Rapid Preparation Of Ybco Superconducting Thin Films, Chemical Solution Method

During superconducting materials, YBa2Cu3O7-xYBCO) coating conductor is widely considered to be the most promising high temperature superconductor of the second generation for its unique properties. Many researchers study its scale production and applications for a couple of decades. The physical method and chemical method are two important approaches for the preparation technology of YBCO superconducting film. Chemical method is more relatively simple operation, low cost, and more easily opertaion to implement. In traditional TFA-MOD (Metal Organic Deposition using Trifluoroacetates), the long calcinations time of YBCO film leads to a low production and needs to be solved in order to carry out a fast long tape production. Therefore, we studied the fast preparation methods of preparing the YBCO superconducting film in this thesis.In TFA-MOD, we studied the influences of the water partial pressure on properties, such as precursor film morphologies, YBCO films microstructure and the performance of the YBCO film. It was found that the range of P (H2O) not only affected the film morphologies after calcinations, but also influenced morphology, structure and performance of YBCO films. If the P (H2O) was too large to be moisture absorption during the decomposition process, it caused partial shrinkage, deformation and cracking in film. If the P (H2O) was lower in the crystallization process, the YBCO nucleation didn't grow completely, thus the non-superconducting-intermediate phases and large pores appeared, which led to not only the reduction of a current path area, but also the concentration of an electric field. If the films were treated under higher P (H2O), small pores and cracking film are existed, which suggested to reduce Ic. It was found that the YBCO films with better morphologies, microstructure and Jc were attained in P (H2O) of 8%.It was an important direction of higher YBCO preparation rates to choose stabile Cu-salt without F instead of TFA-Cu precursor. We studied the influences of two different chelating agents on the appearance, structure and performance of YBCO film, by replacing TFA-Cu whith nitric copper nitrate added chelating agent consisting of polyethylene glycol (PEG) and sucrose. PEG can help to maintain solution uniformity during decomposition. On the other hand, a cross-linking reaction during sucrose caramelization made the film surface smoother and flatter. The new copper salt, that is, two kinds of chelating agent coordinates with the copper nitrate, decomposed faster, just only 80 min., and smaller sizes of the copper oxide particles after decomposition appeared, compared with a single chelating agent added. After the crystallization process at 760℃, 1h, the YBCO films after adding the sugar and PEG had a better characteristics, such as a low pore, no a-axis grains, stronger YBCO(00l) peak, non-superconducting phases and better superconducting properties.A polymer-assisted deposition (PAD) process developed in recent years is a new solution deposition technique of preparing film. Generaly, the precursors were resolved in aqueous solution. A precursor solution was prepared by dissolving nitrates of Y, Ba and Cu in aqueous solution with the chelating agent of sucrose, PEG and polyvinyl alcohol. The DSC/TG thermal analysis indicated the presence of polymers and nitrates in the precursor resulted in a suppression of the nitrate decomposition temperatures. After identifying the optimal process condition of O2 pressure, crystallization at 100ppmO2/N2 resulted in high-quality YBCO films with denser morphologies, high phase purity, stronger YBCO(00l) peak, Tc～91K and Jc～1MA/cm2(77K, OT).The improved precursor solution DEA/YBCO for preparing YBCO superconducting film showed rapid, simple and easy fabrication characteristics. DEA (Diethanolamine) not only chelates TFA-Cu resulted in avoilding sublimation of Cu-TFA, but also prevents film buckling by relaxing stress gradients and make film stable. The as-deposited films pyrolyzed at 325℃in air for 90s showed smooth surface morphologies, and then, the YBCO film with preferable density and performance after crystallization temperature of 800℃,60min, was successfully obtained. This YBCO solution deposition method provides an experimental basis for production of commercializable coated conductor wires.Crystallization one-step via a diethanolamine-modified trifluoroacetic precursor solution was a simple process for solution deposition method of YBCO superconducting film. Because the time of low temperature decomposition was relatively short, we can compensate for the process of the low temperature decomposition through high temperature process before 400℃at slow heating and low oxygen atmosphere. It was found that DEA appeared to extend the thermal decomposition range of the -Cu-DEA-Cu- molecular polymer chain and prevented Cu-TFA from sublimating through the DSC/TG analysis. The YBCO precursor solution was improved by DEA, which made the preparation time shorten 10h and above at least, and the YBCO superconducting film prepared by water gas at 350℃, the crystallization at 820℃for 60 min exhibted good performance. The crystallization one-step for preparation is the advantage of simple process, easier control parameters and shortened preparation time, and is helpful for fabrication of long-length YBCO tapes with high performance using the reel-to-reel system.