Growth rate of YBCO-Ag superconducting single grains

J V J Congreve,A R Dennis,J H Durrell,D A Cardwell,Y H Shi

doi:10.1088/1757-899x/279/1/012027

J V J Congreve, A R Dennis + Show 3 more

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https://doi.org/10.1088/1757-899x/279/1/012027

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Abstract

The large scale use of (RE)Ba2Cu3O7 bulk superconductors, where RE=Y, Gd, Sm, is, in part, limited by the relatively poor mechanical properties of these inherently brittle ceramic materials. It is reported that alloying of (RE)Ba2Cu3O7 with silver enables a significant improvement in the mechanical strength of bulk, single grain samples without any detrimental effect on their superconducting properties. However, due to the complexity and number of inter-related variables involved in the top seeded melt growth (TSMG) process, the growth of large single grains is difficult and the addition of silver makes it even more difficult to achieve successful growth reliably. The key processing variables in the TSMG process include the times and temperatures of the stages within the heating profile, which can be derived from the growth rate during the growth process. To date, the growth rate of the YBa2Cu3O7-Ag system has not been reported in detail and it is this lacuna that we have sought to address. In this work we measure the growth rate of the YBCO-Ag system using a method based on continuous cooling and isothermal holding (CCIH). We have determined the growth rate by measuring the side length of the crystallised region for a number of samples for specified isothermal hold temperatures and periods. This has enabled the growth rate to be modelled and from this an optimized heating profile for the successful growth of YBCO-Ag single grains to be derived.

Highlights

Single grain (RE)Ba2Cu3O7 bulk high temperature superconductors (HTS), where require bulk (RE)=Y, Gd or Sm, have the ability to trap large magnetic fields, typically of more than an order of magnitude larger than those generated by conventional permanent magnets [1, 2]
Practical applications require bulk (RE)BCO to be fabricated in the form of large single grains, since the presence of high-angle grain boundaries in (RE)Ba2Cu3O7 superconductors prevent the flow of current
As the growth-front advances, too much silver is present to be pushed with the growth front and it is forced to move into the pores already present within the solidifying single grain structure

Summary

Introduction

Single grain (RE)Ba2Cu3O7 bulk high temperature superconductors (HTS), where RE=Y, Gd or Sm, have the ability to trap large magnetic fields, typically of more than an order of magnitude larger than those generated by conventional permanent magnets [1, 2]. This potentially enables a wide range of applications including Maglev trains, energy storage flywheels, rotating electrical machines and trapped flux devices [35]. A carefully considered heating profile is crucial to the successful growth of single grain bulk superconductors for the top seeded melt growth (TSMG) processing technique, in particular [18, 19]

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