Preparation And Thermoelectric Properties Of P-type Fe-based Skutterudite Nanocomposite Thermoelectric Materials

Filled skutterudite with good thermoelectric transport performance and excellent mechanical properties is currently one of the most promising intermediate temperature thermoelectric（TE）materials.In order to prepare efficiently filled skutterudite-based TE devices,it is important to have p-and n-type filled skutterudite TE materials with matching performance.However,the current TE performance of p-type Fe-based filled skutterudite materials is worse than that of n-type filled skutterudite materials.Therefore,how to obtain high-performance p-type Fe-based filled skutterudite materials is the key to preparing high-efficiency skutterudite-based TE devices.This thesis first obtains a p-type Fe-based filled skutterudite matrix material with excellent performance by optimizing the preparation temperature,and then introduces magnetic nanoparticles into the matrix material to prepare a magnetic nanocomposite material.The electron-phonon transport can be synergisticly regulated with magnetic nanoparticles at the nanometer-mesoscopic scale,which can further improve the TE performance of the matrix material.The main research results are as follows:Ce_1.25Fe₄Sb₁₂ skutterudite samples with different quenching temperatures（1223K,1273 K,1323 K,1373 K and 1423 K）were successfully prepared by the traditional melting-quenching-annealing process combined with SPS sintering technology.XRD and EDS analysis results show that all samples are composed of main phase skutterudite,Fe Sb₂,Ce Sb₂,Sb and other impurity phases.Compared with other samples,1423 K sample has less impurity phase content and more micro-nano pores,so it has higher power factor and lower thermal conductivity,showing excellent TE performance.It has a maximum ZT value of 0.59 at 675 K.This shows that the formation of impurity phases can be reduced by optimizing the quenching temperature,and a high-performance porous Ce-filled Fe-based skutterudite thermoelectric material can be obtained.The BaFe₁₂O₁₉ nano-suspension was obtained by chemical co-precipitation,high-energy ball milling and liquid-solid sedimentation separation technology.Then the BaFe₁₂O₁₉ nano-suspension was mixed with Ce_1.25Fe₄Sb₁₂ matrix material ultrasonically,and the x BaFe₁₂O₁₉/Ce_1.25Fe₄Sb₁₂（x=0%,0.05%,0.15%,0.25%and0.35%）magnetic nanocomposite TE materials were successfully prepared by the SPS sintering process.XRD analysis results show that the addition of magnetic nanoparticles does not change the phase composition of the matrix.FESEM analysis shows that the increase of BaFe₁₂O₁₉ nanoparticles will lead to an increase in the number of micro-nano particles on the surface of crystal grains and grain boundaries of the matrix.These micro-nano particles can scatter heat-carrying phonons,thereby reducing the lattice thermal conductivity of the material.The magnetic measurement results show that the coercive force of the composite material is improved compared with that of the matrix material,which is due to the introduction of hard magnetic BaFe₁₂O₁₉ nanoparticles.In addition,the introduction of an appropriate amount of BaFe₁₂O₁₉ nanoparticles can significantly suppress the deterioration of the high-temperature performance of the matrix.By optimizing the content of BaFe₁₂O₁₉nanoparticles,the maximum ZT value of the x=0.25%sample at 675 K is 0.63,which is about 15%higher than that of the matrix.The Co nano-suspension prepared by the hydrothermal method and Ce_1.25Fe₄Sb₁₂matrix material were ultrasonically mixed,and then the x Co/Ce_1.25Fe₄Sb₁₂（x=0,0.1%,0.2%,0.3%and 0.4%）magnetic nanocomposite TE materials with uniformly dispersed Co nanoparticles were successfully prepared by the SPS sintering process.The analysis of XRD results shows that the introduction of Co magnetic nanoparticles does not change the crystal structure of the matrix.FESEM and EDS analysis confirmed that Co nanoparticles were uniformly dispersed on the grain boundaries and grains of the matrix.The addition of Co magnetic nanoparticles may produce three thermo-electromagnetic effects:charge transfer from magnetic nanoparticles to the matrix;multiple scattering of electrons by magnetic fluctuations;and enhanced phonon scattering caused by magnetic fluctuations and the nanostructure itself.These effects can significantly enhance the electrical and thermal transport properties of nanocomposites.By adjusting the content of Co nanoparticles in the matrix,the maximum ZT value of the x=0.3%sample at 675 K is 0.62,which is about 24% higher than that of the matrix.