Transport critical currents of melt-processed (QMG) YBa2Cu3Ox bulk superconductors were measured by a d.c. four probe method. The QMC bulk specimens have high Jc characteristics of ≈ 1 × 104 A cm-2 at 5 T for the magnetic field parallel to a-b plane. The angular dependence of Jc 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 Y2BaCuO5 phase, play important roles in determining the Jc of the QMG YBa2Cu3Ox bulk superconductors.
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