Temperature dependence of transport critical current density for REBCO superconducting tapes deposited by MOCVD

The temperature-dependent transport critical current density ( Jc ) behavior of REBa2Cu3O7-delta (REBCO) superconducting tapes with various RE substitutions and combinations has been systematically studied in the temperature range of 4 K-77 K. The measured Jc values were found to be highly in accordance with JcT,B=Jc(0K,B)(1-T/Tc)s with the values of the exponent coefficients s ranging from 1.9 to 2.6 in the magnetic-field range of 1-5 T depending on RE ion(s), revealing the dominative pinning mechanism of flux core pinning. The RE-ionic-radius (r) dependences of JcT,B showed reversed trends for temperatures below and above 50 K, with Jc increasing with r at higher temperatures while it decreased with r at lower temperatures, which was consistent with previously reported results. In particular, the in-field Jc of REBCO tapes at 4 K as a function of r was consistent with the Jc -r trend for low temperatures. We propose to attribute the Jc -r trends to the higher charge carrier density and the lower critical transition temperature ( Tc ) in REBCO films with smaller r. The Gd0.5Yb0.5BCO tape with superior Jc at low temperatures exhibited the furthest diversion from the Jc -r trendlines due to enhanced correlated pinning by the high-density of vertically aligned second-phase nanocolumns in the film. The temperature dependence of Jc for REBCO tapes with a larger r was found to be more susceptible to the magnetic field. Meanwhile, the exponent coefficients s showed a more precipitous increase with the increasing magnetic field, partially due to the lack of effective pinning defects, which was also confirmed by the two-dimensional x-ray diffraction patterns and the higher alpha values. This work contributes to the study of the Jc of REBCO superconducting tapes below 20 K and leads to a deeper understanding of the temperature-dependent Jc behavior of REBCO films with various RE substitutions and combinations. This provides more comprehensive guidelines for the optimization of RE ions in REBCO for applications at specific temperatures and magnetic fields.