Property Optimization Of P-type Rare-earth Filled Skutterudite Thermoelectric Materials

Thermoelectrical(TE) materials are functional materials for thermal-to-electrical energy conversion. An ideal TE material should not only have a high ZT but also be eco-friendly and low-cost. Among the most promising novel materials discovered, Filled skutterudites have received particular attention, suggested as the "phonon-glass/electron-crystal" materials with the good electrical transport properties of a crystal but the poor heat conduction characteristics of a glass. However, the thermoelectric behavior of p-type filled skutterudites could not be comparable with that of the n-type so far, because the heavy band feature in3d p-type skutterudites causes string electron-phonon interactions and reduces the power factor.In this thesis, for the characteristics and problems of filled skutterudite materials, the system study on them about the effect of different filler, different Fe/Co ratio or different ball-milling time. The main results are summarized as follows:The p-type skutterudite compounds of (Pr0.25Nd0.75)xFe3CoSb12have been successfully synthesized by levitation melting followed by annealing and spark plasma sintering. As a result, the system (Pr0.25Nd0.75)xFe3CoSb12is sensitive to (Pr0.25Nd0.75) fillers. The improvement in the thermoelectric properties was realized by the reduction in the lattice thermal conductivity when the voids are partially filled. The maximum ZT value of～0.83for (Pr0.25Nd0.75)0.76Fe3CoSb12was obtained at700K.The skutterudite compounds of (Pr0.25Nd0.75)0.8FexCo4-xSb12have been successfully synthesized by levitation melting followed by annealing and spark plasma sintering. When x≤1, the samples of (Pr0.25Nd0.75)0.8FexCo4-xSb12are n-type. And the samples of (Pr0.25Nd0.75)0.8FexCo4-xSb12are p-type when x>1. With increasing Fe content, the electrical conductivity, the power factors and the lattice thermal conductivity decrease and reach a minimum. While Fe/Co ratio was about3/1, the lattice thermal conductivity reached the minimum value of0.95Wm-1K-1. The maximum ZT value of-0.81for (Pr0.25Nd0.75)0.8Fe3CoSb12was obtained at700K.The samples of NdxFe3CoSb12prepared by levitation melting and spark plasma sintering are p-type semiconductor. The maximum ZT value of～0.77for Nd0.8Fe3CoSb12was obtained at700K.(Pr0.25Nd.75) is better than Nd as filler, because didymium metal (Pr0.25Nd0.75) is a "natural" double filler but is cheaper than the respective pure rare earths.Ball-milling time has great influence on the grain size. With the decrease of the grain size, the lattice thermal conductivity decrease. But the power factors decrease at the same time. As a result, the maximum ZT value is decreased after Ball-milling.