WBP 2-3 Flux pinning properties of hafnium doped Gd 123 films fabricated by fluorine-free MOD method with multistage heat treatment *

Metal Organic Deposition using Trifluoroacetates deposition (TFA-MOD) is a low-cost nonvacuum approach that offers high reproducibility, making it one of the best candidates for preparing uniform long tape of rare-earth barium copper oxide (REBCO). Although many groups have improved critical current density (Jc) for REBCO superconductors in a magnetic field by introducing artificial pinning centers (APCs) such as BaMO3 fabricated by Pulsed Laser Deposition or Metal Organic Chemical Vapor Deposition, these films have less uniformity and degraded critical temperature (Tc) values. Furthermore, it is difficult to introduce APCs by TFAMOD. We therefore attempted to establish a new perovskite structure in which nonsuperconducting PrBCO co-exists with superconducting REBCO. Here, PrBCO serves as an atom replaced pin (ARP). We prepared a purified coating solution and obtained REBCO superconductor dispersed with PrBCO. TEM observation of the film in which the YBCO matrix was substituted with 10 mol% PrBCO revealed a completely uniform structure as shown in Fig. (a). XRD results for the film showed a single REBCO(00n) phase. The above two results suggest that ultimately dispersed PrBCO unit cells co-exist with YBCO unit cells. Figure (b) shows the relationship between substituted Pr concentration at Y sites and Tc. At concentrations of up to 8 mol% Pr, Tc values were kept around 90.7 K. ARPs appeared not to degrade the Tc value because they do not withdraw oxygen from neighboring YBCO unit cells as reported for BaMO3 pins. To improve Jc-B properties, dispersed PrBCO needs to be accumulated at one site. We added 2 mol% Pr, 2 mol% Sm (as large unit cells) and 4 mol% Tm (as small unit cells) to YBCO and were able to improve JcB properties as shown Fig. (c).