| Thermoelectric(TE) material is a new kind of functional materials which make thermal and electrical energy to be converted. Skutterudite is the bulk thermoelectric material of superior performance for the middle temperature region, how to further enhance figure of merit ZT and mechanical stability of skutterudite has become an important research topic. In this paper, the skutterudite compounds CoSb2.79Te0.16Se0.05-xSx and CoSb2.79Te0.16P0.05-xSx(x = 0,0.01,0.025,0.04,0.05)were prepared by solid-state reaction combined spark plasma sintering technique, then the Te-Se-S and Te-P-S doping effect on the microstructure and electric-thermal transport properties were studied, which is aimed to achieving an electric-thermal cooperative control. In addition, we use the sample Co Sb2.79Te0.16S0.05 as the base material, and use TiN nanoparticles as the second phase by ultrasonic dispersion and high-energy ball milling technology, the nanocomposites CoSb2.79Te0.16S0.05 + x vol% Ti N(x=0.0, 0.5, 1.0) were obtained, and then the microstructure, electric-thermal transport properties and mechanical properties under different temperature conditions was explored. The main contents and results are as follows:(1) For the samples of CoSb2.79Te0.16Se0.05-xSx and CoSb2.79Te0.16P0.05-xSx(x = 0.0, 0.01, 0.025, 0.04, 0.05), all the samples were of single phase of CoSb3 skutterudite. Chemical compositions of Co Sb2.79Te0.16Se0.05-xSx obtained are basically homogeneous, and that the surface is consistent, although very small amounts of impurities are present in samples of x = 0.0, 0.025. The surface of sample CoSb2.79Te0.16P0.05 exists obvious defects, while it becomes more smooth and uniform with the incorporation of elements S. All the samples are observed to show similar temperature dependence trend of electrical conductivity, decreasing with the increasing temperature, a typical metallic conduction behavior. The absolute values of the Seebeck coefficients for all samples increase monotonically with the increasing temperature, but the increase tends to slow down when the temperature exceeds 750 K, resulting from intrinsic conduction. With the increase of the doping element S, the power factor for all samples decrease slightly, while the ZT values are gradually increased mainly attributed to the significant reduction of lattice thermal conductivity simultaneously. The sample CoSb2.79Te0.16S0.05 obtained the lowest lattice thermal conductivity of 1.14 Wm-1K-1 and highest ZT value of 1.25 at 800 K.(2) For all the the nanocomposites CoSb2.79Te0.16S0.05 + x vol% TiN(x=0.0, 0.5, 1.0), all the samples have intragranular-intergranular crystal structure mixed with no internal voids. With the increase of temperature, the conductivity decreases and absolute value of seebeck coefficient increases. For the TiN-dipersed samples, the thermal conductivity reduces while the thermoelectric figure of merit remains unchanged. As for the mechanical properties, the linear expansion coefficients of the samples rise with increasing temperature, the nano-TiN dispersed Skutterudites composites exist a significantly higher rate of increasing at high temperature. Flexural strength, compressive strength and fracture toughness of all samples decrease with increasing temperature, all the strength values at room temperature is higher than the strength values at high temperatures of 500℃. In addition, the mechanical properties of nano-TiN dispersed skutterudites is higher than that of none-TiN dispersed Skutterudites, indicating that nano synthesis technology is an effective way to improve the mechanical properties of Skutterudites. |
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