Effects Of Rare-earth Substitution On The Microstructure And Critical Current Characteristics Of Zr:REBCO Thin Films

The second-generation high-temperature superconducting tapes,rare earth barium copper oxide(REBCO),has its excellent current-carrying capacity and has great application potential in the entire temperature range of 4 to 77 K.However,REBCO tapes have the disadvantage of rapid attenuation of critical current in a strong magnetic field.It restricts its further wide application.The replacement of rare earth elements and the introduction of second-phase nanocolumns have been proven to effectively improve the magnetic field performance of the film.Previously,we have systematically studied the superconductivity of REBCO films substituted by different rare earth elements under different application temperatures and magnetic fields.However,there is still a lack of systematic research on Zr:REBCO films substituted by different rare earth elements.Therefore,this paper studies the influence of rare earth element substitution on the superconducting properties of Zr:REBCO thin films in a wide range.In this paper,a roll-to-roll MOCVD dynamic deposition system is used to optimize the deposition rate of Zr:REBCO film and adjust the content of rare earths in order to find the best process conditions:1)The best deposition rate is 0.09 μm/min,that is,the chemical source concentration is 0.075 mol/L,and the transport speed is 3 cm/min.2)When the rare earth content is 1.2,it is the best rare earth content of the Zr:EuBCO film.Excessive rare earth elements are easy to exist in RE211 phase,which increases the surface roughness of the film and reduces the film Jc.After exploring the best process conditions for different rare earth element Zr:REBCO films,XRD and SEM methods were used to characterize the microstructure of the film,and the four-lead method was used to measure the Ic under different temperatures and magnetic fields to study the effect of rare earth element substitution on Zr:REBCO films.The main conclusions are as follows:(1)The surface of the thin film with a larger rare earth ion radius is less impurity and is more flat,due to its higher optimal deposition temperature.(2)In the film with a large rare earth ion radius,the excessive rare earth element is more likely to form the RE211 phase,while in the film with a smaller rare earth ion radius,the excessive RE mainly exists in the form of RE2O3.(3)Under the conditions of 77 K zero field and 1 T,the large rare earth ion radius Zr:EuBCO film has excellent performance;when the temperature is 50 K～65 K,the Zr:GdYBCO film exhibits better performance,while the large rare earth ion radius Zr:EuBCO And Zr:GdEuBCO film performance decreases;when the temperature reaches 40 K,when the magnetic field strength is 3 T and 5 T,the small rare earth ion radius Zr:GdYbBCO film has a significant overall advantage in the whole angle range.(4)At the same temperature,the magnetic field increases,and the c-axis peak of the Zr:REBCO film gradually decreases.This is because the magnetic flux pinning center density introduced by 5 mol.%Zr doping best matches the 1 T magnetic field,and a higher magnetic field is required A greater amount of doping.(5)When the temperature drops to 50 K and below,the magnetic field increases,and the Zr:GdYbBCO film still has an obvious c-axis peak.This is due to the second phase growing along the c-axis introduced by the film itself,which acts as a good magnetic flux Pinning effect.The FP_B∥c and FP_min values of the large rare earth ion radius Zr:EuBCO film in this temperature zone are both low,indicating that the film lacks the effective pinning center of the ab plane and the c-axis to a certain extent.