High critical currents in heavily doped (Gd,Y)Ba₂Cu₃O_x superconductor tapes

REBa₂Cu₃O_x ((REBCO), RE = rare earth) superconductor tapes with moderate levels of dopants have been optimized for high critical current density in low magnetic fields at 77 K, but they do not exhibit exemplary performance in conditions of interest for practical applications, i.e., temperatures less than 50 K and fields of 2–30 T. Heavy doping of REBCO tapes has been avoided by researchers thus far due to deterioration in properties. Here, we report achievement of critical current densities (J_c) above 20 MA/cm² at 30 K, 3 T in heavily doped (25 mol. % Zr-added) (Gd,Y)Ba₂Cu₃O_x superconductor tapes, which is more than three times higher than the J_c typically obtained in moderately doped tapes. Pinning force levels above 1000 GN/m³ have also been attained at 20 K. A composition map of lift factor in J_c (ratio of J_c at 30 K, 3 T to the J_c at 77 K, 0 T) has been developed which reveals the optimum film composition to obtain lift factors above six, which is thrice the typical value. A highly c-axis aligned BaZrO₃ (BZO) nanocolumn defect density of nearly 7 × 10¹¹cm⁻² as well as 2–3 nm sized particles rich in Cu and Zr have been found in the high J_c films