Thickness Effect And Artificial Flux Pinning Properties Of Superconducting REBa₂Cu₃O_7-x Coated Conductors Derived By Metallorganic Solution Deposition

Since the discovery of high temperature oxide superconductor,Researchers are concerned by their ability to carry high current capacity for prospective application in electric power transmission systems.The second generation of REBa₂CuO7_-??REBCO,RE=Y,Gd,Dy etc rare earths?high temperature superconductor?HTS?coated conductors based on thin film technology,have involved much attention in recent years in worldwide.Significant progress has been focused on the improvement of high quality YBCO superconducting thick film YBCO superconducting thick film.Immense film thickness is desirable be achieved without degradation of the critical current density,an issue that is still under investigation in all the several deposition technologies.The implementation of low-cost deposition techniques for high critical current YBCO-coated conductors is one main objective to realize prevailing utilisation of superconductivity in power applications.Chemical solution deposition techniques appear to be a very promising route to realize this purpose.The use of trifluoroacetic?TFA?precursors has already been shown to be very competitive and has to be considered one of the most valuable alternatives for achieving low-cost chemically based coated conductors.Extensive progress has been made by many research groups in worldwide to improve the critical current density?J_c?in REBa₂Cu₃O_7-x-x coated conductors.The Superconducting materials increase performances of machines by intensively using in MRI,energy storage systems,generators,engines,cables,superconducting wires and tapes,accelerators,electromagnets,etc...In these applications,the?HTS?possess very high J_c values at low temperature even in high magnetic fields.Many kinds of crystalline defects,such as fine precipitates of non-superconducting phases,dislocations,vacancies,grain boundaries,and so on,are considered to act as pinning centers.However,the J_c values rapidly decrease with increasing temperature in magnetic field.The main reason of the J_c depression is the lack of effective pinning in the structure.Depending on these reason,a novel technology has been developed by means of a nanostructure engineering to create artificial pinning centers in HTC materials.With this regard,increasing critical current density and improvement of flux pinning properties of REBCO superconducting films with nanodots,or nanoparticles,as pinning centers are aimed.The strong increase of J_c can be achieved when the flux lines are pinned and their movement completely prevented.The flux lines could be pinned by incorporating effective artificial pinning centers leading to high current density at higher magnetic fields and higher temperatures.This paper aims at the improvement of thickness and field-performance of Y?Gd?BCO coated conductors on metallic substrate.Main research works and results are summarized as below.?1?An investigation on the growth of thick Y?Gd?BCO film on buffered metallic substrate are carried out by adjusting the chemical solutions with various approaches including the different contents of TFA-acid,as well as the different concentration of starting solution.The experimental results showed the existence of a maximum thickness for certain precursor solution.It is believed that an appropriate withdrawal speed based on the concentration of starting solution plays quite an important role in the preparation of thick REBa₂Cu₃O_7-xfilm with good superconducting properties. ?2?Artificial flux pinning?APCs?for REBa₂Cu₃O_7-xcoated conductors are studied,focusing on the incorporating of the second phase nanoparticles with different classification into REBa₂Cu₃O_7-x-x matrix to improve its performance in magnetic field.An approach is proposed based on the combination of one dimensional APCs?SrZrO₃ nanoparticles?with a three dimensional artificial ping center?Dy₂O₃nanoparticles?.High-quality Dy₂O₃ and SZO CO-doped single layer of YBCO films successfully grown using super low fluorine metalorganic deposition?SLF-MOD?,high critical current densities were achieved.The studied films exhibit a good microstructure consisting of pinning centers.The additions of 3%of SZO nanoparticles to the 50%Dy₂O₃,to leads to a smooth surface and well textured epitaxial YBCO films,increasing the self-field J_c and an additional enhancement on F_p?B?.A pinning force density of 15GN/m³ at 50 K at the field of 1.8 T was achieved.Despite the slightly decrease in T_c,J_c was well correlated with the magnetic field.Besides,the F_p,max?B//c?of nanoparticles at low temperatures is found to be much stronger than that of nanorods.In this work,the effective combination of the two types APCs is added into the YBCO films simultaneously,which makes a strong flux pinning and results in an overall enhancement on J_c and F_p in the magnetic fields. ?3?Another approach is proposed to build up the insertion of interlayer of SZO and BZO in the matrix of bilayered YDyBCO films by SLF-MOD with objectives of understanding the underlying mechanism of the T_c and J_c performance of YBCO films and the mechanism of superconducting property enhancement due to additional interlayer in the YBCO film.It is well known that J_c is closely related to the flux pinning,thus it is important to study some flux pinning in REBa₂Cu₃O_7-xfilms.The flux pinning mechanism is also addressed in this work,J?B?curves pinning advantage and the increased current densities resulting from the introducing of SZO are maintained regardless of the applied field ranging from B=0 to5 T and the temperature ranging from 50 K to 77 K?4?Third approach is proposed,being successful in the incorporating of three dimensional artificial pinning centres.The approach is based distributing a secondary phase in the film by modifying the solution composition to get a significant doping amount of a second face of Dy₂BaCu₁O₅ on the top layer of bilayered YDyBCO,the resultant film has hereto bilayered structures.That makes the technique potentially suitable for large-scale production of superconducting coated conductors.In addition,the thickness,of the films is relatively large?about 1?m?which would make them suitable for potential high power applications that require high critical currents.In general,the present paper is focusing on fundamental understanding of both the fabrication and characterization of REBa₂Cu₃O_7-xderived by low fluorine MOD,with emphasis on optimizing the second phase doping amount.The work is helpful for the achievement of good quality films,the effects of the doping amount in relation to microstructure,superconducting transition temperatures and critical current density.Extensive discussion is included on the flux pinning mechanism in films with different interlayers,using the scaling function of a modified Bean model.