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Title: Improvement in the growth and superconducting properties of bulk Sm-Ba-Cu-O superconductors fabricated in air
Author: Zhao, Wen
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2017
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Sm-Ba-Cu-O (SmBCO), which is a member of rare-earth barium cuprate [(RE)BCO] high-temperature superconductors, has significant potential for practical applications due to its higher critical transition temperature (Tc), higher critical current density (Jc), the so-called ‘peak effect’ characteristic at relatively high applied magnetic field and higher irreversibility field than that of the more established YBCO. The aim of this study is to investigate and overcome the obstacles in fabricating SmBCO bulk superconductors in air, to further improve their superconducting properties and, finally, to scale-up the fabrication of SmBCO single grains, therefore realising the engineering applications of this technologically important material. A modified seeding technique using an MgO-NdBCO generic seed accompanied by a buffer layer has been developed to process the SmBCO system to increase the success rate of growing single domain, bulk SmBCO superconductors in air via a top-seeded melt growth process using a conventional chamber furnace. Subsequently, the effects of doping in SmBCO bulk superconductors on the performance of SmBCO superconductors containing different dopants are discussed based on an analysis of their superconducting properties, including Tc and Jc, and on the microstructures of the samples. Furthermore, the scale-up of SmBCO bulk superconductors has been achieved by the addition of silver to the precursor powders and the introduction of a Y-123 layer beneath the SmBCO bulk pre-forms. Finally, trapped field measurements on successfully grown SmBCO bulk superconductors up to 41 mm in diameter have been performed and used to demonstrate significantly improved field trapping ability due to the optimization of the processing and composition of the SmBCO system. An Ag-SmBCO single grain of diameter 31 mm has achieved 1.033 T at 77 K, which is the highest value of trapped field reported worldwide for SmBCO samples of a similar size grown in air.
Supervisor: Cardwell, David Sponsor: China Scholarship Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
Keywords: High-temperature Superconductors ; SmBCO ; Superconducting properties