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 text ured substrates. Critical current transport measurements in zero field show ed j(c) values up to 0.7 MA/cm(2). FWHM of x-ray phi -scans of the buffer l ayer and the YBCO were about 9 degrees and 11 degrees, respectively. The ox ide buffer was a bilayer, composed of CeO2, Y2O3 or YSZ in various combinat ions and thicknesses. Since the Ni-diffusion barrier efficiency strongly de pends on the buffer morphology detailed SEM and FIB (focussed ion beam) stu dies of the different buffer systems were carried out. They revealed a colu mnar but dense growth characteristic in the buffer bilayers but also defici encies at the substrate surface. These observations indicate that a smooth substrate surface without significant impurities is essential for YBCO coat ed conductors.