Chemical Solution Prepared By The Technical Study Of The Coated Conductor Buffer Layer

YBa₂Cu₃O_7-d (YBCO) coated conductor, on comparison with first generation high temperature superconducting material Bi-2223/Ag, have bright prospects in industry, due to its good performance of loading current in magnetic field at 77 K. Hence the preparation technology for low-cost, high-performance YBCO coated conductor becomes the research focus of the current high-temperature superconducting materials. As two major tasks of buffer layers for coated conductor is to communicate the texture and take chemical barrier, therefore, the properties of buffer layers have a direct impact on the superconducting properties of YBCO layer. So it is the key technology of coated conductor to choose and prepare low-cost and high-quality buffer layers.In recent years it was found that a compound with perovskite structure is an ideal buffer materials. Chemical solution deposition (CSD) is the most prospective techniques for industrialization in the preparation of the function layers, in the viewpoint of low-costs and large-scale. This thesis will discuss our studies on preparation of perovskite-type buffer layers by chemical solution deposition. Precursors and precursor solutions were analyzed by IR, TG-DSC and other analytical techniques. And then the grain orientation and surface appearances of the buffer layers were characterized by X-ray diffraction (XRD), atomic force microscope (AFM) and scanning electron microscopy (SEM). Finally the preparation conditions of the buffer layers were optimizedIn this thesis, two films (LaNiO₃ and NdGaO₃) with perovskite structure on YSZ single crystal substrate, which has smaller lattice mismatch with the perovskite (ABO₃) compounds, have been prepared. And the optimized buffer layers and preparation conditions were screening through a series of experiments and these will be a preparation for continuous process on long substrate. The optimized precursors were selected and dissolved in suitable organic solvents according to a certain molar ratio, to get stable precursors solutions with good wettability on a substance. The gel derived from the precursor solutions after evaporation of the solvents was studied to determine the range of heat-treated temperatures, and the precursor solutions were then spined on a single crystal substrate to form wet film, which was dried and decomposed to form buffer layer film through an appropriate heat-treated process.We found that the heat-treated process (high temperature and low temperature steps) plays an important role on the influences of the cubic texture and the surface roughness of buffer layers. At the same time we also found that the thickness of the LaNiO₃ film has a certain impact to its cubic texture and that the heat-treated time has influence on the cubic texture of NdGaO₃ film. It is concluded that for different buffer layer films different heat-treated process should be chosen. It is a trend that the higher the heat-treated temperature is, the bigger the grain is and the higher the final surface roughness of film is; and when the thickness of the film increased, the surface roughness increased, too. Then we studied the screening and preparation of organic-tungsten salts which could be used as precursors for two double-perovskite structure (Ca₂NiWO₆ and Ca₂CoWO₆) buffer layer films. And the phase compositions of their powders, which were derived from the gel pyrolyzed at different temperatures, have been investigated in order to make enough preparation for the optional heat treated process of double-perovskite buffer layers by chemical solution deposition.Through our study on the preparation process of perovskite buffer layers, we found that the optional thermal decomposition and crystallization temperature for the LaNiO₃ film with highly c-axis texture was 350 and 600℃, respectively. We found also that the texture is kept when its thickness reached up to 100 nm, surface roughness of the LaNiO₃ film was only 2 nm, and the film has shown good conductive properties derived from optimum conditions. The NdGaO₃ film with good c-axis texture was derived through anealing at 1000℃for three hours, and the film was crack-free with roughness of 5 nm.Also, we found that the preparation process for double perovskite compounds is greatly different from that of perovskite films, although there are some similiarities. It is found that there are large amount of impurity in the powder derived from Ca₂NiWO₆ and Ca₂CoWO₆ gel at different heat-treated temperatures, so it needs further study on the preparation of double-perovskite structure buffer layer by chemical solution deposition technique.