Dependence of critical current properties on the thickness of the superconducting layer inYBCO coated tapes

Abstract

The dependence of the superconducting layer thickness onthe critical current properties was investigated in the range of0.27–2.0 µm for YBCO coated tapes made by PLD processing on IBAD substrates.The critical current density at low fields in the direction of thec-axis was found to decrease with the increasing thicknessd inproportion to d−1/2 up to 1 µm. This seems to agree with the prediction of the two-dimensional collective pinning of randompoint pins. However, this dependence did not change over a wide temperature range of 5–60 Kand the critical thickness for the two-dimensional pinning was found to be much smaller than1 µm. This result suggests that the observed thickness dependence does not come from the pinningmechanism but simply from the change of the superconducting layer structure with increasingthickness. The effect of flux creep on the critical current properties at high temperatures isalso investigated, and the observed thickness dependences of irreversibility field andn-value are compared with the theoretical predictions of the flux creep-flow model.