Relationship between film thickness and the critical current of YBa2Cu3O7-δ-coated conductors

During the development of YBa2Cu3O7-delta (YBCO) coatings on flexible metal tapes, it has become evident that the achievable critical current (I-c) reaches a maximum value of about 200 A per cm of conductor width at a coating thickness of 1-2 mu m. Additional YBCO beyond this thickness can actually reduce I-c. To investigate, critical current density (J(c)) has been measured for samples with YBCO ranging from 0.39 to 6.3 mu m in thickness. Several films were thinned by ion milling and remeasured with two significant results: almost no supercurrent is carried at thickness levels above 2 mu m; and for films thicker than 3 mu m, J(c) is drastically reduced near the substrate as well. (C) 1999 American Institute of Physics. [S0003-6951(99)04249-7].