Optimization On Microstructures And Transport Properties Of Fe Based Thermoelectrics Materials

FeSb2, FeSi2based thermoelectric materials was widely investigated due to their good thermoelectric performance, low cost and the characteristic of environmental friendly. But both of these two systems have their own inferiority. Based on the characteristics of these two kinds of materials, we carried out our study. The main and innovatory results are as follow:1. We introduced the hot deformation process into FeSb2bulks. We explored the influence of deformation temperature and deformation times for the effect of deformation process, and improved the thermoelectric properties of FeSb2bulks through the modulation on its microstructure. Lattice defects enhanced the phonon scattering effect, significantly reduced the lattice thermal conductivity of FeSb2bulks and improved its thermoelectric performance. The formation of texture lead to the anisotropy of thermoelectric transport properties in FeSb2bulks, made the ZT value of FeSb2along the pressing direction rises to0,021.2. We designed a method of synthesizing FeSi2·Mg2Si composite thermoelectric material by adding appropriate amount of Mg element in the FeSi2matrix with Si excess. The two-phase coexistence was found both from the XRD diffraction and SEM images. Based on this method, we synthesized the two-phase composites with different Mg2Si content to investigate the composite effect of Mg2Si and FeSi2. Besides we investigated the function of Co doping for the thermoelectric properties of FeSi2·Mg2Si composite, found that the composition of Mg2Si in FeSi2with5%Co doping was beneficial to improve its thermoelectric properties. This is due to the decrease in its thermal conductivity and increase in its Seebeck coefficient. The Co doping was also beneficial to improve its thermoelectric performance for its modulation on the electrical properties. The sample with best thermoelectric performance was the one doped by3%Co atoms on the Fe site.3. We designed a method of preparing the functionally graded thermoelectric materials in the application of high sensitivity thermoelectric sensors. Took the p-type FeSi2with Mn, Al double doping and n-type FeSi2with Co, Ni double doping as matrix, We prepared the functionally graded thermoelectric materials with good linear feature in its Seebeck coefficient. For the double doped FeSi2matrix, when its doping constituents changed regularly, so was their thermoelectric transport property. Based on this theory we designed the FeSi2functionally graded thermoelectric materials with different doping constituents. Result showed that, when the samples Co50:Ni50and Co87.5:Ni12.5was joined with the length ratio of2:1, its Seebeck coefficient maintained at around250μV/K. The fluctuation on the temperature range of400K to800K was less than5%, which showed very good application value.