Control of Nanophase Defects During Ceramic Melt Processing of Bi2Sr2CaCu2O8+x High Tc Superconductors

Published

February 19, 2017

Author(s)

T J. Haugan, Winnie Wong-Ng, Lawrence P. Cook, H J. Brown, L Swartzendruber

Abstract

To improve the critical current density of Bi₂Sr₂CaCu₂O_8+x high temperature superconductors (HTS) in high magnetic field applications (> 1 T from 20 K to 50 K), it is necessary to introduce a high density (approximately equal to} 5 per 100 nm in a linear direction) of nanosize (approximately equal to} 3-20 nm) defects directly into the superconductor. The addition of non-superconducting or flux pinning defects pins the magnetic field that enters the type II superconductor in interacting vortex structures (individual Φ _o = 2.07 x 10^-11 T cm²). Our approach to this problem is to introduce nanophase defects which have minimal chemical interaction with the superconductor phase. A complication of using this method, however, is that nanosize defects can quickly coarsen during the melt-growth methods typically used for processing HTS materials. Therefore a challenge is to add nanophase defects that do not coarsen or otherwise affect the processing of the superconductor. This paper shows initial results obtained with addition of 5 % to 25 % volume fraction defects (nanosize Al₂O₃, nanosize Au, submicrometer (Sr,Ca)¹⁴Cu₂₄O₄₁, and carbon nanotubes) to Bi₂Sr₂CaCu₂O_8+x thick films processed on Ag foils. Addition of nanosize defect particles in general improved flux-pinning properties from 20 K to 50 K, and greatly inhibited secondary Sr-Ca-Cu-O defect formations. Nanosize Al₂O₃ was observed to react with the Bi:Sr:Ca:Cu:O matrix after melting was initiated (> 870 C), to form solid-solution (Sr,Ca)₃Al₂O₆ phase with Sr:Ca ratio varying less than 10 % of the Sr:Ca ratio of the Bi:Sr:Ca:Cu:O precursor matrix. The (Sr,Ca)₃Al₂O₆ phase formed as submicrometer particles, however some coarsening to 1 mm to 5 mm size was noted for longer melt processing times (or higher temperatures). Addition of (Sr,Ca)¹⁴Cu₂₄O₄₁ phase defects did not significantly increase Jc, and particles were observed to coarsen quickly to 2 mu)m to 50 υm size. Addition of nanophase Au particles caused a significant problem for processing by completely suppressing 2212 c-axis oriented textured growth, however Au particles were not observed to coarsen. Addition of carbon nanotube defects produced submicrometer defects, however reduced c-axis oriented texture growth, altered phase assemblages, and reduced transport J_c(0T, 30K).

Citation

Electronic Publication

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Keywords

ceramic melt processing, nanophase defects, superconductors

Citation

Haugan, T. , Wong-Ng, W. , Cook, L. , Brown, H. and Swartzendruber, L. (2017), Control of Nanophase Defects During Ceramic Melt Processing of Bi2Sr2CaCu2O8+x High Tc Superconductors, Electronic Publication, [online], None (Accessed October 7, 2025)