Prepare Epitaixial DBCO Film By Flourinate-Free MOD Method And Develop The Epitaxial Process

The aim of this thesis is to prepare epitaxial DBCO films using fluorinate-free MOD, design appropriate epitaxial growth processing route and study the composition influence on the microstructure and superconductivity of epitaxial DBCO films. To prepare epitaxial DBCO films by fluorinate-free MOD method, three various solutions, a(solutes: Dy(HCOO)₃. xH₂O, Ba(HCOO)₂. xH₂O, Cu(HCOO)₂. xH₂O, solvents: distilled water and formic acid), b( solutes: Dy(CH₃COO)₃. xH₂O, Ba(CH₃COO)₂. xH₂O, Cu(CH₃OO)₂. xH₂O, solvents: distilled water and acetic acid, additive: PVA), c(solutes: Dy(CH₃COO)₃. xH₂O, Ba(CH₃COO)₂. xH₂O, Cu(CH₃OO)₂. xH₂O, solvents: pure propionic acid, additive: PVB) were used as precursor solutions. Compared with the stability of these solutions, it was found that a and c solutions were more stable than b. After being spin-coated, a, b, c coated films named according to coating solutions, were pyrolyzed and measured using SEM. It was observed that the morphology of the film c was smoother and denser than others. According to the stability of a, b, c solutions and the morphology of a, b, c pyrolyzed films, it was known that c solution was the most suitable solution for fluorinate-free MOD method precursor to prepare epitaxial DBCO films and the pyrolyzed processing route was developed for c coated films.In order to find the appropriate temperature range for epitaxial growth of DBCO films, the pyrolyzed films were sintered at various temperature, 730℃, 740℃, 750℃, 760℃, 765℃, 770℃, 780℃. Phase composition and texture of sintered films was investigated by XRD. The microstructure and morphology of sintered films was studied using SEM. From the measurement results, the suitable epitaxial growing temperature range from 760℃to 770℃was found. Then the sintering process was designed for expitaxial growth of DBCO films, which was improved successful by the good c axial texture and smooth, dense morphology of sintered DBCO films.The effect of composition on the microstructure and superconductivity of epitaxial DBCO films was studied that the Cu composition ranging from 3.0 to 3.57 did not have any significant influence on superconductivity of epitaxial DBCO films, but the Ba compositition ranging form 1.9 to 1.7 made a seriouseffect on the microstructure and superconductivity of DBCO films. It was foundthat the sample with the ratio of Dy: Ba: Cu=1: 1.8: 3.3 had the sharpestsuperconducting transition and highest J_c (77K, 0Oe)≈1.35×10⁶A/cm² in all ofsamples.