Study On Synthesis And Thermoelectrical Properties Of Skutterudite Materials

The skutterudite family of compounds own high Seebeck coefficient and low electr- ical resistivity, the thermoconductivity can also be reduced by filling the voids with rare- earth ions which is based on the unique crystal structure or by forming substitution solid solution. The improvement of ZT values aroses continually research interesting.The compounds of LayFe4-xNixSb12 possess the very special valence model and characters. First of all, we studied the influences of amounts of La and Ni to the phase compositions of LayFe4-xNixSb12 using XRD and DTA. The filling of La element is benefit to the forming of Skutterudite structure phase, and the lattice constant will enlarge. The addition element of Ni will make the gain of Skutterudite structure becomes more difficult. The decomposition temperature of LayFe4-xNixSb12 composition is about 770℃, which of CoSb3 is about 875℃, and the thermo stability is weakened.LayFe3.7Ni0.3Sb12 compounds is mainly p-type conduction(hole conduction), The Seebeck coefficient is improved with increasing La filling fraction, and we have got a high value of Seebeck coefficient when the filling fraction y is more than 1.7.LayFe3.7Ni0.3Sb12 compounds reveal metallicity, and the electrical resistivity is very low, but it will increase with the temperature increment. The thermoconductivity is lower than which of unfilling skutterudite compounds. LayFe3.7Ni0.3Sb12 compounds possese very high figure of merit ZT, The maximum of which of La1.7Fe3.7Ni0.3Sb12 is 0.4 at 700K.The time of hot pressing makes an obvious influence to thermoelectrical properties of LayFe3.7Ni0.3Sb12 compounds. The compound which is only hot pressed for 1.5 hours possess very low electrical resistivity, However, Its Seebeck coefficient is low and thermoconductivity is high. The compound which is hot pressed for 2.0 hours has excellent thermoelectric properties as it has high Seebeck coefficient, low thermoconductivity and moderate electrical resistivity. If the time of hot pressing increased to 2.5 hours, the Seebeck coefficient and electrical resistivity will both decrease. But the thermoconductivity will increase rapidly; the figure of ZT is lower.We also synthesize LayFe4-xNixSb12 compounds by two-step reaction process. Firstly, starting from elemental La and Sb, La-Sb compounds were successfully prepared by vacuum arc plasma evaporation (VAPE) technique. Then Fe, Ni Sb and La-Sb compounds were mixed according to atomic ratio (La: Fe: Ni: Sb=y: 4-x: x: 12), and gain the final production (Skutterudite phase) using MA+HP process, Compared with directly using MA+HP process, Oxidetion of La element and impurityies could be obviously decreased, the experimental operations could be simplified, and the thermoelectrical performance also be improved. The influence of La filling to the thermoelectrical performance have been studied, excessive filling is adverse.