Correlation between cation disorder and flux pinning in the y Ba2 Cu3 O7 coated conductor

A correlation has been observed between the through-thickness cation disorder level in Y Ba2 Cu3 O7 (YBCO) coated conductor films and the commonly observed falloff in layer-by-layer through-thickness critical current density (Jc) of YBCO films produced by pulsed laser deposition (PLD) on single crystal substrates. The amount of cation disorder with respect to the aggregate, c -axis-textured YBCO content was measured by Raman spectroscopy methods combined with step milling of 1.5-1.7 μm thick YBCO films. For PLD YBCO films on single crystal strontium titanate, the Raman results indicate a sharp drop off in cation disorder from the substrate surface outward toward the top of the YBCO film. This drop off appears to level out in the 0.4-0.6 μm range, after which the cation disorder level remains relatively constant. This trend appears to be very much like the one reported by others for the through-thickness Jc dependence of PLD YBCO on single crystal specimens. Conversely, metal-organic-deposition-produced YBCO films on rolling assisted biaxially textured substrates do not exhibit a strong through-thickness Jc dependence or a measurable change in the relative amount of cation disorder, again through thickness. The results of this study suggest that cation disorder in the YBCO lattice leads to increased flux pinning strength and that the cation disorder domains most probably occur on a size scale in the range from one to perhaps a few YBCO unit cell dimensions.