| As the second-generation YB2Cu3O7-x(YBCO)high-temperature superconducting tape has high irreversible field,high current carrying capacity,critical temperature above liquid nitrogen temperature(?77 k)and relatively low production cost,it has a broad prospect in the application of high-field superconducting magnets.However,there are still many restrictions on the realization of the superconducting joints for YBCO coated conductor at home and abroad,so the second-generation HTS tape has been unable to be used in the closed-loop persistent current mode operation(PCM).Since the realization of the joint is related to the direct melting connection of the superconducting layer,this dissertation is dedicated to the preparation of YBCO superconducting film by metal organic chemical vapor deposition(MOCVD)and then study the melting behavior of the film.The deatails are as the following:1.Based on two kinds of heating electrode devices,a new home-designed heating electrode was optimized to solve the "arch bridge" phenomenon,which occurs when old electrodes are used to prepare wide tapes.The optimized electrode was used to prepare YBCO superconducting tape in MOCVD system,and the influence of heating current on the quality of YBCO film was studied.And the transverse uniformity of the film prepared by the optimized electrode was also studied.The results showed that the YBCO thin films grown at a heating current of 25.80 A had the best microstructure and morphology,and the critical current density(Jc)reached the maximum,which was 2.0 MA/cm2.In terms of lateral uniformity,the difference in out-of-plane texture(??)and the in-plane texture(??)yield full width at half maximum(FWHM)values in the transverse direction of the thin film which was prepared by the optimization heating electrode has shown less than 0.5 °and 0.9 °,the difference in Jc across the film is 0.2 MA/cm2.The results show that the microstructure and properties of the film are uniform.2.In order to control the melting behavior of YBCO films,the effects of different heat treatment parameters on morphology,microstructure and performance of YBCO films had been studied.The results showed that the morphology and microstructure of the film had been changed little only when the film is subjected to rapid heat treatment and the heating current density is from 3.46 A/mm to 3.62 A/mm,by the annealing treatment,the film Jc was restored to be consistent with the original value when the film thickness was 75 ?m.After analysis,it is found that the retention of Y123 phase in molten or semi-molten YBCO films is closely related to the recovery of superconductivity after annealing3.The influence of oxygen annealing time after heat treatment on the recovery degree of thin film superconductivity was studied.The results show that the annealing time within 4 hours after annealing is positively correlated with the recovery of thin film superconductivity.When the heating time is 4 hours,the recovery degree of superconductivity for the film was 70.36%.However,the recovery of the electrical properties of the films was not significantly improved by adding annealing time after 4 hours.4.The preparation method of the superconducting joint for YBCO tape was explored,and a self-designed device solved the requirement of both pressure and heating rate in the preparation of the joint,and improved the lap joint mode of the joint by using a laser drilling film to press on the joint. |
PDF Full Text Request