of samples increased with the increasing Te doping fraction, and decreased first and then increased with the increasing temperature. Thermal conductivity of the samples doped with Se reduced significantly compared with that of the samples undoped with Se (dropped by 24%～28%(300K) and 17%～20%(800K)). A maximum dimensionless figure of merit of 0.99 was obtained at 775K for Co4Sb11Ge0.2Te0.7Se0.1, about 16% higher than that of Co4Sb11Ge0.2Te0.8 at the same temperature.