High Performance Coated Conductors Fabricated by UTOC-MOD Process

Abstract

A new metal organic deposition (MOD) process using precursor solution containing metal trifluoroacetates was developed to improve in-field performance. In this process, the pinning centers of BaMO 3 (M: metal elements such as Zr and Hf) materials could be made to be finer by reducing the once coating thickness in the coating and calcination step. This is referred to as the ultrathin once coating (UTOC)-MOD process. This process improves the in-field performance. The UTOC-MOD process also has the advantage of uniformity of 2-dimensional J c-distribution, which was determined using a scanning hall-probe microscopy analysis. Improvement of the J c uniformity was also confirmed based on scribed tapes. A smaller dispersion of the filament-critical current values in the UTOC-MOD tape was determined based on a comparison with the results for obtained by a conventional process. With respect to the mechanical strength, it was established that the dispersion of the delamination strength, which was evaluated using stud-pull equipment, was suppressed. Microstructural analysis revealed that, the UTOC films were pore-free, although large pores are present in the films when conventional MOD is utilized. This difference in the microstructure can be attributed to the aforementioned improvement in the uniformity of the UTOC-MOD films. Index Terms-High-temperature superconductors, critical current density, flux pinning, yttrium barium copper oxide, superconducting tapes. I. INTRODUCTION R E-Ba-Cu-O system superconducting coated conductors (CCs) can potentially be utilized in a wide variety of applications because of their high performance in magnetic fields. Among these applications, many are based on magnetic behavior such as magnetic resonance imaging, motors, generators, and accelerators. Through the development of CCs, in-field performance including critical current density (J c (B)

Progress in superconducting REBa2Cu3O7 (RE = rare earth) coated conductors derived from fluorinated solutions

“…The main consequence of this reduced ratio is that the YBCO growth temperature is decreased and the superconducting properties improved due to the modified microstructure [31,53,57,[74][75][76][77]. Microstructural studies have shown that these non-stoichiometric compounds display a reduced porosity and a lower concentration of a/b nucleated crystals while the expected secondary phases (mainly Y 2 Cu 2 O 5 and CuO) do not perturb in a relevant way the epitaxial microstructure and so this modified metal stoichiometry has been widely used by many authors to grow CCs displaying very good superconducting performance [57,74,76,[78][79][80][81]. It is also worth to mention that the validity of the TFA approach has been widely proved for most of the Rare Earth compounds in REBCO films where high superconducting performances have been demonstrated [40,73,82].…”

“…It was shown that above a concentration of 10%-12% mol in the final YBCO layer there was a tendency towards NP aggregation and the size control of the NPs was compromised [90,91]. An alternative deposition approach was devised which hindered the NP diffusion and coarsening by taking advantage of the CuO interlayer formed at the intersurfaces of multideposited pyrolyzed films, called UTOC [40,[79][80][81]. This novel process selects ultrathin (∼30 nm) YBCO layers and a solution multideposition approach to reach competitive total film thickness and critical currents, for instance, 35 repetitions of the spin-coating/pyrolysis cycle were required to get a final film thickness of ∼0.6-0.7 µm [40,92].…”

“…In all cases the REBCO growth process of the thick films needed to be reformulated to reach high superconducting performances. Slot die coating has been demonstrated to be a suitable industrial approach to prepare CSD CCs in long lengths when a multideposition approach is used because it can be adapted to a multilane automatized manufacturing system [30,31,63,79,[148][149][150].…”

Current–voltage curve of the high temperature superconductor with local reduction of critical current

“…Such modification is motivated by the reports of conductor damage caused by locally reduced critical current leading to hot spot creation [30][31][32][33][34][35]. It is well documented that the electric current in thin high-T c layer should avoid local imperfections [36][37][38][39][40][41][42][43][44]. Because of a highly nonlinear rise of voltage with current, the regions with lowest critical current would form hot spots, coexisting with the neighboring superconducting regions [45].…”