Development of surface planarization process using MOD-Gd-Zr-O layer

Abstract

REBa₂Cu₃O _y (RE: rare-earth element, REBCO) coated conductors (CCs) have a high critical current density (J _c) under a magnetic field at the liquid nitrogen temperature and a potential performance for high-magnetic field applications. In order to prepare a biaxially highly oriented REBCO, a highly-textured buffer layer is required. The ion-beam assisted deposition (IBAD) technique is one of the promising techniques for preparation of the highly-textured layer even on the non-textured metallic substrate such as Hastelloy™. However, excellent surface smoothness and uniformity are indispensable to the non-textured metallic substrate using the IBAD technique. Therefore, an inexpensive surface planarization process has been required for fabrication of REBCO CCs with low-cost. In this study, we have investigated the surface planarization using the metal-organic deposition (MOD) method for the IBAD-MgO texturing. The Gd-Zr-O (GZO) planarization layer was prepared by MOD method on roughly-polished Hastelloy™ C-276 substrate. The surface roughness values (R _a) of MOD-GZO planarization layer became smaller than that of the Hastelloy™ C-276 with increase in coating times. Minimum R _a of the MOD-GZO planarization layer achieved less than 2 nm, which is smooth enough for obtaining the highly-textured IBAD-MgO film. The in-plane grain alignment of CeO₂ film deposited on sputter-LaMnO₃ / IBAD-MgO / MOD-GZO / Hastelloy™ C-276 substrate by the pulsed laser deposition was 4°, and high J _c value of 2.5 MA/cm² (1.8 μm-t) was obtained for MOD-YBCO film fabricated on it. The CCs using MODGZO planarization layer provided the delamination strength over 70 MPa, which was compatible with conventional structure of CCs.