Melt-processed light rare earth element - Ba - Cu - O

Abstract

Unlike Y123 which forms only a stoichiometric compound, the light rare earth elements (LREs: La, Nd, Sm, Eu, Gd) form a solid solution LRE 1+x Ba 2−x Cu 3 O y . The presence of such solid solution caused a depression in the superconducting transition temperatures (T c ), particularly for La123, Nd123 and Sm123 when they are melt processed in air. Recently, we have found that the T c of these LRE123 superconductors can greatly be enhanced when they are melt processed in a reduced oxygen atmosphere. Furthermore, J c values of these superconductors were larger than that of a good quality Y123 superconductor in high magnetic fields at 77 K. In this article, on the basis of our study over the last several years, the melt processes for LRE-Ba-Cu-O are described, the microstructural and superconducting properties of the superconductors are reviewed and the flux pinning mechanism is also discussed.

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.…”

Nanocomposite RE-Ba-Cu-O Bulk Superconductors

“…As a result, the growth rate of (LRE) 1+x Ba 2-x Cu 3 O 7-y is relatively fast compared to that of Y-123. Here it is worth mentioning that (LRE) 1+x Ba 2-x Cu 3 O 7-y inherently possesses a solid solution between LRE and Ba sites and a large x leads to a reduction of the T c and/or even non transition to the superconductivity [5]. In order to suppress x values, oxygen controlled melt growth, OCMG, in which a whole growth process is conducted in a reduced oxygen partial pressure, has been proposed [6].…”

Solid-liquid phase equilibria on the GdBa2Cu3O7-δstability phase diagram in low oxygen pressures (1 - 100 mTorr)

“…GdBCO has been known to exhibit higher J c in magnetic fields in comparison with YBCO [1], and thus regarded as a strong alternative to YBCO for coated conductors (CCs). In such a reason, high-performance GdBCO CCs have been fabricated by PLD (pulsed laser deposition) [2,3] and RCE-DR (reactive co-evaporation by deposition and reaction) [4,5] processes.…”