Research On High-performance Single-domain GdBCO High-temperature Superconducting Bulk Materials

High temperature superconductor(HTS),which had been discovered in 1987,has been became one of the international hotspots and impotent research contents all over the world.Because of the high critical temperature(Tc>90K),strong trapped flux density(YBCO:Btr=17.24T,29K;GdBCO:Btr=17.6T,26K),large magnet levitation force(the REBCO(RE= Y,Gd,Sm)samples fabricated by ourselves,the density of the levitation force is up to 10N/cm2 at 77 K)and stable suspension characteristics,the single domain REBCO(RE= Y,Gd,Sm,Nd,et.al)superconductors have the widely and potential applications in the high-tech fields,such as micro-magnets,superconducting maglev train,superconducting motor and superconducting magnetic separation system.In this paper,the low-cost fabrication,superconducting properties and the recycling growth process of the single domain GdBCO bulk superconductors have been investigated in details.The main work consists of four parts:(1)the single domain GdBCO bulk superconductors have been successfully fabricated by the conventional top seeded infiltration growth(TSIG)and modified TSIG process respectively,and the macrostructure,microstructure,levitation force(FL),trapped field(Btr),critical temperature(Tc)and critical current density(Jc)have been further investigated.(2)Through an assembly way to add the transition melt texture(TMT)layer between the NdBCO crystal seed and the solid phase layer,the nuclear phenomena caused by the defect of seed crystal can be inhibited efficiently during the growth processing,and the pure c-axis growth single domain GdBCO bulk superconductor was successfully prepared by changing the shape of the TMT layer,and the properties of this bulk was analyzed in details.(3)Study on the components of the solid solution induced by the Gd/Ba substitution in the GdBCO growth process,and the effect of the different ratio of BaO particles doping on the single domain GdBCO bulk superconductor was also investigated.(4)The failed GdBCO bulks were re-fabricated,and a simple method to recycle the waste REBCO bulks was proposed in this paper.The main results are summarized as followings:(1)The low-cost fabrication techniques including the modified top seeded melt texture growth(TSMTG)and TSIG processes were introduced in details.The results showed that the top seeded metallic oxide melt growth(TS-MOMG)process can be used to fabricate the single domain GdBCO bulk superconductors which just need three kinds of metallic oxide(Gd2O3,BaO and CuO)without preparing any other precursor powders.This new method can not only save the manpower,material resources,preparation cost,and also improve the efficiency of the preparation of single domain GdBCO bulk superconductor.The effect of the key technique parameters(including the melt growth temperature and the slow-cooling ratio)on the single domain GdBCO bulk have been optimized by the modified TSIG process,and the conventional solid phase powder(Gd211)was replaced by the new solid phase(Gd2O3+BaCuO2)for simplifying the fabrication processing.(2)The two different kinds of solid phase sources have been developed for fabricating the single domain GdBCO bulk superconductor by the modified TSIG process.After detailed investigations into the reaction of the solid phase,morphology,microstructure and superconducting properties of the as-grown samples,it can be concluded that it is helpful for us to obtain the high performance single-domain GdBCO bulk superconductor with the mixing powder of Gd2O3+BaCuO2 as the solid phase.Also,at the same time,using the NSPs can greatly simplify the working process,improve the working efficiency and reduce the cost of the fabrication and experimental time of the single-domain GdBCO bulk superconductors because only one powder BaCuO2 must be prepared in-home.The results are very helpful in enabling us to fabricate high-quality single-domain GdBCO bulk superconductor.(3)High performance and large single domain GdBCO bulk superconductors have been successfully fabricated by the TSMT-IG process.The effect of the growth morphology,growth interface,the magnetic levitation force and trapped flux of single domain GdBCO bulk superconductors has been investigated.The above result indicates that,the utilization of NdBCO seed crystal and the production efficiency of the single domain GdBCO bulk superconductor can be effectively improved by the new TSMT-IG process,which can inhibit the random nucleation phenomenon at some extent during the process of crystal growth.In addition,the application of new technology also helps to improve the growth performance of GdBCO samples.(4)Based on the TSMT-IG process,the processing technique of pure c-axis GdBCO bulk superconductor was proposed.It was found that a proper sized TMT doping can fabricate the well texture c-axis GdBCO bulk superconductor successfully,which provides a new idea for improving the bulk'structure.(5)The different ratio of BaO particles were doped to inhibit the the Gd/Ba substitution during the growth process by the modified TSIG method.It is investigated that the single domain GdBCO bulk superconductors can be successfully fabricated by doping the BaO particles between 0.5 wt%and 4 wt%,and superconducting properties including the levitation force,trapped field and critical temperature can be improved efficiently.The results can be concluded that the proper doping ratio can control the elements substitution effectively,and the solid solution phase can be greatly reduced at some extent.(6)Based on the fabrication process of different ratio BaO doping,a solid phase pellet with the concentration gradient was designed,and the large size GdBCO bulk superconductor with the temperature gradient in the radial direction was artificially prepared for the first time.In addition,the levitation force was analyzed in details.(7)A recycling processing technique for recovering the failed REBCO bulk was introduced in the last chapter.This new recycling method is very simple,and the success rate can up to 90%.The superconducting properties of recycling bulk can be compared with the single domain bulk.At the same time,the recycling process reduced the preparation cost of REBCO bulk superconductor at the maximum extent,which has the significant influence to the development of application of high temperature superconductor REBCO in the future.