Characterisation of YSZ Layers Deposited on Y2O3 Buffered Textured Tapes for Coated Conductors

Yttria-stabilized zirconia (YSZ) films were deposited on Y2O3/Ni-5at.%W substrates serving as the barrier layers for coated conductors by reel-to-reel direct-current (D.C.) magnetron reactive sputtering. The deposition parameters, such as the substrate temperature and tape moving speed, were systematically investigated. X-ray diffraction analysis confirmed that optimized YSZ/Y2O3buffer layers showed excellent in-plane and out-of-plane textures. Atomic force microscope revealed a smooth, dense and crack-free surface. The subsequent CeO2cap layer and 1μm-thick YBa2Cu3O7-δfilm sequentially prepared, showing the critical current densityJcunder 77K, self-field of 1.4MA/cm2.

Coated Conductor: Some Critical Aspects from Substrate to Device

This work reports some new studies related to critical aspects in the development of coated conductors (CC). New bi-axially textured tapes based on commercial copper alloys were fabricated and tested as substrates for LZO buffer layer deposited by chemical solution deposition (CSD). Such a layer form cube texture on NiW5 and Cu55Ni45 with an identical or even better texture than that of the substrate. It was shown that a S c(2x2) sub-layer formed at the metallic surface as a positive effect on the nucleation. The crystallisation of LZO on Cu55Ni45 still has to be improved, being inhibited by trapped C in the film. Recent progresses using our continuous MOCVD system are shown. A CC fabricated by an all MOCVD process has been obtained on SS/YSZIBAD substrate with high transport critical current (170 A/cm-width, at 77 K). It is also shown that LZOMOD can efficiently protect Ni5W RABITS from oxidation during deposition of CeO2 layer by MOCVD under 30-40% O2 partial pressure. This opens the possibility to fabricate a CC on RABITS by MOCVD. This shows that a mixed MOD/MOCVD approach could be efficient. Finally a 2m long CC SS/YSZIBAD has been tested for fault current limiter applications. Best limitation was observed at 86 K where an equivalent energy of 340 J has been dissipated in the CC during 12 ms without apparent damage of the CC. In a subsequent operation, the CC was however destroyed. The causes are discussed in the perspective to design better architectures for this application.

ELECTRODEPOSITION OF BIAXIALLY ALIGNED TL-BASED SUPERCONDUCTORS ON AG TAPES

An alternative preparation method of Tl based superconducting tapes is discussed. We developed Ag textured tapes as substrates: this material can be used without any buffer layer owing to its weak chemical interaction with the HTSC. Electrodeposition proved to be a fast, cheap and suitable technique to deposit a precursor that can be subsequently transformed in the superconducting phase by an opportune thermal treatment. The solution is formed with nitrates of all the metals dissolved in DMSO. The as-electrodeposited precursor is a highly reactive mixture at atomic scale of all the metals; a rapid (~30 min) thermal treatment is performed in a high isostatic pressure furnace (1 bar O2/50 bar He) in order to prevent Tl evaporation. Epitaxial growth of Tl-based superconductor was achieved by this technique on <110> textured Ag, both on single crystals and on oriented tapes. Superconducting transitions are observed at ~60 K and ~118 K for Tl(1212) and Tl(1223), respectively.