| How to improve the thermoelectric properties of Bi2Te3-based flexible thin films is still a great challenge.Inspired by the fact that magnetic nanoparticles can significantly improve the thermoelectric properties of bulk materials,using screen printing combined with hot pressing technology,magnetic metal Ni nanoparticles(Ni-NPs)were creatively incorporated into BiSbTe-based flexible thermoelectric thin films,a series of magnetic nanocomposite flexible thermoelectric thin films were successfully prepared,and preparation process of incorporating magnetic nanoparticles into thermoelectric thin films at micro nano scale was explored.The effects of magnetic nanoparticles on the fine structure,electrical transport properties,magnetic properties and cooling performance of therm-electro-magnetic composite films were studied,and the physical mechanism of magnetic nanoparticles improving the transport properties of flexible thermoelectric thin films was revealed.At the same time,in order to solve the problem of measuring the in-plane thermal conductivity of thermoelectric thin films,a set of testing system based on Angstrom method is built independently,and the measuring feasibility has been verified.The main research contents and conclusions are as follows:(1)A series of xNi/Bi0.5Sb1.5Te3 composite magnetic flexible films were prepared by screen printing combined with hot pressing.Atomic resolution STEM shows that the orientation reaction occurs between Ni-NPs and Te in Bi0.5Sb1.5Te3.The resulting Te vacancy causes negatively charged VBi’" and BiTe’(SbTe’)anti-site defects and atomic-sized electric field in the magnetic flexible TE films further cause the acceleration movement and hopping migration of carriers.The transport performance test results show that the increase of carrier concentration is attributed to the anti-site defects,and the significant increase of mobility is due to the acceleration of microelectric field.The maximum power factor of magnetic flexible film doped with 0.lwt%Ni-NPs reaches 2.74 mW·m-1·K-2 at 300K,and the cooling performance is 250%higher than that of matrix.(2)The Ni-NPs were coated by SiO2 using Stober sol-gel method.TEM result shows that the thickness of SiO2 shell is 5 nm.A series of xNi@SiO2/Bi0.5Sb1.5Te3 magnetic flexible composite films were prepared by screen printing combined with hot pressing.The results of EPMA and magnetic properties show that the coated shell effectively controls the reaction between Ni and the matrix,which makes the composite magnetic flexible film ferromagnetic and enhances the magnetic scattering of carriers,which is the main reason for the improvement of Seebeck coefficient.The generation of BiTe’(SbTe’)increases the carrier concentration of magnetic flexible thin films slightly,and the atomic microelectric field increases the carrier mobility at the same time.Compared with epoxy/Bi0.5Sb1.5Te3 flexible thermoelectric films,the power factor of 0.1wt%Ni@SiO2/epoxy/Bi0.5Sb1.5Te3 reaches 1.92 mW·m-1·K-2 at 300 K,which is 13%higher than the matrix,the cooling performance is 50%higher than that of matrix.(3)Based on the Angstrom method,through the heat conduction simulation of film model,it is found that after heating the material with a constant source,the temperature rise curve is similar to the temperature rise stage of the sinusoidal curve.Based on this,a simpler test method is proposed,and a set of platform for simply testing the in-plane thermal diffusion coefficient of film is built.The minimum errors of Al,Cu and Brass are+9.7%,+4.7%,-7.3%respectively,and the errors are less than 10%,which verifies the feasibility of the platform device... |
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