Fabrication And Elments Doping Study Of REBCO Films By Fluorite-Free MOD Method

In this thesis, the development, application and classification of superconducting materials has been summarized. The development and fabrication methods of high temperature Coated Conductor and REBCO film has been introduced briefly. And the improved critical current density Jc of REBCO coated conductor by elements doping has been presented in detail.DyBa₂Cu₃O_7-x (DyBCO) films have been synthesized on single crystal substrates of LaAlO₃ (100) by using a fluorite-free MOD method. The optimal epitaxial growth temperature was 770℃, water vapor intruduced in the gas atmosphere during the film growth process was not propitious for epitaxial growth. And melt-partially mehod was proposed to optimize DyBCO film process. The phase composition, microstructures and the critical temperature of superconductivity (Tc) and the critical current density (Jc) of DyBCO films have been investigated by x-ray diffraction (XRD), scanning electron microscopy (SEM) and mmps method. The results showed that exhibited high c-axis orientation, smooth, dense and crack-free surface with 300nm of thickness. . High quality film has been obtained by this method with Tc = 92 K, Jc= 1.5 MA/cm² at 77 K and self-field.The effect of impurity doping on critical current densities of YBa₂Cu₃O_7-x (YBCO) film in high magnetic field was investigated by chemical doping. the study focus on the performance of YBCO doped with Zn,Ni and Fe substituting for the Cu site, which is YBa₂Cu_3-xM_xO_7-y(M=Zn,Ni,Fe), X=0.0005, 0.001,0.005. The results show that the excellent biaxial textures and improved density and smoothness of film surface for doped YBCO films . Impurity doping suppressed superconductivity ,which result in the degrade of Tc ,but pinning center were intruduced to improve Jc .the effect of flux pining varies with temperature ,magnetic and elments . Zn doped film with x=0.001 perform the best pining effect in 77K, and Ni with x=0.005 in 77K and 65K ,with x=0.001 in 50K,30K ;Fe doped film with x=0.001 perform the optimal flux pinning in high magnetic field.