Investigation of buffer layers for YBCO coated conductors

Biaxially aligned, heteroepitaxial oxide buffer layers and superconducting YBa2Cu3O7-x (YBCO) thin films were deposited with PLD on Ni-based cube textured substrates. Critical current transport measurements in zero field showed j(c) values up to 0.7 MA/cm(2). FWHM of x-ray phi -scans of the buffer layer and the YBCO were about 9 degrees and 11 degrees, respectively. The oxide buffer was a bilayer, composed of CeO2, Y2O3 or YSZ in various combinations and thicknesses. Since the Ni-diffusion barrier efficiency strongly depends on the buffer morphology detailed SEM and FIB (focussed ion beam) studies of the different buffer systems were carried out. They revealed a columnar but dense growth characteristic in the buffer bilayers but also deficiencies at the substrate surface. These observations indicate that a smooth substrate surface without significant impurities is essential for YBCO coated conductors.