Critical transport current density in sintered oxide superconductors with high critical temperature

Percolative critical transport current density in sintered Y–Ba–Cu–O superconductors is estimated by taking into account the effect of anisotropies in the upper critical field and the pinning structure. This value is much smaller than the estimate for the optimized situation, where misorientation between the magnetic field and anisotropic pinning structures does not occurs. As the volume fraction of the superconducting region becomes small, the critical transport current density decreases drastically due to a decrease in the percolation probability of the current. To improve the transport property, it is necessary to align the orientation of grains or to introduce isotropic pinning centers, in addition to increasing the superconducting volume fraction.