Atom-replaced pins in a Y-based superconductor—single-crystalline perovskite structure including both PrBa₂Cu₃O_7−xand YBa₂Cu₃O_7−y

Abstract

Metal organic deposition using trifluoroacetates (TFA-MOD) provides many uniform superconductors on long metal tapes. The large numbers of long wires have been applied for power grids or superconducting fault current limiters. The related applications worked for a long time without fatal trouble. The quasi-liquid produced during the firing process assisted the perfectly uniform structure in TFA-MOD. On the other hand, when it was desired to introduce artificial pinning centers, the quasi-liquid also enlarged the diameter of the artificial pinning centers to several tens of nanometers. In other words, due to the nature of TFA-MOD, there is very little chance of using TFA-MOD to prepare several nm-sized artificial pinning centers. By proposing atom-replaced pins (ARPs), we aim to overcome the impasse. ARPs are realized by replacing yttrium (Y) with praseodymium (Pr) whose valence number changes from 3+to approximately 4+. Analytical results suggested that Pr makes pinning centers on a PrBa 2 Cu 3 O 7−x (PrBCO) unit cell, and the weak-linked superconductivity derived from PrBCO extends to the adjacent unit cells in the a/b-plane. J c decrease by Pr is five times as large as the volume fraction of Pr in the Y-site of the perovskite structure. On the other hand, T c does not show large degradation in YBCO including 10% PrBCO. These results suggest that PrBCO unit cells are fully dispersed in YBa 2 Cu 3 O 7−y matrix. With regard to J c in the magnetic field, (Y 0.98 , Pr 0.02 )BCO has been slightly improved compared with pure YBCO only in the region of high temperature and low magnetic field of less than 1 T.

Chemical Solution Deposition of YBCO Films with Gd Excess

“…Actually, the present XPS and TEM investigations suggested that also in our samples, Y substitution by Gd occurred despite the unfavorable conditions for GdBCO nucleation (pO 2 too high and thermal treatment ramp rates too slow for GdBCO film [8,9]). The findings of our work were in agreement with previous results obtained by Hayashi et al on (Y,Pr)BCO films [48]. The authors of that work assumed that both YBCO and PrBCO formed, although PrBCO nucleation requires a pO 2 at least 1000 times lower than that necessary for YBCO formation.…”