Investigation on Preparation and Properties of Sm-Ba-Cu-O Bulk Superconductor

　　Investigation on Preparation and Properties of Sm-Ba-Cu-O Bulk Superconductor
　　REBa2Cu3O7-δ(RE123)bulk superconductors have significant potential in engineering applications,such as maglev,magnetic bearings,permanent magnets, fly wheel energy storage systems and superconducting motors,since they have high critical temperature(Tc),high critical current density(Jc)and strong trapped magnetic fields.As the anisotropy of the crystal structure of Y-system high-temperature superconductor,to make the current density reach the level of utility,the first point is to grow preference-oriented crystal.Single domain superconducting bulk can be produced by top seeded melting texture growth method(TSMTG).The bulk materials grow along with the seed crystal orientation and form the c-axis oriented single domain bulks.The Tc of Y123 was arrived at 90 K which provided a wider foreground for the utility of high temperature superconductors.The Sm 123,obtained by substituting Y by the rare earth Sm in Y123,is potentially attractive,because the Sm123 have not only neodymium magnets a higher Tc than Y123 but also a higher critical current density(Jc)in high magnetic fields.In this thesis,we prepared Sm-Ba-Cu-O superconducting bulk by the isothermal growth progress based on TSMTG,and researched bulks superconducting properties and organization structure.In chapter one,we introduce the potential applications of the bulk superconductors and summarize the preparing methods for the bulk superconductors.We made the research objects and contents for the thesis.In chapter two,the precursor powders were prepared by quick decomposed gel method.The powder purity,size and carbon content were the three very important parameters for the preparation of the Sm123 powders.
　　The experiment results show that the optimal sintering temperature is about 850℃and dwelling for 10 hours.The particle size of Sm211 phase effect on the quality of Sm-Ba-Cu-O superconductors,so a proper sintering temperature and ball milling process have to be carried out.The optimal temperature is about 950℃to obtain fine and purity Sm211 phase.In chapter three,we obtained the Sm-Ba-Cu-O domain bulk superconductors by the isothermal growth progress.For the study of parameters of Sm-Ba-Cu-O bulk,we found that the exhausting air time,the melting temperature,the melting time,the temperature of begin to grow,the growing time,the annealing temperature and time in flowing pure oxygen are very important to the preparation for the single domain Sm-Ba-Cu-O superconducting bulks.For the Sm-Ba-Cu-O bulks,the pre-sintering temperature must be heated to 950℃and held for 40 hours to improve the density and intensity.TheΦ18mm bulk sample melt at 1065℃for 1 http://www.chinamagnets.biz hour not only could produce enough liquid but also could obtain better morphology for the bulk.The isothermal growth technology enables the bulk to have a great growth rate.We found that the proper growth temperature of Sm-Ba-Cu-O single domain bulk was between 1045℃and 1048℃.in order to get good superconducting properties,the melted bulk samples must be annealing in flowing pure oxygen.The best treatment forΦ15mm bulk sample is to anneal at 320℃for 100 hours.In chapter four,Sm-Ba-Cu-O bulks were prepared by isothermal growth progress,which have good macroscopic single domain morphology and microscopic organization structure and have high superconducting properties.In chapter five,Sm-Ba-Cu-O single domain bulks with different Sm amont were prepared and the characterized magnetization,XRD,and SEM analyses.It is found that the using of nanopowder precursors avoids the formation of large Sm211 particles,thus decreases the size of pinning centers.However,a relatively small amount of Sm211 shows a drastic suppression on superconductivity of Sm-Ba-Cu-O melt-textured-bulks due to the enhanced partial replacement of Ba with Sm in SmBa2Cu3O7,which degrades the superconducting properties of Sm-Ba-Cu-O single domain bulks.