Fabrication Of GdBCO Films By Fluorite-Free MOD Method Study

In this thesis,the development,application and classification of superconducting materials were summarized.The development and fabrication methods of REBCO high temperature superconducting films were introduced.The structure,performance parameters and the epitaxial growth mechanism were presented with the research goal and content.GdBa₂Cu₃O_7-x(GdBCO)films have been synthesized on single crystal substrates of SrTiO₃(100)by using a fluorite-free MOD method.We have recently developed a fluorite-free MOD synthesis with several important advantages including precursor solution stability,improved film density,and elimination of HF during processing.The phase composition,microstructures and the critical temperature of superconductivity(T_c)and the critical current density(J_c) of GdBCO films have been investigated by x-ray diffraction(XRD),scanning electron microscopy(SEM)and four-probe method.The J_c value of the GdBCO film in self-field at 77 K was determined by the application of the Bean critical state model formula using the M-H curve.In this thesis,the decomposition procedure,the optimal crystallization temperature and oxygenation temperature were primaryly confirmed.The optimal melting temperature and time of the melt-epitaxial growth technics were clarified. The melt-epitaxial growth GdBCO films exhibited high c-axis orientation,smooth, dense and crack-free surface with 300nm of thickness.The T_c of GdBCO films was 90K and J_c reached 0.6 MA/cm² at 77K in the self-field.In the last part of the thesis,the epitaxy mechanism and the influence factors of the melt-epitaxial growth films were explored.