Development of Long YBCO-coated Conductors Using IBAD-PLD Method
—Long Fabrication of Self-epitaxial PLD-CeO₂ Cap Layers on IBAD Tape—

Abstract

We found that a PLD-CeO₂ cap layer on an IBAD-Gd₂Zr₂O₇ (GZO) tape can make a high grain alignment without ion-beam assistance such as the IBAD process. We call this phenomenon “self-epitaxy in a PLD-CeO₂ cap layer”. At present, we are developing long tapes by the Reel-to-Reel process for the self-epitaxial PLD-CeO₂ cap layer on an IBAD-GZO tape. A 108 m-long tape with a PLD-CeO₂ cap layer was obtained. The delta phi values of the buffer layer were improved to 4.3-4.8 degrees of PLD-CeO₂ from 13.3-14.0 degrees of IBAD-GZO. Although the fabrication rate of the PLD-CeO₂ cap layer was as fast as 5-6 m/h, that of the IBAD-GZO was 1 m/h. Then, we tried to improve the overall fabrication rate of the total buffer layers using a thin IBAD layer and the self-epitaxial PLD-CeO₂ cap layer. A PLD-CeO₂ cap layer was deposited at a tape transfer speed of 2.5 m/h on a 55 m-long IBAD-GZO tape with the delta phi values of 23.1-24.0 degrees fabricated at 2 m/h, which was two times faster than the conventional IBAD process. As a result, the delta phi values of the PLD-CeO₂ cap layer were in the range of 8.6-10.4 degrees. The fabrication rate throughout all of the processes for buffer layers was achieved to be 2 m/h. It was found that PLD-CeO₂ was effective for enhancing both the fabrication rate and grain alignment.