| As the increasingly shortage of fossil energy, represented by oil, coal, and natural gas, and continually pollution of environment, it is time to give high priority to find a emerging, environment-friendly and renewable energy. Thermoelectric semiconductor material( thermoelectric material) is a environment-protection new energy material whose research and development has been widely concerned.Since Dr. Slack proposed the concept of "phonon glass-electron crystal"(PGEC), which provides a way to individually adjust three thermoelectric parameters and expands the direction of thermoelectric materials research,filled skutterudite which has a cage-like structure and heavy elements firstly verified PGEC concept from the experimental point of view, it shows that it has a high thermoelectric figure of merit and it is useful in cars exhausting pipe to convert the engine waste heat to electricity. At present, foreign and domestic scholars have been conducting lots of systematic research on n-type filled skutterudite, by a multi-atom composite filling, the maximum figure of merit ZT can reach 1.7. However, few research on the p-type filled skutterudite has been done. The maximum ZT value has been hovering around 1.0 for a long time. As we all know, a thermoelectric device need to match the n-type and p-type materials, so the research and development of high-performance p-type skutterudite material is the key to the actual application of the system.Herein, in this study, we focus on p-type filled skutterudite thermoelectricmaterials, using traditional solid-phase method and homemade melt spinning to get NdxFe3CoSb12 and NdxYbyFe3CoSb12 compounds, respectively. By these ways we discuss the influences rule of different types and content of filled atomics on the thermoelectric properties of p-type filled skutterudite compounds. This paper also deeply study the internal connections among microstructuresand the performance of thermoelectric. Besides, it emphasizes the melt spinning process on the structure, morphology and product superiority in improving thermoelectric performance. Finally we achieved better material components and higher performance. The contents and results of the research are as follows:(1)We use "melting-quenching- annealing- spark plasma sintering" method fabricate p-type single neodimium-filled skutterudite compound NdxFe3CoSb12(x= 0.8,0.85,0.9,0.95,1.0). The results of XRD show that the main phase of samples we made are skutterudite phase, and SEM images show the sintering samples are more dense, its theoretical density can reach 97%. In addition, the grain boundaries are more obvious, and the size is about 3 ~ 5um. The results showed that Nd0.9Fe3CoSb12 sample shows the highest ZT value reaches 0.8 at 760 K. It indicates that the p-type single filled skutterudite still can be improved in the study of thermoelectric materials in the middle temperature region.(2)In this study, we report the super rapid preparation of p-type skutterudites NdxFe3CoSb12(x=0.8,0.85,0.9,0.95,1.0) compoundsvia a home-made induction melting assembled inside the glove box followed by spark plasma sintering. The technology saves a lot of producing time, which is dramatically reduced from the original about a week(traditional solid-phase method) to less than 3h now. What's more, microstructure analysis shows that not only the uniformity of the sample has been greatly improved, but also the grain size has been drasticallly reduced, which reduces from a few microns to tens of nanometers.Theseconcomitant effects providesan extra mechanism to further reduce the lattice thermal conductivity. In addition, comparing with the sample of possessing same component with the traditional synthesis, its conductivity declines, but the seebeck coefficient improves in a certain degree, which leading to the electrical properties still has been significantly improved, finally. At last, bonding material electric transport properties, the ZT of sample Nd0.9Fe3CoSb12 reaches 1.0 at 760 K which is higher by 25% than the sample madeby traditional method..(3)Based on the advantages of melt spinning method, we continue to fabricate p-typebinary-filled skutterudites NdxYbyFe3CoSb12(x = 0.3,0.4,0.5,0.6,0.7) compounds by "melt spinning-spark plasma sintering" method, X-ray diffraction patterns shows we obtained skutterudite phase indeed. Through Scanning Electron Microscopy and Transmission Electron Microscopy observation the micro-structure of Nd0.3Yb0.7Fe3CoSb12 sample, we find numerous nano second phase YbSb precipitation. These nano-precipitates provides an additional mechanism for scattering long-wave phonon and reducing lattice thermal conductivity. Further, with the increase of filling fraction of atoms, the electrical properties of the material is increase, and the total thermal conductivity decrease to some extent. In conclusion, this method for preparing binary-filled skutterudites compounds not only shorten the time and reduce the cost of synthesis, but also greatly reduce the grain size, lower the lattice thermal conductivity, and improve the thermoelectric performance. Finally, these concomitant effects result in an enhanced thermoelectric performance with the dimensionless figure of merit ZT value up to 1.05 at760 K for Nd0.6Yb0.4Fe3CoSb12 MS-SPS sample, which is increased by 14% for average ZTave of the same component sample prepared by traditional method. |
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