| In4Se3has been regarded as a promising thermoelectric (TE) material with high performance for its special layered structure and intrinsic low thermal conductivity. Although In4Se2.35single crystal had been reported a high ZT of1.48at700K in the b-c plane, the ZT value in the a-b plane is only about0.5at700K. Similar to the layered Bi2Te3-based TE materials, In4Se3single crystals are inclined to cleave owing to their weak van der Waals bonding, and polycrystalline In4Se3compounds are more favorable for further mechanical processing and thermoelectric applications. Therefore it is of significance to study and develop polycrystalline In4Se3In this present work, high performance of In4Se3-based materials were prepared through a combined process of mechanical alloying (MA) and hot pressing (HP). XRD, SEM, TEM, DTA, EDS, Hall and thermoelectric measurement have been employed to characterize their microstructure, chemical composition and thermoelectric properties. Effect of Fe substitution, Se deficiency and nanoparticles addition on microstructure and thermoelectric of In4Se3-based materials has been studied detailedly, the main results are summarized as follows:Starting from the element In and Se powders mixture, single phase In4Se3compound can be synthesized after ball milling for3h with a ball to powder mass ratio of20:1in a rotation velocity of400rpm. Dense polycrystalline In4Se3samples with homogeneous microstructure and the maximum ZT of0.39, can be obtained after hot pressing at723K for2hours under a pressure of120MPa.Fe substituted Polycrystalline FexIn4-xSe3(x=0-0.15) and Se deficient In4Se3-x (x=0-0.65) compounds with homogeneous microstructures were prepared by MA-HPed method and their thermoelectric properties were investigated. With the increase of x from0to0.15, the electrical resistivity and the absolute value of the Seebeck coefficient increased, while the thermal conductivity decreased first and then increased. The maximal dimensionless figure of merit ZT of0.44was obtained for the FexIn4-xSe3(x=0.05) sample at723K. Some In impurity was detected in bulk In4Se3-x samples. With increasing Se deficiency x, the carrier concentration increased, and the electrical resistivity and the absolute value of Seebeck coefficient of In4Se3-x decreased rapidly. While the thermal conductivity decreased first (0<x≤0.35) and the minimum thermal conductivity of0.54Wm-1K-1was obtained for the In4Se2.65sample at723K, and then increased (0.35x≤0.65). All of the In4Se3-x samples (x=0-0.65) had higher ZT than In4Se3, and In4Se2.65showed the highest ZT among Se deficiency In4Se3-x compounds, and the maximum ZT was0.94at723K.By thermal decomposition of the metal acetate precursors, In4Se3and In4Se3-x nanocomposites with Cu, Ni and Co) nanoinclusions have been prepared. The dispersive metal nanoparticles can effectively reduce the thermal conductivity due to their extra phonon scattering, thus, the ZT value was enhanced obviously in compared with the blank In4Se3and In4Se3-x samples. It shows Cu nanoinclusions are more effective in enhancing the thermoelectric properties than other metal nanoinclusions, and the maximum ZT of0.97and1.08were achieved at723K for the In4Se3and In4Se3-x samples with0.1wt%Cu nanoclusions, respectively.Nano-TiO2and nano-TiC dispersed In4Se2.65composites have also been prepared. It was found that nano-TiO2distributed homogeneously in the matrix when the content of TiO2is not more than0.5wt%. With increasing TiO2content, the electrical resistivity and the absolute value of the Seebeck coefficient increased, while the thermal conductivity decreased firstly and then increased. The0.5wt%TiO2dispersed In4Se2.65shows a maximum ZT of0.96at723K and a maximum flexural strength of63MPa at room tenperature. Nano-TiC particles distribute evenly in the matrix. With increasing TiC addition, the electrical conductivity and thermal conductivity decreased and an improvement was obtained in the TE performance. The composite with0.8wt%TiC addition present the maximum ZT value of0.98at723K and a maximum flexural strength of72MPa at room temperature. |
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