Synthesis of thick YBCO films up to 3.0 μm on metallic substrates by a fluorine-free metal organic decomposition method

Abstract

We improved the critical current properties of fluorine-free metal organic decomposition processed YBCO thin films prepared on buffered metallic substrates by increasing the thickness of the films. YBCO films prepared using a conventional one-time growth exhibit a maximum Ic (77 K, ∼0 T) value of ∼100 A per 1 cm width for a film with a thickness of 0.8 μm, and Ic decreases with further increases in the film thickness due to the generation of impurity particles and micro-cracks. In this study, a multiple growth process was adopted for the preparation of thick films to avoid these problems. The Ic of films prepared using this method monotonically increased with the film thickness. YBCO films with a thickness of ∼3.0 μm recorded a quite high Ic (77 K, ∼0 T) value for ∼210 A cm−1 width. Additionally, the in-field Jcs at 20 K and 40 K were found to increase almost proportionally to the film thickness.

Enhancement of self-field critical current density by several-tens-MeV ion irradiation in YBa2Cu3O7 films prepared by fluorine-free metal-organic deposition

“…Our results directly indicate that discontinuous 1D pins that have the properties described above are effective for enhancing J c sf at 77 K of YBCO, not only in the 100 kA cm −2 -order of bulk samples as previously recognized, 18) but also in the MA cm −2 -order of film samples. Our results also indicate that the relatively low J c sf performance in thick FF-MOD YBCO films (J c sf < 3 MA cm −2 at 77 K and t ∼ 1 μm 19,20) ) with respect to other deposition methods (J c sf > 3 MA cm −2 21) ) is attributed to lack of pins rather than to a degraded superconducting matrix.…”

“…The as-grown FF-MOD film showed a strong negative J c sf (t) relation, in contrast to the nearly constant J c sf (t) in the as-grown co-evaporation film, but agrees with the "deposition thickness" dependence. 19) The J c sf (t) curve of the FF-MOD film treated with 66 MeV/1 × 10 11 cm −2 Au irradiation significantly differs from that of the as-grown data around t = 800 nm, thus indicating a sizable J c sf enhancement due to the irradiation. But this difference gradually shrinks on decreasing t, and eventually vanishes at t ∼ 300 nm.…”

“…FF-MOD has recently attracted renewed attention for its enhanced achievable t (>1 μm). 19) But it has also been recognized that I c sf of FF-MOD films does not increase linearly with t (inset in Figs. 3, and 3 of Ref.…”

“…19), unlike other deposition methods such as PLD and TFA-MOD. 1,21) As a result, FF-MOD can yield very low I c sf of about 200 A cm −1 at 77 K at best, 19,20) implying a critical disadvantage in application compared with other deposition methods that yield I c sf > 500 A cm −1 at similar temperatures. 1,21) The reason for the strong suppression of J c sf in thick FF-MOD films has not previously been clarified.…”

Superconducting joints for the 1.3 GHz persistent NMR magnet under JST-Mirai Program

“…Among the various methods to prepare REBCO bi-axially oriented thin films, the metal organic decomposition method using fluorine-free starting solution (FF-MOD) is considered as the most suitable way to connect REBCO tapes, because bi-axially oriented REBCO layers with a flat and clean surface grow on the substrate having a bi-axially oriented surface layer in a short time [13]. In addition, the multiple sintering method is effective to increase the critical current of the REBCO tape by this method [14], meaning that a bi-axially oriented REBCO layer can be grown on the REBCO layer of commercial tapes. Elimination of the residual carbon in the calcined REBCO film is essential for crystal growth with few impurity particles on the film surface and, therefore, pre-heating at ∼650 • C is carried out before epitaxial growth of the REBCO layer at ∼800 • C in a moderately reducing atmosphere of P O2 = ∼10 Pa.…”