Study On Controllable Synthesis And Properties Of Bismuth Dibutide And Antimony

Bismuth telluride (Bi2Te3) and its alloys with Sb, Se, and so on are important thermoelectric (TE) materials and have attracted substantial interest from the research communities. In recent years, this semiconductor material has attracted great attention as a three-dimensional topological insulator, which is characteristic of a combination of an insulating bulk and conducting surface states of mass less Dirac fermions. More attentions were focused on the synthesis of Bi2Te3nanoplates because of excellent physical property. It has also been demonstrated by experimental results that the nanoscale thermo electrical materials revealed the impressive ZT compared to that of the bulk. The main approach to obtain high ZT materials was controllable synthesis of nano scale thermo electrical materials with optimal composition and structure. Based on this discussion, our work focused on the synthesis of Bi2Te3and Sb2Te3nano structures with a controlled growth space and morphology for application of TE and topological insulator。In chapter1, after a short introduction of the theory and research Progresses of TE materials and topology insulator as well as the Potential applications, We introduced several main approaches to obtain nano materials such as chemical vapor deposition method, hydrothermal method and electro-deposition&template method. Considering of the advantages of reaction processes for morphology control, we gave a short summary and design our experiments.In chapter2, we synthesized Sn doped Bi2Te3nanowires with a controllable aspect. Rhombohedra Bi2Te3nanowires with sub-100nm diameters were synthesized through Au-Sn co-catalyzed chemical vapor deposition under higher pressure (70KPa). These Bi2Te3nanowires were single crystals with a hexagonal lattice. The Sn catalyst played a key role in achieving the one dimensional nanowire structures. Under a lower reaction pressure (3Kpa) and without any catalyst, other morphologies were facilely obtained such as nanoplates, nanobelts and nanocrystals. Raman spectra revealed that compared to the Bi2Te3bulk material, the Bi2Te3nanowires displayed an Alu spectral peak, implying the breaking of symmetry. The temperature-dependent electrical measurement indicated that these Sn-doped Bi2Te3nanowires were metallic, with a high conductivity of1.6×105S/m-1at300K, higher than that of bulk B2Te3material.In chapter3, we introduced a two-step synthesized Te-Bi2Te3herterostructures by a rational solutioan-phase reaction. The process involved the nucleation of Bi atoms reduced from BiNO3on the surface of Te nanotubes, which served as sacrificial templates. The herterostructures synthesized in this study had a lengthof2-4um, which was the same length as that of the Te nanotubes, and a diameter of200nm, which was greater than that of the Te nanowires. The morphologies of Bi2Te3were strongly dependent on the concentration of the reducing agent. Using different concentration of N2H2.H2O, a series of Te-Bi2Te3heterastructures with different morphologies were obtained.In chapter4, we synthesized hexagonal nanosheets of antimony telluride single crystals by solvothermal method at200℃. In this solvothermal process polyvinyl pyrrolidone (PVP) was used as surfactant. SEM, TEM, HRTEM, SAED, XRD were employed to characterize the products. The reaction factors have been optimized for morphology control such as temperature, solvent, reducing agent, and surfactants. The reaction temperature and solvent played important roles in the formation of Sb2Te3single crystals, and the morphology of the products can be greatly influenced by the added surfactants and reducing agent.In chapter5, we summanied our work and introduced a short view about next research.