THICKNESS DEPENDENCE QF CRITICAL CURRENT DENSITY IN IBAD/PLD YBCO COATED CONDUCTOR

摘要

The dependence of the critical current properties on superconducting layer thickness was investigated in the range of 0.5 to 1.5 mu m for YBCO coated tapes made by the PLD processing on IBAD substrates.The critical current density at low fields in the direction of the c-axis was found to decrease with the increasing thickness d in proportion to dr~(-1/2).This seems to agree with the prediction of the two-dimensional collective pinning of random point pins.However,this dependence did not change over a wide temperature range of 5 to 77 K and the critical thickness for the two-dimensional pinning was found to be much smaller than 0.5 mu m.This result suggests that the observed thickness dependence does not come from the pinning mechanism but simply from the change in the superconducting layer structure with increasing thickness.The effect of flux creep on the critical current properties at high temperatures is also investigated,and the observed thickness dependences of irreversibility field and n-value are compared with the theoretical predictions of the flux creep-flow model.It is clarified that the effect of the transverse flux bundle size on the pinning potential should also be considered for a detailed analysis of the thickness dependence of the irreversibility field.