Study On Electromagnetic Fields Characteristics And Micro-structural Mechanism Of REBCO Thin Film

After more than 20 years of in-depth global research,REBa2Cu3O7-?(REBCO or RE-123,where RE=rare earth)thin film superconducting tape with high current carrying capacity and mechanical strength has been initially commercialized.However,their cost/performance ratio is still unsatisfactory,especially in high magnetic fields.Therefore,various methods have been studied at home and abroad to further increase its self-field and in-field critical current(Ic),including rare earth substitution and its combination,or the addition of BaZrO3,BaSnO3 nanoprecipitates to enhance the field critical current,so this article will study the properties of different RE elements replacing rare earth Y in the electromagnetic field and analyze and explain from the microstructure.First of all,we carried out the debugging and process optimization of the MOCVD system.Its main purpose is to debug the MOCVD system to the best state and find out the best process conditions;under the condition that the MOCVD system is in good condition,a variety of REBCO films are prepared;Comparing the superconducting performance of different REBCO films in the environment of(20?77 K,0?5 T),using scanning electronmicroscope,XRD,TEM and other analytical methods to systematically characterize the film composition,surface morphology,phase composition,etc.In summary,the influence of different RE elements on the performance of REBCO film is summarized,and the magnetic pinning mechanism of REBCO film at low temperature is discussed.According to the research on the influence of different RE on the performance of REBCO thin films,the following conclusions are mainly drawn:1)The small rare earth ion radius film Jc increases significantly as the temperature decreases,while the large rare earth ion radius film Jc increases slowly;2)The different rare earth ion size Jc(T)The curves have obvious intersection;3)Jc(T)under a fixed magnetic field can be fitted to Jc?(1-T/Tc)m(1+T/Tc)2,the index m of the small rare earth ion film Larger,which means that the diameter of the nanoprecipitates contained in the thin rare-earth ion radius film is greater than 2 Cab at low temperature,thus causing the intersection of the Jc(T)curve.4)We carried out the experiment based on the core pinning force Reasonable interpretation of several magnetic flux pinning models 5)The superiority of the small ion radius film at low temperature is analyzed from the microstructure.The GdYb123 film not only forms RE2O3 along the ab plane,but also forms on the c axis The phase becomes an effective pinning center at 65?30 K.When the temperature is less than 20 K,a large number of small-scale weak pinning defects,including 0D point defects,3D spherical defects,and large density strain fields generated between the second phase and the matrix phase The defects can be transformed into effective pinning centers,and the pinning force behavior has changed from a single pinning at a high temperature of 77 K to a small group pinning at a low temperature.