Colloidal Synthesis And Thermoelectric Properties Of Ternary Copper-based Nanomaterials

Colloidal synthesis routes can produce the novel nanostructures at relative low temperatures and using short reaction times. Boosted by their promising application in photocatalysis, photodetector and thermoelectric applications, great progresses have been achieved in colloidal synthesis of metallic and chalcogenide nanostructures in the last decade. In this dissertation, three different Cu-based nanostructures have been synthesized by colloidal synthesis process, and we avoid using the hazardous, unstable alkylphosphines as the organic precursor solution. Furthermore, thermoelectric properties of as-synthesized nanomaterials have been investigated.The main research contents of this dissertation are as follows:Fistly, Cu2SnSe3(CTSe) nanocrystals was successfully synthesized by a "hot-injection" protocol in the presence of oleylamine (OLA). Selenium powder dissolved in the mixed solution of OLA and dodecanethiol (DT) at room temperature were injected into a hot solution of OLA, including copper chloride, tin chloride, at a given reaction temperature. The structure, composition and morphology of the synthesized samples were characterized via using powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and field-emission scanning electron microscopy (SEM). The results revealed that the as-synthesized nanocrystals were single phase polycrystalline with cubic crystal structure, and high monodispersity with an average diameter of5nm. Furthermore, the thermoelectric properties of these dense materials compacted from nanocrystals with the temperature range from300K to598K were studied. All the electrical and thermal transport properties have been measured along the perpendicular and parallel to the hot press direction for evaluating the anisotropic properties of CTSe. At last, the results exhibit a promising figure-of-merit ZT value of-0.34along the perpendicular direction at598K.Secondly, a novel solution-based synthesis of monodispersed Cu3SbSe4(CASe) nanoscrystals with narrow size distributions and controlled composition has been described using the same Se precursor; the thermoelectric properties of these dense materials compacted from nanospheres by spark plasma sintering (SPS) have been investigated for the first time. The structure, composition and morphology of the synthesized samples were characterized via using powder XRD, XPS, TEM and SEM. The results revealed that the as-prepared nanocrystals were tetragonal crystal structure, and high monodispersity with an average diameter of18±1nm. The formation of pure stannite CASe nanocrystals was found to be highly dependent on the reaction temperature, ratios of reactants, time and precursor type. Therefore, we discussed all kinds of reaction conditions and got the best one. Furthermore, CASe is demonstrated to show excellent thermoelectric properties. With the help of good power factor and relatively low thermal conductivity, the dimensionless figure-of-merit ZT reaches a peak value of0.69at673K, and it demonstrates that the prepared CASe could potentially be useful for efficient thermoelectric materials.Thirdly, the ternary p-type CuFeSe2(CISe) represents a new class of Ⅰ-Ⅲ-Ⅵ2family of compound semiconductors that belongs to the narrow band gap material. It has attracted widespread research interest in the development of potential applications for photovoltaics and photodetector devices. In this part, we report that the sythesis of monodispersed CISe nanocrystals with an average diameter of8nm by colloidal method at first, then the thermoelectric properties of these dense materials compacted from CISe nanocrystals with the temperature range from298K to613K have been discussed, and the results exhibit a lower figure-of-merit ZT, compared to that of the former two type nanostructures at613K. However, it is believed that further enhancement of the thermoelectric properties can be obtained through proper doping, fine tuning the chemical composition and better controlling the grain size during the compacting procedure.