Effects Of Gd/Yb And Rare Earth Content On Structural And Electric Properties Of GdYbBCO Thin Films

REBCO high temperature superconducting thin films have always been the focus of research in the field of superconductivity because of their high critical transition temperature,high current carrying capacity and high irreversible field.In the past work,we systematically studied the superconducting properties of various rare earth and rare earth REBCO films in(10?77K,0?5T)environment.It was found that in low temperature and high field environment,GdYbBCO film has superior superconducting properties compared to other REBCO films.Both domestic and foreign research results show that both rare earth content and rare earth type will significantly affect the performance of REBCO film under 77 K and magnetic field.Therefore,this thesis carried out research optimization of superconducting properties of MOCVD-GdYbBCO films.First of all,we carried out the debugging and process optimization of the MOCVD system.The main purpose of the MOCVD system is to debug the optimal state and find the best process conditions:1)Increasing the density distribution of the spray holes and arranging the spray holes can form a good jetting effect while effectively suppressing heat convection.2)The optimum transport speed is 5 cm/min.3)The optimum chemical source concentration is 0.125 mol/L.4)The optimum spray spacing is 45mm.5)The optimum tension range is 0.2?0.3N.Under the premise of good MOCVD system,the effects of Gd/Yb and rare earth content on the properties and microstructure of GdYbBCO films were studied.The superconducting properties of GdYbBCO films with different Gd/Yb and rare earth contents were compared in(40?77K)and(0?5T)environments.The composition,surface morphology and phase of the films were analyzed by means of SEM and XRD.The composition was systematically characterized.The effects of different Gd/Yb and rare earth contents on the properties of GdYbBCO films were summarized,and the magnetic flux pinning mechanism of GdYbBCO films at low temperature was discussed.According to the effect of different Gd/Yb and rare earth content on the properties of GdYbBCO film,the main conclusions are as follows:1)Under the zero field condition,the best rare earth content of all samples is 1.3.The best Jc performance is GdBCO film and The YbBCO series film Jc has the worst performance.With the decrease of temperature,the performance of GdYbBCO(Gd/Yb=1)series film Jc gradually increases,and the full anti-over is achieved at 40K,while the performance of GdBCO series film Jc is gradually decreasing.2)Under the condition of(77K,1T),the properties of Gd1.2BCO and Gd1.3BCO films are the best,and the properties of Yb1.1BCO and Yb1.2BCO films are the worst.All films have no significantly enhanced magnetic properties in the c-axis direction through pinning phenomenon.3)At B//c,the performance of Gd0.65Yb0.65BCO film is optimal under the condition of(65K?40K,1?5T)and a significant strengthening peak appears in the c-axis direction.The c-axis peak at 3T is the most significant,and the peak intensity at 1T and 5T is weak.5)XRD phase and SEM morphology analysis can prove that the increase of rare earth content and Gd element will inhibit the formation of Ba-Cu-O phase.At the same time,when there are many Yb elements,the excess rare earth in the film mainly exists in the form of RE2O3 phase.With the increase of Gd element,the formation of RE2O3 phase is inhibited,and the excess rare earth mainly exists in the form of RE211 phase and solid solution.6)The presence of RE2O3 phase,Ba-Cu-O phase and RE211 phase in Gd0.65Yb0.65BCO film,but the magnetic flux pinning effect of Ba-Cu-O phase in c-axis direction is the main reason for the performance advantage of Gd0.65Yb0.65BCO film Jc_B//c.When the Ba-Cu-O phase is 65K or less,it gradually transforms into the dominant pinning center.