Microstructure Analysis of High-Quality Buffer Layers on Textured NiW Tapes for YBCO Coated Conductors

Epitaxial CeO₂ seed layer and multiple CeO₂/YSZ/CeO₂ buffer layers were in-situ deposited in a reel to reel pulsed laser deposition chamber on rolling assisted biaxially textured NiW tapes. Epitaxial relationship and surface morphology of each layer were systematically studied by x-ray diffraction (XRD), high resolution scanning electron microscope (SEM) and atomic force microscope (AFM). The in-plane texture of CeO₂ cap layer is 6-7 degrees, which was comparable to NiW substrate. During deposition parameter optimization, it was observed that the orientations of YBCO layers were related with individual NiW grains. Although c-axis orientation was the dominant orientation of YBCO films under optimum deposition conditions, a small amount of a-axis orientation was observed in YBCO films. These sun-micro scale a-axis orientated YBCO grains were not uniformly distributed in YBCO films, but only located inside a small percentage of NiW grains. SEM observation showed that grain size of buffer layers was sensitive to deposition parameters. The influence of buffer layer grain size and surface roughness on the epitaxial quality of YBCO layers was investigated.