Electromagnetic Properties of $(\hbox{Gd}, \hbox{Y}) \hbox{Ba}_{2}\hbox{Cu}_{3}\hbox{O}_{\rm x}$ Superconducting Tapes With High Levels of Zr Addition

The dependence of the critical current density (J_c) on the orientation of applied magnetic fields was studied in Zr-doped ( Gd, Y)Ba₂Cu₃Ox tapes fabricated by metal organic chemical vapor deposition. The in-field performance of J_c of (Gd, Y)Ba₂Cu₃Ox tapes with Zr-doping levels of 7.5-30 at.% was investigated up to 5 T over a temperature range of 40-77 K. The highest critical currents (I_c) at H ||c and the highest values of minimum I_c in angular dependence measurements were achieved in the tapes with 20% Zr doping over a broad range of temperature and magnetic field conditions measured. The electromagnetic properties have been related to the changes in BaZrO₃ content and microstructure.

I. Introduction

As the most representative material of high temperature superconductors (HTS), REBCO thin film tapes are promising for high magnetic-field applications because of their high critical current and high irreversible field. Many techniques have been used to fabricate REBCO thin film tapes, such as metal organic chemical vapor deposition (MOCVD) [1], [2], pulsed laser deposition (PLD) [3], [4] and metal organic deposition [5]. The depression in critical current of REBCO in an applied magnetic field is however a major challenge in applying REBCO thin film in high magnetic-field applications. Nanoscale defects such as (BZO) have been employed as pinning centers to improve critical current density in magnetic fields by better flux pinning [6]–[8]. Driscoll et al. [6] introduced BZO pinning defects in YBCO films grown by PLD in which BZO nano-particles are incorporated in the films from the source target of a ceramic BZO/YBCO mixture. Selvamanickam and Chen et al. [9] reported the enhancement of flux pinning in Zr-doped GdYBCO tapes made by MOCVD. At 77 K 1 T, the magnetic field performance of GdYBCO with Zr-doping levels from 0 at.% to 15 % at.% made by MOCVD has been systematically studied, and the highest critical currents were achieved at 7.5 % Zr doping at 77 K, 1 T applied perpendicular to the film surface [9]. Recently, our group demonstrated that at temperatures of 40 K and below however, higher levels of Zr addition results in superior flux pinning [10], [11]. GdYBCO tapes with 15% Zr addition were found to perform significantly superior to those with 7.5% Zr addition over a temperature range of 1–9 T at 20 to 40 K [10]. We had also investigated the structural changes in GdYBCO films with Zr addition levels from 0 to 30 at.% in an effort to determine the reduction in critical current at 77 K and zero magnetic fields with increasing Zr addition [11]. Using a modified MOCVD process, the critical current degradation with increasing Zr content was substantially reduced with essentially no drop in up to 15% Zr addition [11]. In this work, the influence of Zr doping levels from 7.5 to 30 at. % on the electromagnetic properties of films made by the improved MOCVD process were investigated at low temperatures and high magnetic fields over a wide angular range of field orientations. Fig. 1.

Zero-field critical current at 77 K of Zr-doped GdYBCO tapes with Zr doping levels of 7.5 30 at.%.

Fig. 2.

Angular dependence of critical current of GdYBCO tapes with 7.5–30 at. % Zr doping at (a) 77 K 1 T, (b) 77 K 3 T, (c) 65 K 1 T, (d) 65 K 3 T, (e) 50 K 3 T, (f) 50 K 5 T, (g) 40 K 3 T, and (h) 40 K 5 T.