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FABRICATION OF BULK (RE)BCO SUPERCONDUCTORS BY THE INFILTRATION AND GROWTH PROCESS: PAST, PRESENT AND FUTURE

Namburi, DK and Shi, Y-H and Cardwell, (2015) FABRICATION OF BULK (RE)BCO SUPERCONDUCTORS BY THE INFILTRATION AND GROWTH PROCESS: PAST, PRESENT AND FUTURE. In: Superconductivity Applications Today and Tomorrow. Nova Science Publishers Inc., New York.

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Abstract

Large, single grain bulk (RE)BCO high temperature superconductors have been the source of great excitement since their discovery in the late 1980’s. This chapter presents a brief review of the ‘Infiltration and Growth process’, which is one of the most promising fabrication techniques developed relatively recently, that enables the microstructure of these technologically important materials to be engineered effectively. The technical need for single grain (RE)BCO bulk superconductors is outlined in the preliminary section of the chapter, including their potential for a variety of high field engineering applications. Details of the Melt Growth (MG) and Infiltration Growth (IG) processing techniques for fabricating bulk (RE)BCO single grain superconducting materials are then presented, including details of the various critical parameters associated with the single grain growth process, such as the importance of seeding, the choice of seed crystal, heterogeneous nucleation and growth, the formation of non-superconducting inclusions and their role in flux pinning. The advantages and disadvantages of the MG and IG processing techniques are also described. The main focus of the chapter is to review the Infiltration and Growth process in the context of fabricating bulk (RE)BCO superconductors with special emphasis on YBCO and YBCO-Ag materials. This concentrates on the steps that enable successful fabrication of bulk (RE)BCO with improved microstructures, which, in turn, have the potential to achieve large critical current densities (Jc) and therefore to generate significant trapped fields. Various improvements made to the Infiltration and Growth process and their influence on the single-grain growth microstructure and superconducting properties are discussed. RE-based high temperature oxide superconductors, which are ceramic and granular in nature, are type II superconducting materials, in which Jc is governed largely by the sample microstructure. In particular, the presence of non-superconducting inclusions, defects such as twins and twin boundaries, which potentially resist the motion of flux against electromagnetic forces, is fundamental to achieving good superconducting properties. The need to optimise the size and distribution of non-superconducting phases in the superconducting matrix for optimum flux pinning is explained and the present state of the art outlined. The role of liquid phase in the IG process is critical to achieve appropriate and continuous infiltration during grain growth. In addition, this step in the process largely influences the nature of the single grain growth. The review also discusses the optimum liquid phase to achieve controlled, single grain growth. Results obtained for isothermal growth studies, and hence the choice of heat treatment, are presented and discussed. Various superconducting properties such as levitation force, the field dependence of Jc, trapped field and ac susceptibility measured for IG processed samples is also reviewed. Finally, the optimum configuration for the processing of bulk (RE)BCO samples by the IG process is described and the scope for further improving the process presented.

Item Type: Book Section
Uncontrolled Keywords: Infiltration Growth process superconductor, bulk trapped field superconducting properties microstructure mechanical property ceramics single grain YBCO preform optimisation oxygenation
Subjects: UNSPECIFIED
Divisions: Div C > Materials Engineering
Depositing User: Cron Job
Date Deposited: 17 Jul 2017 20:09
Last Modified: 03 Aug 2017 03:03
DOI: