Progress in the continuous deposition of YBCO coated conductors by thermal co-evaporation

We report on recent progress towards the continuous deposition of YBCO Coated Conductors (CC) prepared by thermal coevaporation. This is an attractive vacuum technique thanks to the simplicity, low cost and intrinsic uniformity over large areas > 20 x 20 cm2. Here we describe the in situ preparation route of 1 um thick superconducting YBCO films deposited onto 100 nm thick CeO2 buffered Ni biaxially textured tapes using a simple-pass reel-to-reel system. In spite of the simple buffer layer architecture, we demonstrate the growth of dense and crack-free buffer layers with good biaxial texture and FWHM's values in the 5-7° range for both in- and out-of-plane orientations. This enables the subsequent growth of the YBCO layer with similar structural properties, zero-resistance Tc=86-87 K and transition widths DeltaTc<3 K. End-to-end critical current densities Jc's at 77 K and self-field measured by transport measurements are in the 1.5-2.5 MA/cm2 range for 1 m long samples. It is found that tape motion does not significantly affect the above properties. We specifically address the following critical points regarding: 1) the deposition by thermal or e-beam evaporation of crack-free CeO2 buffer layers; 2) the in situ oxidation of the YBCO layer using a novel supersonic nozzle: 3) the scaling-up of the deposition process using a new multi-chamber system. Thanks to the simple buffer layer architecture, we show that the present route is promising for the industrial production of CC with a competitive cost < 20 Euro/kA m.