Study On Highly Superheated Thin Film With New Structure In Seeding The Epitaxial Growth Of REBCO High-temperature Bulk Superconductors

Because of the great superconducting properties and potentialperspective of applications, high temperature superconductors are widelystudied by scientists and even become technology of domesticallystrategic significance. REBa2Cu3O7(REBCO or RE123, RE=Y, Gd, Sm,RE refers to rare earth elements) bulk high-temperature superconductorsare of high trapped field and have a promising perspective of applications,such as magnetic bearings and flywheel energy storage devices. In orderto be used practically, REBCO bulk superconductors with highsuperconducting properties should be manufactured first. Many attemptshave been carried out for the growth of REBCO bulk materials, but thereare still several problems to be solved. Nowadays, YBCO bulksuperconductor can be obtained successfully, but the growth of LREBCO(LRE=Nd, Sm, Gd) bulk superconductors is still to be improved. On theother hand, the batch processing failure rate for REBCO bulks is about20%, which seriously limits the potential for industrial use. Those failedREBCO bulks, if recycled, still retain considerable value. In this work, using a special film seed with high thermal stability to get good epitaxialgrowth, we have been trying to grow high-property REBCO bulksuperconductors and recycle failed REBCO bulks in a simple and feasibleway. We have done some good jobs, and some main results in our workare listed as follows:1. Highly superheated thin film with new structure to seedhigh-property REBCO bulk superconductors in TSMTG.In the cold-seeding top-seeded melt-textured growth (TSMTG),YBCO-buffered NdBCO film, i.e., NdBCO/YBCO/MgO thin film is firstintroduced as a seed material. With the specialNdBCO-film/YBCO-buffer-layer/MgO-substrate structure,NdBCO/YBCO/MgO thin film has better thermal stability. In TSMTGheating process, NdBCO/YBCO/MgO thin film can endure a maximumprocessing temperature (Tmax) up to1120°C (world record), which isabout20°C higher than that of NdBCO/MgO film, showing greatthermal stability. Because NdBCO has the highest Tp(Tp≈1085°C)among the commonly applied REBCO materials, there is not a properseed material to induce its growth. But using this NdBCO/YBCO/MgOfilm as the seed, we are the first to obtain a NdBCO bulk superconductorwith a diameter of16mm in air, without any silver dopant to reduce theTp.2. Use of film seed with high thermal stability in recycling failed YBCO bulk superconductorsREBCO bulk high-temperature superconductors have a potentialperspective of application. However, because of the expensive materials,the cost of REBCO bulk production is rather high. On the other hand, thebatch processing failure rate for REBCO bulks can be as high as20%. Ifrecycled, those failed REBCO bulks, which usually contain expensive REmaterials and Pt or Ag addition, still retain considerable value. Using thehighly superheated NdBCO/YBCO/MgO film, which can endure a Tmaxabout100K higher than the Tpof REBCO (RE=Y), the failed REBCObulks could be easily decomposed and we succeeded in recycling thefailed REBCO bulks in a simple and feasible process. The recycledYBCO bulks have comparable superconducting properties to thenormally processed superconductor bulks. The recycling approachpresented in our work is simple, feasible and effective. It helps to protectenvironment and has a positive effect on cost reduction.Our work may provide some new ideas for the epitaxial growth ofhigh-property REBCO bulk superconductors, and present a simple andeffective way of recycling failed REBCO bulks.