Solvothermal preparations of nanocrystalline Bi 2 Te 3 powders and the study on their characterizations
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Solvothermal preparations of nanocrystalline Bi2Te3 powders and the study on their characterizations Xiaohua JI, Xinbing ZHAO, Yanhua ZHANG, Bo-hui LU, Hualiang NI (State Key Laboratory of Silicon Materials, Zhejiang University, Hangzhou 310027,China) [Abstract] Bi2Te3 nanoparticles of 15~25nm were prepared via solvothermal processes in which pyridine, absolute ethanol and distilled water were used as reaction medium respectively. The XRD and TEM have been applied to analyze the samples, and the grain sizes have also been calculated by Scherrer Equation. The results showed that in these experiments, all of the reaction products’ purity, crystallization, grain size and tropism increased with dielectric constant and polarity of the solvent. A novel Bi2Te3 nanowires with several tens to a hundred nanometers diameter and up to more than ten microns length have been prepared when distilled water was used as reaction medium. 1. Introduction The bismuth telluride based alloys are known as one of the best thermoelectric materials currently available near room temperature, their highest figure of merit ΖΤ≥1, and most modern thermoelectric coolers, thermal sensors, and so on, were made from such materials [1,2,3]. Traditional preparation method of Bi2Te3 is to melt the metal elements together [4,5], but this process requires an elevated temperature and a special protection against oxidation, and the product is always coarse-grained, which is adverse to decrease the thermal conductivity of the material. Mechanical alloying (MA) technique is another effective method to process bismuth telluride based alloys. In such process, solid-state reaction carried out through high-energy ball milling or attrition [6,7]. But this method needs a long duration and has strict requirement on raw materials. Hence, to develop a new processing approach of low temperature, low energy, short duration and high efficiency is one of the main goals of bismuth telluride based alloys research. Solvothermal syntheses are novel methods to prepare nanometer materials. They mean reactions take place under a certain temperature and pressure in an airtight system, in which water or organic solvent was used as reaction medium, and the product is not easy forming under common conditions. When react in such special system, the reactants can dissolve, diffuse and transform more easily. These methods have many advantages such as low temperature, short duration and the products’ high purity and fine-grained (always nanoparticles), hence become one kind of efficient synthesis approaches in inorganic chemistry and materials chemistry. There has been researchers synthesized Bi2Te3 compounds in N, N-dimethylformamide (DMF) [8,9]. In this study, pyridine, absolute ethanol and distilled water have been used as
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reaction mediums respectively to obtain Bi2Te3 nanocrystalline powders via solvothermal preparations under uniform route. The influences of different reaction medium on the products’ components, morphology and grain sizes have been researched, and
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