Transport critical current density of melt-processed (QMG) YBa2Cu3Ox bulk superconductors

Abstract Transport critical currents of melt-processed (QMG) YBa 2 Cu 3 O x bulk superconductors were measured by a d.c. four probe method. The QMC bulk specimens have high J c characteristics of ≈ 1 × 10 4 A cm −2 at 5 T for the magnetic field parallel to a–b plane. The angular dependence of J c upon the direction of applied magnetic field showed some characteristic features which could not be described by simple flux pinning. This indicates that anisotropic pinning is relatively strong. The pinning caused by the layered structure, twin boundaries and oxygen deficiency, as well as pinning by the Y 2 BaCuO 5 phase, play important roles in determining the J c of the QMG YBa 2 Cu 3 O x bulk superconductors.