Epitaxial Growth And Superconducting Properties Of Co³⁺ Doped GdBa₂Cu₃O_7-? Thin Films By Fluorine-free PA-MOD Method

REBa₂Cu₃O_7-??REBCO?superconducting coated conductors,such as YBCO and GdBCO,have achieved numerous attention because of their wide application prospects in the fields of biomedicine,transportation,electric energy,information and communication,aerospace and national defense security.However,preparation cost,efficiency and superconductivity are still the main factors that restrict the large-scale application of coated conductors.In this paper,high quality GdBCO superconducting thin films were prepared by adding Co³⁺into GdBCO precursor solution by self-developed fluorine-free polymer assisted metal organic deposition?FF-PA-MOD?method.In this paper,a self-developed fluorine-free polymer-assisted metal organic deposition?FF-PA-MOD?method was used to prepare high-quality GdBCO superconducting films with Co³⁺was doped in GdBCO precursor solution.Firstly,the effects of different Co³⁺doping amounts on the crystal structure,surface morphology and superconductivity of GdBCO thin films were studied.The research shows that the lattice constant of GdBCO?00l?decreases gradually with the increase of the doping amount of Co³⁺,and the superconductivity?J_c?increases first and then decreases,the best J_c value?3.5 MA/cm²,77 K,0 T?is found when the doping amount of Co³⁺is 0.001(GdBa₂Cu_3-xO_7-?,x=0.001).According to the analysis,this is due to the fact that Co³⁺doping?0.001?improves the flatness and compactness of the film.Secondly,the influence of sintering temperature on c-axis texture,surface microstructure and critical current density J_c?77 K,0 T?of pure and doped samples?Co-0.001?were systematically studied.And the mechanism of low temperature epitaxial growth induced by doping was revealed.The results show that Co³⁺doping significantly reduces the epitaxial sintering temperature of GdBCO films,expands the temperature window of c-axis nucleation of the films,and increases the J_c?77 K,0 T?of the films at the same sintering temperature,which may be because dilute Co³⁺doping reduced the temperature of“BaCO₃ to Ba_xCu_yO_z transformation”and“Ba_xCu_yO_z to GdBCO superconducting phase transformation”.Finally,the GdBCO superconducting films having a J_c value of 4.5 MA/cm²?77 K,0 T?and 1.5 MA/cm²?77 K,0 T?was obtained at a sintering temperature of 820°C and 760°C,respectively.Finally,the effects of sintering time on c-axis texture,surface microstructure and J_c?77K,0 T?of pure and doped samples?Co-0.001?were investigated.The results show that Co³⁺doped GdBCO superconducting films with J_c values of 4 MA/cm²?77 K,0 T?and 2 MA/cm²?77 K,0 T?can be obtained in sintering time of 30 min and 20 min respectively.Compared with the traditional fluorine-free method,the epitaxial growth time of GdBCO thin films was shortened by at least 2/3 by Co³⁺doping,achieving fast texture growth of high-quality GdBCO superconducting films.In this paper,the research results are beneficial to further improve the preparation efficiency and reduce the preparation cost of high quality REBCO superconducting thin films,and provide scientific basis for the large-scale application of REBCO coated conductors.