Transport critical currents and flux pinning in melt-grown YBa 2Cu 3O 7−δ

Abstract

The critical current and flux pinning properties of melt grown YBa 2Cu 3O 7−δ bulk material were investigated by transport measurements and V-I characteristics. A J c of 16 000 A cm −2 in zero field and 3000 A cm −2 in 1 T at 77 K was obtained using a criterion of 3.3 μV cm −1. No features of granularity could be detected as J c showed no hysteresis with increasing or decreasing field. By considering a distribution of activation energy U 0 together with the correlation volume of flux bundles V c and the pinning range r p, the measured V-I characteristics in the flux creep regime were found to be consistent with that of thermally activated flux flow (TAFF). The temperature and field dependence of the derived V c r p points to a collective pinning mechanism by point defects. The depinning current J c, one to tow orders of magnitude higher than the transport J c, was also obtained by using the U 0 and V c r p deduced from the V-I characteristics.