Study Of YBCO Multilayers Fabricated Technology

The second-generation high-temperature superconducting YBa2Cu3O7-δ(YBCO)coated conductor has high current carrying capacity and high irreversible field,and can maintain high performance in the liquid nitrogen temperature zone,making it the most potential high-temperature superconducting material.The coated conductor is composed of texture template,buffer layer,superconducting layer and protective layer,and the superconducting layer,which carries current,is the core component.The metal organic deposition technology(MOD)for the preparation of superconducting layer has the advantages of easy adjustment of metal ion ratio,easy introduction of artificial pinning center and low cost,and is one of the hotspots in the field of superconductivity.In this thesis,YBCO multilayer films were prepared by metal organic deposition technique.The preparation process of YBCO thick film was optimized,the element diffusion process of low-fluorine/fluorine-free double-layer film was studied,and YBCO composite superconducting film was prepared.The main research contents are as follows:The thickness of the single layer YBCO is improved by adjusting the concentration of the low-fluorine precursor.The thickness of the YBCO can be further increased by increasing the number of coatings and pyrolysis.It is found that the thickness has an important influence on the epitaxial growth and critical current density of YBCO.When the thickness of YBCO exceeds the critical thickness,the orientation of the superconducting layer deteriorated and the performance decreased remarkably.The results show that the YBCO superconducting layer with excellent performance can be obtained with low-fluorine metal organic deposition process at thickness 1.1 μm,and Jc reaches 2-3 MA/cm2@77 K self-field.The YBCO-LF/YBCO-FF bilayer film was successfully prepared by combining low-fluorine metal organic deposition with fluorine-free metal organic deposition.Compared with the traditional fluorine-free precursor film,the double-layer precursor film has good microstructure and surface morphology.During the pyrolysis treatment of the double-layer film,the upper layer F element diffuses to the lower layer,and the lower layer C element decreases.This diffusion process facilitates YBCO to achieve good c-axis orientation and sharp in-plane and out-plane texture,as well as excellent performance.The FWHM of the YBCO(005)peak is 0.9°,the in-plane scanning FWHM of the YBCO(103)peak is 1.47°,and the critical current density of the sample at 77 K is 3.9 MA/cm2.YBCO+5%BHO/YGdBCO bilayer film was prepared by low-fluorine metal organic deposition and pulsed laser deposition.By controlling the thickness,a 300 nm-YBCO+5%BHO/100 nm-YGdBCO bilayer film with good properties was prepared.The in-plane scanning of the composite film has a FWHM of 1.59°,an out-plane scanning FWHM is 0.52°,with a sharp texture,and the Jc reaches 2.11 MA/cm2 at 77 K.