Progress in melt-processed (Nd Sm Gd)Ba₂Cu₃O_ysuperconductors

Abstract

This comprehensive survey deals with the melt-growth process and characterization of the novel class of ternary materials, (Nd,Sm,Gd)Ba 2 Cu 3 O y 'NSG-123'. Microstructure observations by optical microscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM) revealed the presence of sub-micron secondary phase (RE 2 BaCuO 5 , 211) particles uniformly dispersed in the 123 matrix that enhance flux pinning at low fields and improve the performance of this material. The energy-resolved TEM-EDX analysis clarified that small particles consist mainly of Gd 2 BaCuO 5 'Gd-211', irrespective of the initially added secondary phase (Gd-211 or NSG-211). Dark-field TEM observations showed that the NSG-123 matrix had a high density of RE-rich RE 1+x Ba 2−x Cu 3 O y (RE-123ss) clusters 3-10 nm in size. These small clusters enhance pinning at intermediate fields. The scaling analyses of the volume pinning force density at 77 K made on NSG-123 samples with varying 211 contents of various secondary phases showed the secondary peak at normalized fields as high as 0.45, which might indicate the activation of T c pinning mechanism. Trapped field measurements proved that silver was the key element to improve the mechanical strength of NSG-123 materials. Record trapped-field values at high magnetic fields can be obtained at 77 K with appropriately large sized NSG-123 samples.

Progress in Nanoengineered Microstructures for Tunable High‐Current, High‐Temperature Superconducting Wires

“…It is the short coherence length (≈ 1.5 nm) of YBCO that necessitates nanoscale pinning centers. [34,35] Therefore, a high density of nano-scale defects is needed to provide the flux pinning centers to support the highest possible levels of J c . Recent successes on the introduction of inclusions during pulsed laser deposition (PLD) of YBCO films for enhanced pinning in applied fields by Driscoll et al, and Haugan et al, pointed to a deposition-controlled methodology for addressing this problem.…”

Effect of doping on flux pinning of GdBa2Cu3O7−y

“…This higher J c of S2 at low temperatures and fields maybe related to the fact that S2 has fine Gd-211 particles in its starting powder, which were the effective pinning centers. 10,11 Whereas in S1 less Gd-211 might be on the precipice. Less Gd-211 phase means saving some Gd ions in S1.…”

“…To avoid excessive LRE-Ba substitution, variations of the MTG processes, such as postannealing in Ar atmosphere, using of Barich precursors, and employing large crystallization rate, have been developed. 10,11 In addition, some amount of the LRE 2 BaCuO 5 ͑LRE-211͒ phase are added into the LRE-123 systems to improve the flux pinning. Because GdBa 2 Cu 3 O 7−y ͑Gd-123͒ in the LRE-123 systems shows the slightest Gd-Ba substitution even when fabricated in air, and the "in air" processing will lower fabricating cost, the process of fabricating Gd-123 in air has received much more interests.…”

Effect of Zr addition on critical current density of (Y,Gd)Ba2 Cu3 O y and (Y,Eu,Gd)Ba2 Cu3 O y thin films deposited by TFA-MOD process

“…Recently, the issue of improving J c has been successfully addressed through various methods. In particular, substitution of rareearth elements and addition of a second phase (nonsuperconducting) are very successful and easy methods to improve flux pinning [3][4][5]. Our previous studies have shown that proper quantities of Gd and/or Eu substitution in Y site significantly increased J c .…”

“…Studies on the effect of Zr addition on J c of (Y, RE)Ba 2 Cu 3 O y thin films showed that the Zr addition can markedly enhance the infield J c values of (Y, Gd)Ba 2 Cu 3 O y films, whereas it reduces that of (Y, Eu, Gd)Ba 2 Cu 3 O y films. 3 (001) single-crystal substrates using trifluoroacetic acid metal organic deposition (TFA-MOD) process. Stoichiometric Y(Eu, Gd), Ba, Cu acetates were dissolved into the mixed solution of deionized water and access trifluoroacetic acid.…”