Textured YBCO films grown on wires: Application to superconducting cables

摘要

Efforts to fabricate superconducting wires made of YBa _2Cu _3O _7 (YBCO) on La _2Zr _2O _7 (LZO) buffered and biaxially textured Ni-5at.%W (NiW) are described. Wires were manually shaped from LZO buffered NiW tapes. Different diameters were produced: 1.5, 2 and 3mm. The wires were further covered with YBCO grown by metal organic chemical vapor deposition (MOCVD). We developed an original device in which the round substrate undergoes an alternated rotation of 180°around its axis in addition to a reel-to-reel translation. This new approach allows covering the whole circumference of the wire with a YBCO layer. This was confirmed by energy dispersive x-ray spectroscopy (EDX) analysis coupled to a scanning electron microscope (SEM). For all wire diameters, the YBCO layer thickness varied from 300 to 450nm, and the cationic composition was respected. Electron backscattering diffraction (EBSD) measurements were performed directly on an as-deposited wire without surface preparation allowing the investigation of the crystalline quality of the film surface. Combining EBSD with XRD results we show that YBCO grows epitaxially on the LZO buffered NiW wires. For the first time, superconductive behaviors have been detected on round substrates in both the rolling and circular direction. J _c reached 0.3MAcm ~2 as measured at 77K by transport and third-harmonic detection. Those preliminary results confirm the effectiveness of the MOCVD for complex geometries, especially for YBCO deposition on small diameter wires. This approach opens huge perspectives for the elaboration of a new generation of YBCO-based round conductors.