Chemical Solution Deposition Prepared By Molybdenum Department Of Burning The Greenstone Type Buffer Layer

The second generation high temperature YBCO coated conductor, on comparision with the first genetation Bi-2223/Ag superconducting material, has higher critical current density in high magnetic field and is therefore an only selection for magnet preparation at liquid nitrogen temperature and possess bright prospects in industry. The architectures of coated conductor consist of four layers: metal substrate, buffer layers, superconducting layer and protecting layer. As buffer layers take on two major tasks of communicating the texture and taking chemical barrier, there are an important part of YBCO coated conductor accordingly.Preparation thechniques of buffer layers include both vacuum technology and non-vacuum technology. Chemical solution deposition method, a typal non-vacuum technology, is a high potential technique for large-scale industrial production since no expensive high-vacuum systems are used. In this thesis, three new films (Nd₂Mo₂O₇, Gd₂Mo₂O₇ and Sm₂Mo₂O₇) with pyrochlore structure have been prepared by CSD techinque. And their texture qulities and surface appearances were characterized by X-ray diffraction (XRD), atomic force microscope (AFM) and metallurgical microscopy. Then YBCO layers on YSZ/NMO structure were grown up by TFA-MOD method and valuated the quality of the buffer layers by testing the performance of YBCO layers. In addition, a primary investigation on tungsten-based double-perovskite buffer layer has also been taken. Detailed contents of this thesisis are listed as follows:1. Molybdenum (Ⅳ) dioxo acetylacetonate MoO₂(acac)₂ and neodymium (Ⅲ) acetylacetonate Nd(acac)₃ were selected as precursor materials and dissolved in methanol and propionic acid to obtain the optimal precursor solution for preparation of Nd₂Mo₂O₇ film by CSD method. The precursor solution was then spin-coated onto single crystal YSZ substrate or Ni-W substrate. The optimal process for the Nd₂Mo₂O₇ buffer layer with good c-axis texture on YSZ substrates in Ar are: pyrolysis of the wet film at 550℃for 1 h and then crystallization at 1000℃for 2 h, with total cation concentration of 0.2 M. Similarly, the optimal process for Ni-W/NMO in Ar-H₂ are: pyrolysis of the wet film at 350℃for 1 h and then crystallization at 1000℃for 2 h, with total cation concentration of 0.2 M.. 2. For the preparation of Sm₂Mo₂O₇ buffer layer, molybdenum (Ⅳ) dioxo acetylacetonateMoO₂(acac)₂ and samarium nitrate Sm(NO₃)₃ were screened as optimal precursors and dissolved in ethanol to get precursor solution. Similarly, molybdenum (Ⅳ) dioxo acetylaceton(?)te MoO₂(acac)₂ and gadolinium (Ⅲ) acetate hydrate Gd(OOCCH₃)₃·4H₂O) were optimal precursors and dissolved in methanol and propionic acid as optimal precursor solution for the preparation of Gd₂Mo₂O₇ film. The optimal processes for the preparation of YSZ/SMO or YSZ/GMO architectures in Ar are same: pyrolysis of the wet film at 550℃for 1 h and then crystallization at 1000℃for 2 h. But in Ar-H₂ atmosphre the crystallization temperature for SMO decrease to 900℃.3. The preparation of YBCO layer on YSZ/NMO architechture by conventional TFA-MOD method was performed and found that YBCO layer has good c-axis texture with the surface being dense, smooth, and crack-free. The transition temperatur and critical current density of the as-prepared YSZ/NMO/YBCO architecture are 90 K and 1.8 MA/cm², respectively, which indicated that the NMO film maybe a potential buffer layer for YBCO coated conductor.4. Double-perovskite Sr₂CuWO₆ powder was prepared by solid state reaction. The optimal heat-treament process to get Sr₂CuWO₆ powder with minimum impurity is two steps: heat-treament at 1200℃for 10 min and then quenching to room temperature. Moreover, several tungsten-based double perovskite precursors, with good solubility, high stability and satisfactory wettability in common organic solvent, were synthesized.