Study On The Preparation Of Large-sized High-performance SmBa₂Cu₃O_7-? Bulks And High-thermal-stable NdBa₂Cu₃O_7-? Film-seed

High temperature superconductors(HTS)have attracted much attention due to their unique physical properties and wide application prospects.Possessing high trapped fields,REBa₂Cu₃O_7-?(REBCO or RE123,RE refers to rare earth elements such as Y,Sm,Gd and Nd)HTS have a promising perspective of applications,such as superconducting storage,magnetic bearings,magnetic transportation and so on.So far,YBCO system has been extensively studied and there are mature techniques in the batch growth of YBCO bulks.Compared to YBCO,Sm BCO superconductors possess higher T_c and J_c and have bright application prospects.But problems like serious Sm/Ba substitution and brittle nature within Sm BCO samples deteriorate their superconductivity.Additionally,high peritectic temperature of Sm BCO makes it hard to find a suitable seed for inducing their growth.All of these factors hinder the way of batch growth for large-sized and high-performance Sm BCO bulks.Therefore,finding a simple and reliable method to prepare desirable Sm BCO bulks in air and searching for high thermal stable seed materials are of great significance in promoting the industrial applications.In this thesis,the work mainly concentrates on two respects:For the purpose of inhibiting Sm/Ba substitution,macro segregation and Sm₂Ba Cu O₅(Sm211)coarsening,Ba-rich modified precursor powders composed by Sm₂O₃ plus Ba₃Cu₄O₇(BMPP)and layered Ba-rich modified precursor powders(LBMPP)without Sm211 additions were employed to fabricate Sm BCO bulks.Using BMPP method,a 24 mm-diamter Sm BCO single domain bulk with a levitation force of 51.5 N and a trapped filed of0.5374 T was successfully fabricated in air.The mechanism related to the enhanced properties for the BMPP bulk was clarified.The Sm211 particles of LBMPP processed bulk were effectively refined according to the observed microstructure by means of Optical Microscope and Scanning Electron Microscope.Refinement of RE211 is beneficial to improving superconductor performance.Therefore,it's reasonable to conclude that LBMPP samples may have higher performance.During the research,we found that the samples cracked frequently.After systematic experiments,we optimized the process and took measures like prolonging the holding time in the heating stage and giving up the bottom pellet for liquid source.Finally,we effectively reduced the cracks.Regarding the suitable seed,here,innovatively combining superheating nature of two dimensional REBCO thin films with doping effect,we report a novel film,Mg-doped Nd BCO/YBCO/Mg O thin film.Distinctively,the YBCO buffered Mg-Nd BCO film successfully endured a T_max of 1128oC(43oC above its T_p)and induced the growth of Sm BCO bulks as a seed material in TSMG.To our knowledge,it's the highest T_max of Nd BCO seed materials used in the cold-seeding TSMG method up to now.We show how the observed metastable phase is linked to the distinctive film architecture.The research work presented here has provided some new ideas for the development of large-sized REBCO bulk with high superconducting performance and the preparation of similar brittle functional oxide materials in the future.Additionally,some high-thermal-stability-required seeding technological applications,such as batch growth and failed bulk recycling,are likely to be realized by this novel Mg-doped Nd Ba₂Cu₃O_7-?film seed.Finally,we hope that the novel film can provide some enlightenment and reference for the research of other high thermal stable thin films.